# Some people build Models, others build CNC PLASMA machines



## rodw (Aug 20, 2016)

This thread might take a fair while to develop. Its been 12 months in the making already. My Arduino Rotary table controller project got me interested in CNC but I did not want to do the obvious and convert my mill to CNC. I eventually got interested in CNC plasma cutting and I started about 12 months ago by cramming the electronics into an old Plasma machine case complete with a Torch height control. There are 3 layers of electronics in the case.







I got very disollusioned becasue my cheap plasma cutter died and the parallel port Break Out Board refused to talk to the PC.

So it sat on my desk for the next 10 months or so until one day I remembered how much time and effort went into it so I decided to kick start the project again. So in June, I purchased a 50 amp Everlast Plasma cutter with CNC interface and a CNC torch for it.

After hundreds of hours designing a machine, it is finally coming together. After machining 20 or so parts, finally, the Z axis is complete and I am sure it will work nicely.

Originally, I was going to make a ghetto build machine but since I got the idea, I've purchased an interest in a business that could use a plasma cutter so I am sparing no expense to do the job right. As I am surrounded by fabricators, the table will also be of commercial quality.

These are just quick pics taken with my phone, I will post up some better ones one day if I find the time to pohotograph it properly.











It has a 150mm ball screw which gives total travel of about 100mm. You can see that there are 2 linear rails. One is for the Z axis itself, and the other is a short floating section that senses the material.

Plasma is a bit different to other CNC machines as there are no cutting forces. Here is what happens at the start of a cut.
1. The torch rises until it trips the home sensor which you can see below the black bearing mount on the stepper side.
2. The torch hits the material and moves up along the floating rail. This trips the upper proximity sensor.
3. The torch height is adjusted for the switch hysterisis.
4. The torch raises to cutting height (around 250% above cutting height)
5. The controller fires the torch.
6. Once the Arc is established, the Plasma cutter sends an ARC OK signal back to the CNC controller
7. The torch is lowerd to the cutting height and off it goes.
8. The CNC controller monitors the arc voltage sent back though a voltage divider from the Plasma cutter as the voltage is a function of torch height.
9. The torch height is maintained constant based on this voltage as parts can tip up or warp while being cut.

The red micro switch is a limit switch so the ballscrew does not fall apart. In theory, it should never be tripped as the material sensor should always be triggered before it.

The other thing that could happen is the torch could hit something that could damage the machine. To protect against this, I've added a breakaway magnetic Torch mount.






This has  5 x 12.5mm dia magnets that are 3.5mm thick. These have been pressed into holes cut with a 12.5mm endmill so they are just proud of the mounting surface. They are secured by 3mm countersunk screws. The locating pins have been machined using my boring head ball turner documented elsewhere on this forum which are a press fit (helped with some retaining compound. This is the second iteration of the magnetic breakaway mount. Initially I wanted to use a pair of North and South oriented magnets so that one magnet was sitting below the surface and the other located into the recess. I found the magnets were not dimensionally accurate and also turned out to be a press fit. Breaking an M4 tap on th elast hole was the final straw but I decided the part needed a total redesign and went with a steel plate located by the pins.

If the torch ever falls off, it makes sens to stop the machine immediately so I've drilled and tapped the back side for another proximity sensor which will return an e-stop if it ever triggers.






The reason why the torch mount is a lot lower than the carriage is that I hope to be able to build a cover for the axis to keep out metal dust.

This machine will be controlled by LinuxCNC and I have purchased an Ethernet Mesanet 7i67E interface card and the matching MESA THCUD torch height controller daughter board. Unfortunately, the Mesa board is significantly larger than the Breakout board in the yellow case, so everything needs to be stripped and remounted into a 500mm x 500mm enclosure I've purchased.

Today, I managed to drill and tap 44 x 4 mm holes into a piece of Aluminium RHS on my little SX3 mill. This proved quite a mission as the X axis handle sits proud of the mounting table so the RHS had to hang off the table to get about 2mm clearance from the handle.






Its a bit hard to see but there is a length of 75mm x 50mm steel mounted to the table to act as a fence so I could slide the material along. I used a short piece of scrap linear guide when I had to reposition the material (table travel limited me to 7 holes at a time and there are 22 on each rail.). I've screwed this scrap down with 2 screws and located the undrilled hole with a close fitting punch. This worked pretty well but on the first side, I started at one end and was out a bit by the time I got to the other. On the second side, I started in the middle to halve any error.











The problem with this setup is that the holes have been referenced on 2 different sides so I don't really know exactly how far apart the rails are. That won't be hard to sort out.

I clamped one rail to the back fence when mounting it. The steel fence is dimensionally accurate, but I've forgotten the accuracy spec. The second rail is still loose and will be tightened up once I get a carriage mounted up.

I'll try and post up a few more photos tomorrow as I hope to get the Y axis close to finished. The plan is to have 2 linear rails on the front face of the RHS and a gear rack for the rack and pinion drive mounted underneath to shield it from dust as much as it can be. This is going to be a bit of a pain as its designed to be mounted from the rear into M6 holes in the rear of the rack. I'm going to have to drill access holes on the top surface to fix the rack. I'm glad thes holes are much further apart than the 60mm on the linear rails!


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## Cogsy (Aug 20, 2016)

Good luck with your build - I know how tricky they can turn out to be. Here's a pic of one I built a few years ago.


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## rodw (Aug 21, 2016)

Cogsy said:


> Good luck with your build - I know how tricky they can turn out to be. Here's a pic of one I built a few years ago.



Cogsy, thanks for the encouragement. Hopefully all the bad luck got left behind last year in the yellow box. My table will be similar to yours. 

Did you have to add gearing to your steppers for the rack and pinion or did you get away with direct drive? My pinion will give 30mm per revolution and I was hoping to get away with a direct drive.

I thought after I bought my linear rails that it probably only needed one based on their torque holding specs.

Anyway, I did not have as much time as I had hoped today but I wanted to get the rails in position and confirm they were parallel.



Here's what I ended up with.






The part connecting the linear carriages is just some scrap as I did not want to disturb my mill setup until I have mounted the gear rack.

I used transfer screws and a tap with a hammer to locate the holes. There is only 6 in the set but more than enough for this exercise.











Once this plate was nice and secure, I went along and tightened up the second rail  one bolt hole at a time with the carriage positioned right beside it to set the width.

It turned out really well. So happy, absolutely no binding along the full length of travel (1240mm Y axis width).

So now all I have to do is to mount the gear rack, make the mounting plate to replace the temporary one, finalise the stepper motor pinion drive setup and mount the Z axis to have the Z and Y Axis done and dusted over the next week or 2.


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## ShopShoe (Aug 22, 2016)

Rod,

That's an impressive project. For all-around work it looks like it's going to be a very useful tool. I'm looking forward to posts with some of the things you will make with it when it's done.

Thanks for posting.

--ShopShoe


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## Cogsy (Aug 23, 2016)

rodw said:


> Did you have to add gearing to your steppers for the rack and pinion or did you get away with direct drive? My pinion will give 30mm per revolution and I was hoping to get away with a direct drive.


 
Both X & Y were direct drive via timing belts, no rack and pinion at all (although I'd have preferred it). Z was just direct drive ball screw. You probably know it already but you want pretty much the fastest travel you can get out of it in X & Y so try for direct drive if you can. 

A nice blast shield around the torch nozzle really helps keep the grit out of the drive systems and allows you to watch the cut without going blind as well. 

One of these days, when I have the time, money and somewhere to put it, I'll make a half-sheet one for home.


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## rodw (Aug 23, 2016)

ShopShoe said:


> Rod,
> 
> That's an impressive project. For all-around work it looks like it's going to be a very useful tool. I'm looking forward to posts with some of the things you will make with it when it's done.
> 
> ...




Thanks for the encouragement. I'm trying hard to make it commercial quality all the way.



Cogsy said:


> Both X & Y were direct drive via timing belts, no rack and pinion at all (although I'd have preferred it). Z was just direct drive ball screw. You probably know it already but you want pretty much the fastest travel you can get out of it in X & Y so try for direct drive if you can.
> 
> A nice blast shield around the torch nozzle really helps keep the grit out of the drive systems and allows you to watch the cut without going blind as well.
> 
> One of these days, when I have the time, money and somewhere to put it, I'll make a half-sheet one for home.



Cogsy, Thanks, you see so many with reduction gearing but the maths say to do it pretty direct. I did see it said the ideal speed was around 1" per rev so 30mm per rev is pretty close to that.

Z axis is running a 5mm pitch ball screw.

Been busy the last couple of days so no progress, I need to think out the Y axis wiring and stuff before I build too much more. Bought some more material today.


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## mjonkman (Aug 28, 2016)

I'll be following this thread. I want to build a combination cnc plasma cutter and cnc router next spring. I don't have room for one that could take a full sheet of metal so I'm planning on building mine with a cutting area of  4'x4' which is probably still too big for my small shop but I'd hate to go any smaller. Definitely be trying to understand your design to see if I can pickup any tips for when I start designing mine.


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## Wizard69 (Aug 28, 2016)

mjonkman said:


> I'll be following this thread. I want to build a combination cnc plasma cutter and cnc router next spring. I don't have room for one that could take a full sheet of metal so I'm planning on building mine with a cutting area of  4'x4' which is probably still too big for my small shop but I'd hate to go any smaller. Definitely be trying to understand your design to see if I can pickup any tips for when I start designing mine.




Not to throw water on the fire but trying to build a combo machine leaves you with a lot of trade offs that are less than ideal.  Plasma machines really benefit from light weight designs that allow for high accelerations and high speeds at low costs.  For a router rigidity is more important as you have to counter real reaction forces from the cutter plus surface finish quality increases with rigidity.  

Im not saying it can't be done, just that you need to realize that if you design for one use you will loose for the other use.  Of course your expectations are a factor here.   

By the way I understand the frustration of a small shop!   I'm stuck in a basement at the moment and need to work miracles just to make use of a bunch of rather compact metal and wood working tools.  If you are already tight on space I'd suggest laying out the machine in a cad view of your work shop.   Either that or build a CAD (cardboard aid design) template of the foot print and see how it will fit your shop.   Actually a full so all card board template will highlight usability issues right away as you can walk around the "machine" to get a feel as to how convenient a real unit will be.   

I only bring this up because siting a machine creates huge problems in small shops.    For example I bought a small jointer as I don't expect to be doing massive wood working projects.    Even so I ran into usability issues because even with a small jointer you need three side access.   

By the way there is the option of placing a plasma unit outside.   It would have the advantage of fire safety and you can build any size you want.  Build the majority of the machines frame from aluminum and rust isn't an issue.


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## rodw (Aug 29, 2016)

mjonkman said:


> I'll be following this thread. I want to build a combination cnc plasma cutter and cnc router next spring. I don't have room for one that could take a full sheet of metal so I'm planning on building mine with a cutting area of  4'x4' which is probably still too big for my small shop but I'd hate to go any smaller. Definitely be trying to understand your design to see if I can pickup any tips for when I start designing mine.



Further to Wizards comments, the difference between the two is that plasma is built for speed (up to 10 metres per minute) and the router is built for torque so it travels much slower. By comparison, a mate's CNC mill travels at 1.5 metres per minute while I'm aiming for 10 metres. He's still scratching his head about why I'm using rack and pinions when he'd use ballscrews. The difference is 30mm per rev on my rack v's 5mm per rev for a ballscrew.

Whilst a multi-purpose machine can be done, the difference  is likely to become a compromise due to totally different design considerations. (light and fast v's slow and heavy). 

Regarding full size sheets, I am hoping to have a simple pull out trestle on wheels at one end that will support a full sized sheet when required.

I did not get much done over last weekend other than make a shaft adapter to mount a pinion to a stepper. I needed to do that to work out some key dimensions.

After conferring with my CNC mate and mentor, I tried 2 different Y axis drive designs (top mount and bottom mounted racks) and was still not happy. I think I've worked out how to make a front mounted rack that sits centrally between the linear rails as the best option. There is so much to consider to ensure that limit switches and cables are mounted and routed nicely. If I'm lucky, I'll have it drawn up during the week ready for the weekend.


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## mjonkman (Aug 29, 2016)

If I do build it, it will be built primarily as a CNC router and secondarily to work with a plasma torch. Hadn't really considered the need for speed on the plasma side. Obviously a lot more research to do, just toying with ideas in my mind at the moment.

Mark


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## rodw (Aug 29, 2016)

mjonkman said:


> If I do build it, it will be built primarily as a CNC router and secondarily to work with a plasma torch. Hadn't really considered the need for speed on the plasma side. Obviously a lot more research to do, just toying with ideas in my mind at the moment.
> 
> Mark



Depends what you need to cut. Thin stuff needs the speed. Find the Hypertherm 45 manual and look at reccommended speed tables in it before you get too excited. If you are only cutting say 3mm plate as a minimum, you may be ok.

There is a world leader in plasma and routers here in Brisbane and their commercial tables are built on a router gantry and you can add a drilling head with tool changer. But the one they showed me cost $135k and the drill was another $15k....! They started with routers and migrated to plasma and are found in shipyards around the world. The router table design was rebirthed as a plasma design.


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## rodw (Sep 4, 2016)

Sorry this thread has been inactive for a while, but with the Z axis complete, I've really been struggling to work out how to build the Y axis. The main consideration was where to mount the gear rack. I built near complete designs with the rack mounted on both the top and bottom of the Y axis RHS beam but found that when you took into consideration all the wiring and the like, they were not going to work. There is sooo much to consider.

So then, I came up with a design that mounted the rack on the front face between the linear rails.

Through this process, my research indicated that to control backlash, you needed to run a spring loaded pinion drive like this one available from CNC Router Parts.




See: http://www.cncrouterparts.com/images/CRP301-00-01_1920.jpg

But the problem is that this design also introduces a lot of wear in the rack so I really wondered if this was the right way to go.

So eventually I asked some questions on the LINUXCNC forum and as I suspected, people were getting away with direct mount pinion drive even on commercial products. You can follow the discussion on this thread.

https://forum.linuxcnc.org/forum/30...-you-really-need-a-spring-loaded-pinion-drive

On this thread, I proposed this design





And people said I should support the Pinion drive to protect the bearings in the stepper motor. I remembered, I had a surplus bearing block so I modified it






Andy said, just build it and so I made a start,






but stuffed up reading my own drawings so will have to remake the part. So you will have to wait for another weekend.


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## rodw (Sep 18, 2016)

I have not had much time the last few weeks, but I finally got in some quality shed time over the weekend and got this done





This is the drive for the Y axis on the gantry. From the earlier renders, you should be able to work out where this goes.

I am very happy with how this turned out. The shaft, stepper and bearing alignment is absolutely perfect. The pinion turns nice and freely.  I'm still not sure if have clearance between the bearing block and the guiderails but the CAD model said I just made it. If I don't I'll mill some of the bearing block away.

It will be a couple of weeks before I can fit in another shed session but there are only a few more parts to make (and one to remake :fan


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## rodw (Oct 9, 2016)

Its been weeks since I've had time to tackle anything further on this. 

I made a bit of a mistake with my design. My calculation was out by a factor of pi (3.1417) so when I thought I was turning 30mm per revolution, I was actually turning 94.25 mm! This was going to be a major issue in terms of machine accuracy so I had to redesign the Y axis drive to put in a 3:1 reduction drive system to get it back within the ballpark at 31mm per rev.






You can see I've used a WBK ball screw bearing assembly. You can also se the slotted belt tensioning adjustment.





This reduction drive assembly is a bolt in replacement for the original stepper motor and bolts on where the stepper used to.

I still need to turn up the shaft. Its going to be tricky and I'm not looking forward to it as it will involve cutting an M12 x 1 thread in one pass.

I could not mount the stepper square on as the belt would foul the front legs.  I decided to try mounitng the stepper clocked 45 degrees and hope the leg did not foul the large pulley. 

I wish I had found the belt feature in my CAD software beforehand. I knew the stepper posts were going to be close to the timing belt cog but it actually fouled the cog.






Anyway, in the revised design, I've clocked the stepper leg mounting plate around a bit further and have clearance now in a revised design that rotates the legs about 20 degrees.






I only need to re-make one simple part that the legs attach to. It has 8 holes drilled and tapped so it is easy enough to make.

One of these days, I'll actually have this  gantry complete!


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## rodw (Oct 23, 2016)

I finally got the Y axis pinion drive built, the rack and pinion installed and the  Z axis installed. Everything moves quite smoothly by hand. I still need to fit up the Y axis limit switches but know how I'm going to do that now. I will get onto the electronics  in the next couple of weeks.











Clearance for the belt 






Pinion Drive Shaft detail.






This also shows the full length 20mm x 6mm packer under the rack so the bearing block cleared the guide rail. You could probably avoid the need for this if you made the shaft longer. In practice, making the packer strip and drilling all the holes in it before hand made it easy to drill the holes into the gantry. There was exactly 50mm between the two guide rails. My end stops I had machined to be 15mm high which was the exactly the required distance each side of the 20mm wide packer. I used them to set the position of the packer.  Initially, I drilled and tapped holes for each end of the packer and bolted it down securely, then I used my improvised 15mm spacer to align the packer perfectly while centre punching with a transfer punch to get the punch centred on the hole. With all the holes drilled, I the drilled the threaded holes out and bolted it all together.

Because this  gear rack has threaded mounting bolts on the reverse side and I was mounting it to a 80mm x 40mm RHS, I had to drill clearance holes right through so I could secure the rack using socket head cap screws using an allen key.  A blob of grease helped hold the bolt on the end of an allen key as I inserted it.

To tidy it all up, I added some rubber grommets on the reverse side.






Its going to be a while before this will be moving. There is still a fair bit to do to the gantry to add limit switches and all of the wiring. I've got most of the stuff I need here.

I'm very pleased to get the gear rack mounted up. The supplier said it was 150mm hole pitch but it actually worked out to be exactly 5.75" (which I promptly converted to metric to build the darn thing! I will say drilling 9 holes 146.05mm apart was a bit crazy.


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## rodw (Jan 1, 2017)

Well, its been ages since I posted any updates here. I've had a few trials and tribulations along the way.

I found that I needed to use the preemptive kernel for Linux to get the Mesa Ethernet card working properly and this proved a major tasks. I installed the kernel on my 32 bit PC and the latency went out the window so I had to buy a new PC





Then a week of frustration followed and I finally installed Linux Mint 17.3, upgraded to the later 4.13 kernel, applied the preemptive patch to the kernel source code and compiled the LInux Kernel from scratch. Then I had to resolve all of the dependencies and compile LinuxCNC for the different flavour of Linux. As you can see, this is a massive PC. With the single Network interface reserved to talk to the Mesa card, the internal Wifi card introduced huge latency so I am running a USB wifi card to talk to the world from my garage.

While this was happening, I put a fair bit of work into the enclosure















I added green, amber and red indicator lights. While the machine is running it is green, if it is idle, it is amber and if in estop, its red.

A small blue LED  on the far left indicates when the Plasma ArcOk signal comes on.

The red and green switches act as a run/stop and pause/resume switches.

I would like to make the green light flash when its in a pause state but I decided I had too much to do to get it functional.

I must take some photos of the electronics now its almost all wired in.

I got the gantry complete and running at about 21 metres per minute (well over 800 inches per minute for those that are metrically challenged)






The movement is spot on and there is no backlash. I let it loose for 20 metres up and down the gantry and it finished exactly where it started off on.

I decided I better tidy these bolts up 




and ordered 20 M5 dome nuts from my bolt shop. 




THe bill turned up and to my amazement, what you are looking at is AUD $158.60 worth of dome nuts! Well at least they were solid brass! After a terse email, the price dropped back to a more reasonable $7.60 or so. I was glad about that becasue I had ordered the wrong size and already had the correct M4 dome nuts to hand.






There is an insane number of sensors on the gantry (7 actually) so I decided to cheat and buy a 5 metre DB9 cable and build a breakout board. Using 2 wires for 24 volt power, I had just the right number of wires for the sensors I needed.






I made a bit of a mistake as I bought NPN proximity sensors only to find out that I should have used PNP sensors with the Mesa hardware so I had to add some pull up resistors  which are also soldered onto my breakout board as you can see above. I also added a 24 volt LED indicator that pokes up throuh the top of the gantry to help with trouble shooting.

I have 3 proximity sensors in a row






The outer ones are limit switches and the inner one is the home switch.

These see the limit/home switches






The home sensor is  a lot lower than the limit switch so it sees the edge of the mounting bracket. Once LCNC sees this, it backs off, approaches slowly to find the edge precisely and then there is a HOME_OFFSET setting that then lets me park the sensor  wherever I want.  I use it to park it as close to the end of physical travel as I can without th elimits being triggered.

The Torch breakaway sensor has been OR'ed with the external e-stop switch.






So if the torch falls off, the machine stops immediately.

Last week, the 25mm Hiwin linear rails and carriages arrived for the X axis and a day later the these NEMA 34 timing belt gear boxes arrived






They are about 4:1 ratio and they drive a 1.5 module helical pinion that engage with a 1400mm long rack you can see in the left of the photo above.





With all of this arriving, I spent the last few days working flat out on finalising the table design






And this morning I prepared 15 files to hand off to my laser cutters and I've emailed that off for quotes today. I hope it is cheaper than the dome nuts!

I've also ordered the NEMA34 stepper motors to suit the gear boxes so I hope to have the table together by the end of January. Its been a piece of cake sorting out the table and X axis in comparison with the gantry and Z axis. I always knew they would be the hardest bits.


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## rodw (Jan 7, 2017)

Well, things are moving along pretty quickly now. I've ordered all of the laser cut parts to finish this off but with the Christmas break, I don't expect to see them until February which is a bit annoying. Hopefully they will surprise me.  The NEMA 34 stepper drives for the X axis have been shipped and should be here Monday. There is about 80 holes to tap. I was going to get the Laser guys to do this but they were pretty expensive so I bought a magnetic hand tapping guide on Friday.






The money I saved paid for the tapping guide and a motorguard air filter that are meant to be the ducks nuts for plasma cutters which don't like dirt or water in their air supply.

I also managed to get one of 2 hand encoder wheels running. The other will just be a copy of what I've done. This is where the Mesa card starts to come into its own as it has 2 MPG (manual pulse generator) encoder inputs on the board.

I've just mounted the MPG wheel on a piece of scrap for now. This is a 100 pulse per revolution encoder. I will use one on the X axis and 1 on the Y axis.






The other part of the encoder is to have a switch to select the scale it uses. To do this you can use a 4 input binary switch and the Linuxcnc mux4 component. This proved quite tricky but eventually I worked it out. Using the mux4 component allows you to support 4 options with just two inputs by using binary logic like this.

```
0: 0 0
1: 0 1
2: 1 0
3: 1 1
```

So on the switch, you need to make sure wherever there is a 1, you have a voltage signal so I wired them to 24 volts.





So with this done, I told LinuxCNC to use the following scale settings using the mux4 parameters as follows:

```
0: Off/Disabled
1: 1 mm per pulse
2: 0.1 mm per pulse
3: 0.01 mm per pulse
```

And it worked!

So when I do this on the Y axis, I am going to add another switch so I can select between jogging the Y and Z axis. I Wan't going to bother with jogging the Z, but it will be so trivial to support, I might as well as I have not run out of  inputs yet!

The other thing I wanted to achieve was in addition to a Pause/Resume switch and a Run/Step switch was a series of warning red, green and amber lights. Ultimately, I want to have a set of stack lights on top of the machine that will act like a set of traffic lights so you can see the machine status from across the room as follows:
Red = E-stop error
Amber = Machine turned on at the LinuxCNC console
Green = solid on - running Gcode
Green = flashing on - in pause or single step mode.

This wasn't easy to achieve after first having the idea but the guys on the LCNC forum helped me sort it out

Anyway, I got it done this morning and here is a video of it and if you are into this sort of stuff, it is very cool.

https://youtu.be/5NYhmYO4mCs

So I'm getting close to completing the LinuxCNC config now. The next step is to configure the Torch height control module. I have not properly set up all of the axes yet, but I don't think that will be hard. Thats about the only 2 parts of the  config left to do.

So that brings this thread up to date.


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## ShopShoe (Jan 7, 2017)

Slight OT

Rod,

I don't think I've ever seen a magnetic tapping guide from any of my sources here in the U.S.A. Tell me more about it: It seems like a useful thing to have.

--ShopShoe


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## rodw (Jan 8, 2017)

ShopShoe said:


> Slight OT
> 
> Rod,
> 
> ...


ShopShoe, I had a chuckle when I'm posting about the 100's of hours of effort and all this cool technology and it is a hand tool that captures someone's interest 

Anyway, there is not much to tell as I have not used it yet! I got it from here
http://www.machineryhouse.com.au/T0119
It grabs the flats of the tap between two flat surfaces which slide from side to side.





And the tap is held central by the chuck tightened by a knurled knob.






The sliding holder is held captive by 2 bolts that engage a slot in each half of the vice like tap holder.






The tap is held very securely!

Anyway, here are a few more pics of progress.

I've been putting off mounting any connectors to the base of the enclosure as it will mean I won't be able to stand it up while I play with it.






So all the wires are coming out of the air vent (which is just a plumbing fitting with a grille cover)






There is a heap of diagnostic wires still attached that makes the internals quite messy. Shown here are a large blue LED warning light attached to the torch on relay that replaces the switch on a hand plasma torch. It is enabled by a Gcode M3 (spindle-on) command. That initial relay click was one of the most satisfying sounds I heard in the build! Above it is the jog wheel scale selector switch discussed earlier. Its a bit hard to see sitting on some stepper  motor control cable, but there is also a 100k potentiometer I've attached to test the voltage sensing circuit of the THCAD board that reads the torch voltaqe.

The electronics showing from the right, the Mesa 7i76e ethernet card, the matching THCAD accessory board and a switch to mimic the Arc OK signal sent from the plasma machine





Here is a closer look of the Mesa hardware. BLue ethernet cable enters at the top right. Its just a patch lead that leads to an industrial RJ45 connector on the side of the cabinet.






The first section includes the 5 volt section and there are 2 x 26 pin connectors which are unused. These are pin compatible with normal breakout boards and there is a heap of cool mesa cards you can attach to them as well. eg. Adding 2 non ethernet 7i76 boards would let me control a total of 15 steppers.

The next heavilly used conector are 4 of the step generators that go to the stepper controllers. There is a 5th unused step gen on the next connector.

The orange power connector is for 24 volt power. The small green connector is for spindle control and the THCAD frequency output is attached to the encoder input. (The THCAD is a voltage to frequency converter.)

The next 2 24 pin connectors are for field inputs and outputs for sensors and warning lights etc.There are 32 inputs and 16 outputs (maybe equivalent to 3 x parallel port breakout boards).

So the next small board is the torch height sensor. It takes torch voltage from the plasma torch at the top (in my case via 50:1 voltage divider in the plasma itself but it could take raw arc voltage). It draws 5v power at the bottom of the card and where the frequency output also resides. It can output at up to 1 Mhz (1,000,000 times a second) but I've enabled the 1/32 divider on the board as I'm only going to sample it at 1000 times a second.

There is a LCNC software module that takes this input and converts it to a voltage. The idea is that voltage is proportional to arc length (eg. torch height). So if LCNC can read the actual torch voltage, it can control the Z axis to maintain a constant voltage (or height). This lets it handle any warpage from the heat on thin stock or a thicker sheet or table that is not perfectly level. I  have about 85 mm of Z axis travel which should be heaps.

So when the gcode says M3 start your spindle, the final setup will lift the torch to pierce height, start the arc and wait for a pierce delay. The plasma machine establishes an arc and sends an arc Ok signal back to the CNC machine and the torch is lowered to cutting height and off it goes.


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## rodw (Jan 8, 2017)

The other thing that I have got working is my warning lights. I needed a little bit of help with these but I think they are very cool. 
Watch this video and see what you think.
[ame]https://www.youtube.com/watch?v=5NYhmYO4mCs[/ame]

I have ordered a stack light similar to this one which I want to mount on top of the machine so you can see it all going on at a distance when you are doing other stuff in the workshop.






So at this point, I've got all of the config set up with the exception of the Axes which need some work and the stuff to interface this to the LCNC GUI display.

Some of the setup has been quite hard, and I'm really happy I've finally got it almost all done.


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## joco-nz (Jan 8, 2017)

rodw said:


> I had a chuckle when I'm posting about the 100's of hours of effort and all this cool technology and it is a hand tool that captures someone's interest



Don't worry mate I'm captivated by all the techie stuff.   I am intrigued where you are going to fit this monster.  Clearly not in your shed.  

I am looking at what you are doing and using it to inform ideas for when I convert my BF20 to CNC.

Looking forward to videos of first automated cuts.  :thumbup:


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## rodw (Jan 8, 2017)

joco-nz said:


> Don't worry mate I'm captivated by all the techie stuff.   I am intrigued where you are going to fit this monster.  Clearly not in your shed.
> 
> I am looking at what you are doing and using it to inform ideas for when I convert my BF20 to CNC.
> 
> Looking forward to videos of first automated cuts.  :thumbup:



Yes, currently living in the garage beside my wife's car. I'm sure you can relate to that!  

Can you imagine how momentous the first automated cut will be if I got excited by hearing the torch on relay click!

D day won't be far away. Definitely before Easter.

Personally, I would recommend that you bypass Mach3 as its well and truly obsolete and go with LinuxCNC. Not knowing Linux  is not an impediment as they have a complete .ISO install image that installs Linux and LinuxCNC at the one time. 

There is also the stepconf program included which will build your config in a graphical environment and for a simple machine no hand editing of files will be required.

For a mill your size, I would not bother with the Mesa hardware. I'd grab something like this
http://www.omc-stepperonline.com/3-...r-m542t-driverr-kit-for-cnc-router-p-183.html
(My 3rd order from these guys is due to arrive on Monday. ) For you, just order from their global site and skip any GST. It just takes a few more days to arrive.

Grab any Parallel port breakout board. Unlike Mach, there are not any restrictions on parallel ports and one on the motherboard will work just fine. Look for a Celeron J1900 board or similar that runs on 12 volt power and treat it just like another component to wire into your enclosure. Any more grunt and you are wasting money. 2 mb is fine but hard to buy now so I'm using 4 Mb.

Breakout boards start at this one which I have here (Came free with my stepper drives)
http://www.ebay.com.au/itm/breakout...762289?hash=item3d204a8f31:g:xMgAAOSwqfNXjxQq

This is pretty crappy, a better board is a C10 which is not much more and has bidirectional ports so you can add additional inputs.

http://www.ebay.com.au/itm/C10-BI-D...015749?hash=item237af95445:g:w6AAAOSwJ7RYScNZ

Cheers mate, wear some paint off those machines you've bought and turn of that infernal plastic extruding contraption!


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## joco-nz (Jan 8, 2017)

rodw said:


> Yes, currently living in the garage beside my wife's car. I'm sure you can relate to that!



Hell yeah - that just described my whole shop.  :-D



> Personally, I would recommend that you bypass Mach3 as its well and truly obsolete and go with LinuxCNC. Not knowing Linux  is not an impediment as they have a complete .ISO install image that installs Linux and LinuxCNC at the one time.


Cool - I'm a Linux guy from back when configing and building your own kernel was the norm. Very comfortable with Linux and associated techs. 



> Cheers mate, wear some paint off those machines you've bought and turn of that infernal plastic extruding contraption!


I will. I have made a few supporting bits and pieces with the Lathe but in the middle of the mill table build at the moment. Lots of cutting steel and MIG sparks. Once mill is operational then have a nice little beginners engine to make. Plans all printed and ready to go.


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## ShopShoe (Jan 9, 2017)

Rod,

Thanks for the answer. I chuckled at your chuckle.

I like what you are doing with the high-tech stuff as well and I have a background which allows me to follow your descriptions of what's going on (just). I would love to start building something using Linux CNC myself, but the toy budget is in slow growth mode right now and life is in the way of much shop time. I am working on a stepper-driven indexer and rotary table and have made use of your posts on that topic.

Specifically, I like the panel layout and the way the lights work to keep the operator aware of the operating state of the system. The "Traffic Light" should work well in a multitasking shop (shed?).

Keep Building: You're keeping my interest.

--ShopShoe


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## joco-nz (Jan 9, 2017)

Rod - looking at the h/w you have suggested for a "light weight" setup versus the more industry path I believe you have taken, if you were to summarise, what do you see as the key advantages that the Mesa controller kit offers?

Cheers,
J.


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## rodw (Jan 10, 2017)

joco-nz said:


> Rod - looking at the h/w you have suggested for a "light weight" setup versus the more industry path I believe you have taken, if you were to summarise, what do you see as the key advantages that the Mesa controller kit offers?
> 
> Cheers,
> J.



Just a few.

1. 24 volt system not 5 v to combat noise often prevalent in industrial environments particularly on plasma system. No one uses 5v in the real world
2. Unlimited inputs and outputs by addding additional daughter cards for different purposes.
3. Built in jog wheel encoders
4. USD $69 torch height hardware supported by LCNC vs up to USD $1000 systems
5. Ability to use ethernet to separate PC from plasma noise (optional)
6.  Mach3 is a dead and obsolete environment.
7. Parallel port is dead and obsolete
8. Windows cannot offer a real time environment, LCNC can.

So never having used Mach3, even with a mate in my street who knows Mach3 backwards after building his own CNC lathe, I could not see any compelling reason to go with it. 

I chose LCNC over Mach in the first instance. I had a go at using a parallel port breakout board and failed so when I kick started the project again, I upgraded to Mesa. I now know that a faulty ribbon cable I made was the reason why the parallel port did not work initially.

The choice to go to ethernet substantially increased the complexity of the Linux install but thats another story.

For a small mill or lathe, a parallel port would work fine without spending $200 on a smooth stepper card and buying. M3 license.


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## rodw (Jan 10, 2017)

ShopShoe said:


> Rod,
> 
> Thanks for the answer. I chuckled at your chuckle.
> 
> ...



ShopShoe, 

Speaking of High Tech, this is where the idea for the lights came from. My old workplace, designed by me from the ground up. You can see a  stacklight mast on the machine  out of focus behind Mark's head at about 2:30 into the video.

https://youtu.be/PSbTux4CY3U

The machine in the background is one of  2 black and white devices we had running at 160 pages per minute. There were capable of running at 320 copies per minute and speed limited by a software licence key that cost about $80k to remove. We also had a colour device that ran at 70 pages per minute. The paper punch is a 100% mechanical device, no electronics anywhere! A testament to German engineering. All up about $1.0m of equipment.

We achieved 99.7% on time delivery in a 48 hour window, way beyond industry best practice. I think Xerox themselves worked on about 90%. Maybe thats why there is none of their equipment in the factory.


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## joco-nz (Jan 11, 2017)

Thanks for the pluses for the Mesa kit.   I do rather like the look of it but then I like robust solutions.  I'll focus on getting the mill working manually first then worry about this stuff.   I did find a local supplier who do some of the Mesa h/w.  The same lot I got a lot of my 3D Printer gear from.  A good bunch.

http://www.makershop.co.nz/CNC/Mesa


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## rodw (Jan 12, 2017)

joco-nz said:


> Thanks for the pluses for the Mesa kit.   I do rather like the look of it but then I like robust solutions.  I'll focus on getting the mill working manually first then worry about this stuff.   I did find a local supplier who do some of the Mesa h/w.  The same lot I got a lot of my 3D Printer gear from.  A good bunch.
> 
> http://www.makershop.co.nz/CNC/Mesa



Its great  you have a local source.  I got mine from John Thornton in the USA,  one of the key Linuxcnc forum members from here. http://mesaus.com

John has contributed some of the LCNC plasma torch height control code. Freight was reasonable and service was prompt. He has a lot of LCNC resources here http://gnipsel.com

I'm still not convinced on a small machine that you need to spend the money on Mesa as you can get by with a lot fewer inputs and outputs. Eg. Shared limit  switches or even no limit switches. It does make life so much easier to wire up though!


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## joco-nz (Jan 12, 2017)

rodw said:


> Its great  you have a local source.  I got mine from John Thornton in the USA,  one of the key Linuxcnc forum members from here. http://mesaus.com
> 
> John has contributed some of the LCNC plasma torch height control code. Freight was reasonable and service was prompt. He has a lot of LCNC resources here http://gnipsel.com


I found John's site in the last 24hrs, quite useful.  Even though I found a local supplier I can still land the gear from the USA cheaper than sourcing locally, so long as I keep under the GST radar.



> I'm still not convinced on a small machine that you need to spend the money on Mesa as you can get by with a lot fewer inputs and outputs. Eg. Shared limit  switches or even no limit switches. It does make life so much easier to wire up though!



Well there is what I could get away with then there is what I want to be able to do.   I quite like the idea of a 5th axis.   I definitely want limit switches up the wazzo. I now what a pain crashing a 3D printer can be due to only having one side of an axis limited.  I'm not taking that risk on something spinning at high RPM and costing a hell of a lot more dollars to fix if it really goes bad. Then through in half formed thoughts of a automated tool change, even if just to experiment with and the Mesa gear starts to look like the way to go.

I am intrigued with the ethernet over "parallel" cable choice. Is that really more relevant to the plasma cutters due to the level of electrical noise they throw out?  It looks a lot tidier from an architecture/design angle .i.e. no extra card in the PC meaning you should be able to go to a really small form factor mini/micro style ITX board with the associated small case.

Cheers,
J.


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## rodw (Jan 13, 2017)

With Mesa, you have a choice of either an ethernet solution (my 7i76e for steppers or its cousin the 7i77e for servos) Or a PCI/PCIe  solution. In that case, you plug a card PCI in your PC (probably a 5i25) and then you use a 7i76 or 7i77 daughter card which connects to the PCI card via a parallel port cable. The PCI interface has multiple DB25 connectors for the daughter cards.

The 7i76e is basically a 5i25 and 7i76 rolled into one card connected by ethernet. It supports 2 daughter cards so I could add another 2 x 7i76 cards which would let me control a total of 15 steppers. I think then I could add a RS485 interface board that would allow me to add another 4 I/O cards to increase the number of inputs and outputs if required. 

Aside from loading a different driver, PCI vs ethernet is totally transparent when you use it.

Tommy my LCNC plasma mentor on the forum says that putting your PC in there with the electronics with plasma is a surefire recipe to spend countless hours troubleshooting recurring random problems due to noise.

Most Plasma system use a high frequency start that generates a high voltage, high frequency spark to kick the plasma off. Mine has a blowback torch where the arc is started in the torch and once established, the tip blows back or retracts and thus does not generate the noise or HF. That style is much preferred for CNC systems as few torch height systems can handle the HF stuff. Mesa's THCAD card can...


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## rodw (Jan 13, 2017)

joco-nz said:


> i.e. no extra card in the PC meaning you should be able to go to a really small form factor mini/micro style ITX board with the associated small case.
> 
> Cheers,
> J.



Sorry. Did not address this. Yes, I'm using an ULTRA SMALL FORM FACTOR PC (USFF).

The only issue is that to get support for hardware, you need to run a later version of Unix than the LCNC distro. This for me meant compiling a newer kernal and then of course compiling LCNC from source.

The kernel upgrade can be reduced to a single script but LCNC compiling takes a bit of work due to the large number of dependencies that need to be installed.

The onboard wifi cards on these cards cause terrible latency so you need to use a USB wifi dongle to connect to the internet as the ethernet port is in use. IF I built another, I would find a USFF PC with a dual network interface.


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## joco-nz (Jan 13, 2017)

Thanks Rod.  When you get back to posting on build progress I, and perhaps others, would be just as interetsed in the software/electronics side of the build as the medhanical.  E.g. Wiring diags, models/versions of MBs/CPUs used, performanc characteristics/jitter/etc, good suppliers you have discovered.

A lot of what you a working through on the LinuxCNC side and associated electronics and controls I'm very interetsted in as I can see its application to any router style CNC table and much that can apply to a LinuxCNCing of mills or lathes.

I just cant let the wife get a hint of another possible project fasination right at the minute.  :hDe:

Hanging out for more  build posts.  :thumbup: :bow: th_wwp


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## rodw (Jan 14, 2017)

joco-nz said:


> I just cant let the wife get a hint of another possible project fasination right at the minute.  :hDe:
> 
> Hanging out for more  build posts.  :thumbup: :bow: th_wwp



Sorry, but I'm writing this on a Chromebook that crashed and lost my post. Very Annoying!

My wife would die if she knew what I've spent on this project!  

The detail is on the LCNC forum here
https://forum.linuxcnc.org/show-your-stuff/32029-rods-spaceship-scratch-built-plasma-cutter-build

Make sure you follow the links I post as many of them refer to links where I ask a specific question in another sub-forum  to make sure the right people see it and help me!

Anyway, today was 36.2 degrees according to my weather station just above my shed which means it would have been 46.2 degrees where I was working in a tiny corrugated iron shed.

I managed to fit the steppers to the 5:1 timing belt reduction drives before I expired in the tin sauna.  I emerged in a lather of sweat and was able to plug them in to my control panel which meant for the first time, I had all 4 steppers functioning.












I can't really do much more until I get the gantry ends installed  and the gantry up on the table as I need limit switches and homing switches so I can home it. Until I get that done, I can't run any gcode to tune it.

But at least all of the motors run in the right directions.

Off to ebay to order 6 more proximity switches. This time I will make sure I buy the right type (PNP)


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## rodw (Jan 26, 2017)

Well, I have not got any more of the machine built but I have been working on the software side of things which has been quite time consuming






All of the important buttons have been connected to the hardware now which was really hard work. This particular screen has a couple of buttons that I probably don't need (as they are designed to feed into the Gcode but I can set that in the Gcode that is generated from the nesting software. (Usually with plasma cutters, you are cutting multiple parts out of a sheet of steel that are nested and all cut at the one time.) Anyway, I'll probably clean up the interface as time goes on.

I've also installed a new  larger (10.5amp) power supply and rewired the NEMA34 steppers to run in parallel mode. This means they use a lot more power but will run at faster speeds so it looks like despite the lower gearing on the reduction gear boxes I bought, they will keep up with the Y axis at 18 metres per minute. Previously, they were flat doing 10 m/min. So I am happy with that!

I've also spent a fair bit of time researching how PID controls work. Now I've got into it, the torch height control in LCNC is  pretty basic but people say it works well. I've got some ideas on how to recode this but time will tell if its necessary or if it actually improves performance.

Hopefully I will have some laser cut parts next week and the fun will really begin!


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## rodw (Feb 20, 2017)

Its been a long time since I've updated this thread but a lot of progress has been made.

My plasma cut parts turned up





and the

parts all mounted up as they should have






very pleased about that 

And I got these huge 1.8 metre long 12mm thick rails that had abojut 50 holes I needed to drill and tap to moiunt the gear rack and the 25 mm linear rails. The small part will become the home and limit switches based on my already proven design.






The gantry ends are folded from 6mm aluminium plate






and whilst its hard to see, the pinion clearance was perfect.






Then on Saturday, I borrowed the work ute and grabbed all of the steel for the table






Once it was cut up, it did not look to menacing. The table frame is 100mm  x  4mm wall SHS.






and I managed to get one of the gantry ends mounted up and moving.






I had to drill and tap a couple of holes in the stepper mounting plates that are carefully aligned with features in the casting. This let me mount a piece of ally angle to mount the stepper wiring plug to.

I had a lot of problems calibrating the movement but manged to sort it out by trial and error against a  1 metre steel rule. On the previous rack I installed, I just worked out the maths and it worked out perfect. It is clear this rack and pinion was  non standard. Anyway, once I got it sorted, I sent the gantry up and down for 20 metres as seen in this video 

https://youtu.be/r8YuW3JrFNE

To find I was only out 0.02mm so 0.001 error per metre will do me!






So I think I will call that a wrap!

Today, I went and bought some 330 kg caster wheels and need to work out a couple more things before I start welding up the table. ITs probably going to weight about 400 kg when done so I had to have some casters other wise I would never be able to move it.

Also, on Friday evening a chap from the CNCzone forum tracked me down to see my progress. I think he got a bit of a shock how much work there is in a project like this. (I seem to remember I did too a year or so ago!)

I also found a bug in Linuxcnc and I spent a lot of time sorting that out in the code and on the weekend, the responsible developer released a fix based on the code I had written. I am pleased about that as I did not want to be maintaining code.

I have to say I've become quite a Linux nerd through this and have even checked out different development branches of the code that contained some cool new features that I am sure will work its way into an improved torch height control in time. 

Anyway, that brings you up to date.


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## rodw (Mar 9, 2017)

Well, I still have not tackled the table yet as life has been a bit busy. I also have been designing the last few parts for the table because this thing will be so heavy, I need to be able to get it on the 330 kg casters I've bought for it to move it round.






So I made a mount at the stepper end to hold a wiring socket. This required drilling and tapping the stepper mounting plate






I don't think I showed you guys the air regulator with the dessicant to dry the air.






After the air goes though these filters, it will also go through a Motorguard "toilet paper" filter which are often used on plasma cutters.






Which reminds me, I have not worked out how these will get mounted to the table 

Somewhere along the line, I found a super cheap welding fume extractor with a 5 stage filter but I don't think it will have enough airflow for the plasma table.






Last weekend, we went to see Adele here in Brisbane. 60,000 people the largest concert ever staged in Brisbane and the first hosted at the Gabba cricket ground since about 1978. It was really enjoyable.






Sunday, I wired in the last stepper driver and soldered up the cables to it.

I did a few CAD drawings in the evenings this week and I checked them last night and thankfully I found the error before I got it laser cut!

One of the things I had to check was the voltage divider on my Everlast plasma cutter. It has the option of raw volts or divided volts at either 16:1  or 50:1. The divider is selected by a jumper on the CNC board inside the plasma cutter. 

Plasma voltage maxes out at around 300 volts. My Mesa THCAD card has a 0-10V range so 16:1 was not going to work and 16:1 would not have great resolution as it would only go from 0-6 volts. I had this great idea to use a voltage divider so I could use the 16:1 divider. This would give me a full scale reading of about 9.375 volts so it will be so much better.

Peter from Mesa set me straight on the LCNC forum about how to do this. You don't need a traditional voltage divider circuit, you just need to add a resistor in series with the voltage signal. The value of the resistor is based on a formula in the manual. My Maths was way out and Peter kindly stopped me from buying a 0.1 ohm resistor when the correct value is 100,000 ohms!

It is rare to see a manufacturer to be so involved in a forum and the support Peter offers is simply amazing even building custom firmware for people using his hardware. 

Last night, I pulled my plasma cutter apart and checked out what voltage was selected






.

As it turns out, I did not need to becasue it appears to be set to the correct value based on the position of the jumper on the bottom right. I still have to put it together again. This morning, I had to drive past Jaycar electronics to pick up some material for my web site (10 metres of 60mm dia plastic that needs to be cut and faced into about 180 parts). So I stopped and lashed out all of 55 cents to buy a packet of 100k resistors.

So there you go guys, you are now right up to date and I am ready to build the plasma control cable now. I will have no trouble tucking the tiny resistor inside the cable backshell.


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## rodw (Apr 8, 2017)

Progress has been pretty slow. While I can kinda weld, Lee at work does it for a living so there is no comparison between what I can do and what he can do. Finally, the table is coming together.






The jig we are using is one we use to make truck bodies for utes and pickups. To get the linear rails square, we welded up one side as square as we could and then mounted the linear rails. Then I fitted some angle iron brackets to the linear carriages and welded up a crossmember that spanned the two linear rails. YOu can see it in the pics. Once we got the second side clamped in position, I could push the rails along with one finger. So at that point, we tack welded the second side in position.

Unfortunately Lee has been pretty busy so has not had the time to finish this off.

I've also been plagued with some problems with spurious  limit switch errors on the gantry sensors (there are 7). I think today I found the problem.






Circuit boards are meant to be flat right? I have to rethink how to do this...


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## joco-nz (Apr 8, 2017)

Yeah they are meant to be flat. That really doesn't look healthy.  Was it on a mount? Or was there some serious tension on that plug?


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## joco-nz (Apr 8, 2017)

Rob - can't see if this was covered in your prior posts.  If so just say and I'll re read in detail.  For the plasma torch, is it using a pilot arc or HF start?  Asking as my little 40amp job is HF and wanted to know if cnc for it on the future was viable or not. I would be looking at a SMALL table, 1m x 1m max size.  But not sure if viable with HF start. Hence the question to draw on your experiences. 

Cheers,
J.


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## rodw (Apr 9, 2017)

joco-nz said:


> Rob - can't see if this was covered in your prior posts.  If so just say and I'll re read in detail.  For the plasma torch, is it using a pilot arc or HF start?  Asking as my little 40amp job is HF and wanted to know if cnc for it on the future was viable or not. I would be looking at a SMALL table, 1m x 1m max size.  But not sure if viable with HF start. Hence the question to draw on your experiences.
> 
> Cheers,
> J.



James, I have this one with a built in CNC port.
http://www.everlast-welders.com.au/product/PowerPlasma_50. 
It has a blowback start. They say the Mesa THCAD can handle HF start. I think HF start might be hard to control noise and may need an earth stake driven through the slab. I think getting up to a 24 volt vs 5 volt system will help fight noise but I have not fought that battle yet. 

I spent all of today rebuilding the bent circuit board and mounting it a bit differently (in a metal electronics enclosure).







its so nice to have a mill when you are doing something like this






Looks like its going to work out OK






And all mounted up






THe LED is just a warning light to say I have 24 volts up there for trouble shooting. It has told me about one problem already..

I am still not sure if this has fixed my problem as I did not have much time by the time I got this done.


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## joco-nz (Apr 9, 2017)

Looking good.

The only thing I would be paying attention to is the level of side forces on that plug. Given the only strength, from what I can see, was from the soldered mounting pins. If you don't already have it a strain relief clamp might be an idea?

 Cheers,
J.


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## rodw (Apr 10, 2017)

joco-nz said:


> Looking good.
> 
> The only thing I would be paying attention to is the level of side forces on that plug. Given the only strength, from what I can see, was from the soldered mounting pins. If you don't already have it a strain relief clamp might be an idea?
> 
> ...



I'll give that a bit of thought. THere is not really any side forces as the DB9 cable is held firm where it exits the drag chain.


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## joco-nz (Apr 11, 2017)

rodw said:


> I'll give that a bit of thought. THere is not really any side forces as the DB9 cable is held firm where it exits the drag chain.



Ok - probably not going to be an issue then.   :thumbup:


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## rodw (Apr 12, 2017)

So i've now got a table!






And here's why I didn't bother to weld up such a precision weldment..






Nice Work from Lee


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## joco-nz (Apr 13, 2017)

Very nice.  Is that TIG or MIG work? If you tell me he did that with a stinger I am going to find a corner and quietly cry.   :hDe:


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## rodw (Apr 13, 2017)

joco-nz said:


> Very nice.  Is that TIG or MIG work? If you tell me he did that with a stinger I am going to find a corner and quietly cry.   :hDe:



MIG, I'm afraid, his TIG is mint too!

Anyway, to cheer you up, I had a go at him today for putting the one [email protected] weld on the top of the machine for all to see. Anyway, I put some of it together, and over the weekend, hope to mount up the gantry.






I am happy with the clearance between the gantry ends and the table, but not the weld! Anyway, a brush with a grinder will tidy it up. This is the first he did then he must have dialed himself in!






Hopefully, it will help keep the rails clean tucked so far back.

Its kinda funny, when I was looking at the gantry ends, they looked too long but now they are assembled, they look correct and in proportion.


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## joco-nz (Apr 13, 2017)

Looking at it in relation to the car ... that's a sodding big lump O steel.


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## rodw (Apr 13, 2017)

joco-nz said:


> Looking at it in relation to the car ... that's a sodding big lump O steel.



And heavy too! I could lift one end pretty easily before I put the linear rails on. I can just lift one end now but at the end where the gantry is parked, I could not really move it much at all. The rail mounting plates were hard to attach on my own as they are probably about 50 kg each. I figure it will weigh in at around 400 kg when done.

The table is roughly 1800 mm x 1800 mm square and the frame is 100 x 100 x 4mm SHS.


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## rodw (Apr 30, 2017)

Its been a while since I updated this thread. There is 2 reasons for that. One is I stuffed up one of the laser cut parts so I had to get it recut before I could make the cradle that holds the slats. And then I found out that Lee had given me the wrong measurement by not allowing for the 5mm steel sides. I had to cut 5mm off each end and still have not got it welded up.

The other reason is I had a small mishap with a milling cutter and a finger on Good Friday.






It was decided this needed to be repaired by a hand surgeon and as I had eaten lunch just before I did this, they waited until 7:00pm before patching me up in theatre.  There is a tendon on each side of the finger and fortunately it went between them both which was very fortunate.

A week later all was well and healing better than the surgeon expected.






Anyway, now it is another week on and I've had the stitches out (about 20 of them not counting the ones that dissolve) and its starting to come good.

I tried to be good by not going into the shed so that left me with the software to work on. So after about 2 weeks, I think I have finally finished the screen interface and connected up all of the signals in the back end.






As I read somewhere, Plasma cutting is really an orphan in the CNC world as its so different to a mill or a lathe. That is because the Z axis is controlled outside of the typical XYZ kinematics model.

I had a starting point for the screen from a LCNC example, but all of the stuff below the screen preview I have pretty much written.   

During this process, I also purchased Sheetcam which is really brilliant for post-processing DXF or SVG files into gcode. It also has nesting capability to fit multiple parts on one sheet of material. With some help from the LCNC forum team, we've modified a GUI interface and added some other components written in C to allow us to use a Sheetcam post processor that has been written to support a commercial torch height control unit. 

I have to say this is right on the bleeding edge of LinuxCNC development because one of the main developers has built an experimental branch that integrates external offsets into the core code. What this means is you can apply an offset that is totally transparent to the LCNC trajectory planner. He clearly had plasma in his sights as he also wrote a component that was aimed at plasma torch height control and built in PID based control along the same lines they do to control servos.

I've written five LCNC support components that allows me to hook up all of the GUI to his experimental torch height control component. I finally solved the problem of accessing the GUI settings from within gcode last night.

A component in LCNC speak is a small snippet of compiled C code that is called on every pass through a thread.  With my hardware, that happens 1000 times a second. You connect various inputs via "pins" in a "hal" text file. "hal" stands for "hardware abstraction layer". This really is a pretty cool software development model as everything remains modular. So for example if your component needs to know the current velocity the plasma torch is travelling at, you provide an *IN*put pin for current velocity and connect the system pin *motion.current-vel* to it in the hal file.

So from the screen dump, you can see there is about 12 LED lights to tell you what is going on and several parameters that can be changed by the user at the touch of a button on the (yet to be purchased) touch screen.  I've actually run out of screen real estate and would like to add a few more controls so I might end up adding a tab in the interface so I can add a few more controls.

Anyway, with a complete GUI and software config, an almost complete table, and a fully configured Sheetcam post processor, it won't be long before this all comes together into a working machine.

Today marks 10 months since I started this project so hopefully, it will be done by the 12 month anniversary.


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## rodw (May 21, 2017)

Its been a while since I updated this build. My finger came good and I brought the fabricated plasma table home so I could keep working on it as it would never happen at work.






And I married up the gantry but it still needs all of the stays fitted to secure the gantry to the gantry ends and I have to wire in the limit switches in place before I can actually do much with it.






I bought a very nice wireless remote out of China






And yesterday I pretty much got it all wired up. THis required quite a bit of reworking of the estop circuits but I think I got it pretty right after yesterdays effort. Sorting out the configuration file took a bit of experimentation as I had no examples of exactly what I wanted to do but I worked it out in the end. 






The pendant has some nice magnetic mounts to store it.






This ended up being a perfect match for my hardware but it took a night messaging China to make sure I had the specs right.






Time has been at a premium and I have not been well so I've  been avoiding the physical stuff and just doing the wiring and software config. I still have  bit of tidying up of the wiring as there is still quite a bit of test wiring there that will be removed eventually.


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## ShopShoe (May 22, 2017)

Rod,

That's shaping up quite well. I'm following and I hope to see a video of it running someday.  Thanks for posting the electronics and programming as well as the mechanics of the build.

I wish you happy healing and I understand as I got myself almost the same finger injury last week and am out of the shop for awhile myself.

Good Luck,

--ShopShoe


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## rodw (Jul 4, 2017)

Its been a while sionce I've done much on this project. 2 more triips to hospital after cutting my  finger did not help.

I ahd a few parts getting powder coated so I sent out my limit switch plates and the levelling feet.
















And I tidied up the drag chain support tray






And I braced up the gantry ends











This one was a bit trickier to squeeze in





And I shortened the Z axis to get more travel.






And started to work on the drag chain






And get all the wires across to both sides of the gantry and attached to the limit switches






And finally, taped a pen onto the torch and drew something!





Then pen was wobbling around a bit but I am happy with the accuracy.

I also put  a dial indicator against one of the gantry ends before I had it all properly braced and was only seeing about 0.05 mm play under acceleration of 1 m/sec/sec so it is well within the 0.1mm I accuracy I was hoping to achieve.

I ran out of time but all I have left to do is to connect the limit switches and sensors to the Mesa control board and  sort out the calibration and config. This will let me home the machine and square the gantry so then I might even be able to cut something!

I also have plenty to do to fit up all of the connectors to the control box as I have not wanted to do this until I knew I had a clear idea of all of the connectors required.


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## rodw (Jul 9, 2017)

Well it been  12 months since I bought my first part but this machine is nearly done. I'm really happy to actually see this machine running Gcode (at 18 metres per minute - 709 inches per minute). I've tested it without missed steps at 21 metres per minute (827 IPM) but I thought it might not be a bad idea to back off a bit.

https://youtu.be/h_7S6iN6-AE

Now its moving, I've spent a fair bit of time debugging and double checking HAL and .INI files. I've done as much testing as I can without cutting stuff. But before I can do that I will have to make sure that I have  a  Sheetcam post processor that works. 

I did find out why people use Ohmic sensing. Here is some 2mm plate during a mock touch off and you can see the plate springing down before the probe triggers and follow the torch up.

https://youtu.be/astf0jqtMrU

My Trafimet torch does not have provision for an ohmic sensor so I drilled and tapped the cup so I can attach a wire as there is now an electrical connection between the screw and the tip.






My torch has a connection to the earth clamp on the plasma in the CNC port and previously I found a relay circuit for a sensing circuit which I've modified a bit so there are a couple of safety interlocks.






So I bought a couple of relays today so I can build this circuit. I am sure the questions will begin now I've got this far and here is the first one.

I think the bottom two 24 volt lines that go to the workpiece and the torch should be from an isolated power supply so there is no chance of blowing up my Mesa 7i76e control card. What is the cheapest and/or best way to to do this? WIll a simple buck power supply off the 48 volt rail do the job or should I get a small DIN rail power supply?


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## ShopShoe (Jul 10, 2017)

Rod,

You have more experience than me, and my electrical/electronic experience is really old-fashioned (relays I can understand.....), but work-a-day functional.

It would seem that a totally separate power supply  would remove all doubt as to whether there is interaction between different parts of the system and would do a better job of keeping the other parts of the system safe from damage. As we used to say building it ruggedly to start and then optimizing it later got things running faster than agonizing over the details endlessly at the beginning.

I am also a great fan of modular design of all types, so having separate modules like power supplies to swap out make changes and repairs easier.

I ramble... I am enjoying this build and thank you again for posting.

--ShopShoe


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## blighty (Jul 10, 2017)

great build, keep the pics coming :thumbup:

may of been answered before....but. is the workpiece earthed from the machine? i ask as my mates plasma has an earth clamp that clamps to the work and when the torch touches the work all hell brakes loose.
stepper motors are earthed to the table. if you have a touch prob, that will earth to the table on contact. plus  the torch will need to earth to find its height. so in my tiny little brain, i sort of think that as soon as the torch lights it will send all the amps/volts and power through everything.


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## rodw (Jul 11, 2017)

blighty said:


> great build, keep the pics coming :thumbup:
> 
> may of been answered before....but. is the workpiece earthed from the machine? i ask as my mates plasma has an earth clamp that clamps to the work and when the torch touches the work all hell brakes loose.
> stepper motors are earthed to the table. if you have a touch prob, that will earth to the table on contact. plus  the torch will need to earth to find its height. so in my tiny little brain, i sort of think that as soon as the torch lights it will send all the amps/volts and power through everything.



Blighty, thanks for the encouragement. Yes I was really hoping I would not need to build the electronic sensor. It is a bit scary when there is 300 volts floating around.

I think it should be OK as long as the sensing circuit is disconnected while the torch is cutting. The first precaution is to use a totally separate (isolated) 12 volt power supply for the sensing circuit. 

I am also using some panel relays to do various things. These are all double pole double terminal ones.






So the relay on the left is the one that turns on the plasma torch. So the second safety precaution is to run the signal through the other side of this relay using the normally closed connections. So when the torch is on, the sensing circuit has to be off.

Then the next step is to tie an output pin to M64 and M65 in the gcode I run. These codes allow me to turn a digital signal on and off. So there is another safety relay (the one on the right). I will call M64 whenever I probe to find the surface. This will trigger the rightmost relay which will connect the wires to the sensing wires on the table and the work piece. After the probing has found the surface, I will call M65 to turn the relay off again.

Finally, I decided to use a solid state relay that I had floating around and I mounted it onto a circuit board tonight with a few other components.






Its purpose is to use the new isolated power supply to trigger the relay when the torch touches the plate. This relay will then switch  my +24v power to a digital input that will tell the machine I have found the surface.

There are several 1N4001 (1000 volt) blocking diodes on this board. Diodes only allow current to pass in one direction.

So here we are a bit tricky. On a plasma machine the earth clamp is actually positive and in our sensing circuit it will be negative. So if for some crazy reason the torch is running while the probe is enabled, the diodes should prevent the current from passing  and destroying anything. Hopefully if it does get that far, it will only destroy the few components on the isolated power supply and not a $500 control board!


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## blighty (Jul 11, 2017)

thanks for you explanation. but i still don't get it. my brain still thinks you going to send all the electron stuff through everything. don't get me wrong, im not saying what you have done wont work, as lots of people have done what you have done and end up with a perfect working cutter. so until i get me head around it, i wont get it.
it's like i could never get my head around how they made tooth picks. i thought the only way they could make them was to get a bit of wood. put it in a lathe and turn it down to toothpick size...... was i surprised
 when i saw How It's Made one night. 

also.... reasone for clearing this up. is i have a tig welder and one job was a seem weld over 24" no filler and had a few to do. thought i could put the torch on the head of the mill, work on the bed etc etc. but didn't do it because as soon as i push the button 150amps would be going through everything................... come to think about it. i could of put some MDF on the table. oh well live and learn.


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## gunna (Jul 12, 2017)

rodw said:


> There are several 1N4001 (1000 volt) blocking diodes on this board.



Rod, 1N4001's are only rated at 50 volts. 1N4007's are the 1000 volt ones.

Ian.


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## rodw (Jul 12, 2017)

gunna said:


> Rod, 1N4001's are only rated at 50 volts. 1N4007's are the 1000 volt ones.
> 
> Ian.



Ian, sorry that was a typo. They are 1N4007's


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## rodw (Jul 20, 2017)

Well, I had a bit of a rethink about the ohmic sensor on a torch that does not have a shield as its the cutting tip that hits the plate so I moved onto other things. I spent a day and a half last weekend soldering up all of the connectors on the case







And an SMA coax connector for the wireless pendant closer to the top of the enclosure.






I had one stuffup that cost me hours trying to work out why the gantry was not homing correctly. Eventually today I worked out that I had accidently plugged the 5V stepper controller wiring back into the wrong  controllers so stepgen 0 n the 7i76e was wired up to joint 1. This was OK except that the home and limit switches were unaffected. so when we homed, the wrong switch was triggered so the wrong motor kept running.

That will be all double dutch to anybody that is not using the new LinuxCNC joint axis homing sequence for gantries. What happens when homing is that the gantry heads towards the homing switches and when the first side hits the homing switch, it waits for the other side to catch up. Once it catches up, each side moves to the specified offset and then home is set. 

The good part about this is that you can home the gantry in software by altering the offsets. In my case, the offsets were different by 2mm between sides to square the gantry.

The problem I had was the wrong side was trying to catchup which did not work very well...  :cry: I only worked it out after I really slowed down the homing velocities so I could see what was going on.

Anyway, If I can massage a Sheetcam post processor, I might even be able to cut something this weekend! But don't hold your breath as I've got a busy few days coming up! 

I also have a couple more wires to add to the cabinet for the 5th axis and a couple more things so I can seal the cabinet up once and for all. None of these are critical for the present config though.


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## rodw (Jul 22, 2017)

Its Alive!

https://youtu.be/zVM5Tz4Tzm4

We had a lot of trouble this morning. I've had the machine torch for 12 months but this was the first time I had plugged it into the machine. The torch came on with the machine and would not go out. Then we tested the hand torch and we could control it from LinuxCNC without having the trigger pressed. So after comparing wiring between the two torches, I cut one  wire inside the machine torch so it looked like there was a switch turned off and everything worked perfectly.Well it sounds simple but the process took several hours of troubleshooting!

I've still got some things to sort out. I'm not sure why the flame goes out on startup. We did edit the gcode a bit and got the outer circle to cut perfectly. 

I was not seeing an ArcOK signal or a torch voltage. I hope it is just a wiring fault in the cable I made up.

I spent about $300 on air fittings in preparation for setting up an engraver but that can wait for a while...

I have so much work to do to set up Sheetcam and work out the right cutting speeds.


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## ShopShoe (Jul 22, 2017)

That's great to see running. I believe you will get the rest of things sorted.

Thanks again for posting this thread and all the details.

--ShopShoe


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## Johno1958 (Jul 22, 2017)

Good to see it up and running Rod. I'm sure you'll get on top of those teething problems .
Cheers
John


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## joco-nz (Jul 23, 2017)

Impressive to see it moving and cutting!   Awesome work.  Teething problems ... pah!   After what you have achieved to date I can't seem them evading you for long.

Cheers,
J.


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## rodw (Jul 23, 2017)

Thanks guys, James, you are right!

I knew nothing about Linux CNC
I knew nothing about CNC in general
I knew nothing about Gcode
I knew nothing about Plasma cutters

But today I managed to cut a donut!






I solved the torch voltage issue by plugging in the connector. What a dope!

Then I found one of the Arc OK signals  had been soldered to a pin in the interconnect cable that was not connected inside the plasma  cutter! I wonder who did that?

Because I knew nothing about my plasma cutter, I did not know that it tries multiple times to establish an arc with a pause in between. So the reason why part of the cut was skipped at the beginning was that I was attempting to pierce too high and the plasma cutter did not get a good arc and turned off and retried just as we were started moving. Lowering the pierce height to 3mm fixed the issue.  

I'm still not convinced I've got the ArcOK signal working properly, but that won't take much to sort out and then hopefully, I can say the wiring is finished. Here's just a small part of it.


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## rodw (Jul 31, 2017)

I did not get much done over the weekend or so it seems

I wrote a small program to make a series of cuts at different speeds 





I started with cuts at 100 mm/min apart, zeroed in on the best looking one and then repeated (several times) at 10 mm/min apart.

So now I have the machine dialed in for 2mm mild steel. As part of this, I told LCNC to log the torch voltage (at 1000 times a second) I kinda forgot about this for a while and the next thing I knew was I had an 8 gb text file!

I also was able to do a bit of debugging of some signals and checked the code for one component I'd written becasue I was only showing  a voltage of about 20 volts. This was due to a software error in my C code. I was only out by a factor of 20. 

I think I need to revisit the calibration resistor in the torch voltage  circuit becasue I think the THCAD board is receiving a  voltage above its full scale range. After fixing my error, the THCAD should have a full scale reading of 320 volts but I think it is getting up around 400-500 volts on startup.

I need to spend some more time cutting while checking some internal signals in LinuxCNC and also with a volt meter. I did debug a bit more of my config. Some of it I did so long ago, I had forgotten how it worked. I'd added a delay on the THC enable signal and I was able to confirm that all of my THC enabling logic (3-4 things must be true before the THC is engaged).

So once I know I've got the torch voltage nailed, I will be able to look at the Torch height control. Once I get this far, I'll be on my own as I have not seen anybody else using the new experimental LinuxCNC branch on a live machine. I really hope it works!


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## rodw (Aug 7, 2017)

I'm afraid nothing much has happened the last couple of weekends Because I did not have the confidence the torch voltage and dividers were correct. So I decided to hack the probes off a cheap set of multi meter cutters and solder them onto the raw voltage output on the CNC port






This let me plug a multimeter in to read the raw arc voltage while cutting






While I was doing this, I fired up halsampler in a new terminal window and it logged the voltage and a few other things 1000 times a second






And something clearly was not right with the voltage divider. So I pulled the plasma cutter apart to access the CNC board so I could change the divider ratio by changing a link on the board which the manual said selected between 16:1 and 50:1.






And nothing changed! Grrr

So I pulled the board out of the machine and inspected it in the sun to find that the manual was wrong! So a few more testcuts later, neither divider was showing correct results.

So I stopped and phoned a friend and I walked down the road to his place and he traced out the circuit for me. Still with nothing definitive I wandered home quite despondent. The next morning, I spent hours analysing the board and drawing out the circuit. Still with no further progress and after thinking about a few things and a bit of research, I decided That the best way to do this was to connect a known voltage somewhere in the cutting volts range to the board and make some accurate voltage readings.

I had a couple of 48 volt power supplies so I decided to join them in series to get 96 volts.






Pretty close, all 17 amps of it!






So I took a deep breath and plugged it in.






And put a high quality multimeter on the raw outputs.






You can see the voltage dropped a couple of volts because of the 100k resistors on the raw voltage outputs to prevent arcing.

So now I could measure the divided voltage






and I could also read the data back in LinuxCNC. I had a discrepancy for a while until I remembered I had a scaling resistor in the cable and I was reading the voltage after it. Sure enough, when I read the voltage before the resistor it was perfect.

Time to do the maths! No wonder I was in trouble. The dividers were out by a factor of 1.5. The 50:1 divider was actually reading 75:1 and the 16:1 one was showing 24:1.

So A quick tweak of the calibration settings in LinuxCNC and I was getting a perfect result within +- 0.7% on the voltage sensing circuit! Finally! So now I can actually get on with setting this puppy up!


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## rodw (Aug 20, 2017)

Well, finally I have got the software working and the THC seems to be working pretty good on the very first cut.






The green line is the torch voltage, the white line it follows is the desired 85 volt  set point and the blue line  on the bottom right is the error which is printed at a higher scale. The beginning of the blue line is where the THC was enabled.


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## rodw (Feb 13, 2019)

Its been ages since I updated this thread. I did get this table pretty well finished





I had a lot of troubles with the experimental software I was running and kinda lost interest for a while. Then I sold the plasma cutter with the intention of buying a Hypertherm XP45. Then I moved my business out of home into an industrial shed with 3 phase power so I thought I'd be better off with a Hypertherm 65 amp machine to cut some of the heavier plate I use.

But then I found a brand new old stock Thermal Dynamics A120 (120 amps) machine earlier this month at a price I could not walk past.






So now I can pierce 16mm thick mild steel!

It took a few days to get it all wired back in and the torch lead fed back though the machine and I was able to tune the machine much better than the cheap Everlast.

So two weekends ago I wanted to get it finally configured so I could cut some parts for a prototype product.

Then everything went downhill due to water in the air lines due to our hot, humid climate. So last Monday week I decided to purchase a refrigerated dryer. But before I purchased it, I read in the manual that you should fit a precooler to the air line in front of the dryer. So I learnt a bit more about precoolers and I found they should be fitted between the compressor and the air tank.

I found some ideas online so I headed off to one of my suppliers to buy an oil cooler for a vehicle and came up with this.






This works an absolute treat! The top pipe is so hot, you can't touch it and the bottom one is cool to the touch! The autodrain at the bottom does remove some water but I think I need to change the pipe work so it sits lower down in a u shaped piece of pipework.

So now the air is cool before it goes through the refrigerated dryer






So the night after I got it all running I did not have the compressor turned of and a seal blew on the motorguard filter mounted to the table earlier in this thread so it ran all night. There was 3 litres of water in the tank but the dessiant crystal on the table were unchanged so I now know not  a skerrick of water gets past the refrigerated dryer. Plus it includes prefilters and post filters on it so I dumped all of the regulators and filters fitted to the table as they are no longer required. I have an auto drain for the compressor tank on order so once it arrives, I'll have the best air setup in Australia!

I've had a fair bit of tweaking in the Sheetcam post processor to get everything running smoothly and I hope I made the last mods this afternoon and I can get on with cutting out prototype parts. Anyway, here is a video earlier this week. 8 mm plate, 80 amps at 1945 mm per minute. There ar 4 holes in the hob but we elected not to pierce each one and instead just cut a line into them to save our consumables when we get to 16mm plate.



So here is the result. an prototype of a bash plate with inbuilt recovery points that makes more room for a relocated swaybar.





Ultimately, these will be cut from 16mm plate and today I bought 1.2m of 16mm and 12mm barstock wide enough to cut these parts out of. With a bit of luck that will be tomorrow's project!

To finish this off, I desperately need to build the downdraft hopper I've designed as it makes an awful mess!


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## rodw (Feb 13, 2019)

I forgot to mention. There are two things to watch in the video. one is about half way through is the shaft joiner hopping around as it tracks variations in the torch voltage. The other thing is the magnetic torch breakaway activating right at the end of the cut. This was because sheetcam chose a really tight spot to start from so when it got to the end of the cut there was no metal there. So the voltage leaps up really quickly so the controller thinks the torch is way off the plate so moves it down and causes the crash. The solution to this is to write a void crossing component for LinuxCNC to disable the torch height controller when it sees the voltage spike. Also in our next cuts, we've created some sheetcam rules that slow the velocity down on holes and arcs. This seems to have made a marked difference to hole cut quality. So much to learn!


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## Scott_M (Feb 13, 2019)

NICE !!!

Looking good Rod. I was wondering about that end shot, it looked like a crash. Thanks for the explanation.  Almost there.

Scott


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## rodw (Feb 13, 2019)

Scott_M said:


> NICE !!!
> 
> Looking good Rod. I was wondering about that end shot, it looked like a crash. Thanks for the explanation.  Almost there.
> 
> Scott



Thanks Scott. That was actually the first crash with this plasma cutter. I had some spectacular ones with the old machine. In this case it was user error becasue I was too impatient to learn how to change the start point in Sheetcam. The previous ones were usually due to poor tuning resulting in oscillations that exceeded the cut height.

Anyway, the issue has been you can't test any stuff for this until you have a working plasma cutter to work with. I had one go at it and failed so I put it aside for now. The solution is track a moving average of the last N readings (N = 10, 20, 100 etc,  I don't know yet) and compare the change in voltage over time (dv/dt). It will probably idle along around +- 100 volts per second and crossing the void might push that to 3000 volts per second or more so it will be a matter of picking a threshold (say 1000 volts per second) that if its exceeded in a positive direction, to hold the height adjustments.

It quite a complex piece of C code to do this as averaging implies a loop but you should not run loops in interrupt service routines that fire every millisecond. But you've just given me an idea to try. I'll add an output pin to an existing component for the dv/dt so at least I can see the issue in real time.


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## Scott_M (Feb 13, 2019)

If you think the code is complex, I'm sure it's waaaay over my head.
Do you have a way to record your real time tracking ? It would be convenient to analyze it after the fact.

Very impressive work so far, I have no doubt that you will get it.

Keep us posted.

Scott


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## rodw (Feb 13, 2019)

Scott yes.
There are two ways. One is to use Linuxcnc/c built in oscilloscope that lets you measure signals every millisecond. The green line here is the plot of torch voltage and the blue line at the bottom is the error (difference between actual and desired volts). The error signal starts jumping around a little bit once the THC is enabled. There is a pink line there which is the ac ok signal back from the plasma cutter which happens near the pierce and the THC is enabled 1.5 seconds later. This is what I've used mostly. Its extensively used to tune servos etc when doing retrofits.





The other way is to use a real time component and a separate program to sample signals every millisecond and write it to a file. I used this to do some regression on torch voltage based on a sample of 16000 readings. It showed a very linear response of 7.53 volts per 1.0 mm with 99.4% confidence on my old plasma cutter. This gave me some real insights into torch voltage behaviour.


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## Scott_M (Feb 13, 2019)

Well that is certainly handy to have "on board" , don't even have to hook it up.  

Thanks for the explanation and now that you mention it I do remember seeing the HAL oscope.  Both of my Tormach machines ( lathe and mill ) run PathPilot which is Linux and I am slooowly getting more familiar with Linux.  It certainly brings out the geek in a person though 

I have confidence in your coding Foo , let me know how it works out.

Being able to pierce 16mm is pretty serious, makes for a robust machine and, it's in house. And nice work on the air compressor.

Scott


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## rodw (Feb 15, 2019)

Well, the 16mm went OK. 1350 mm/min at 120 amps


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## Scott_M (Feb 15, 2019)

Very impressive !

What kind of amperage does it take to do the initial pierce ? Was that 120 as well ? It just blows right through it 

I also noticed a bit of mismatch of the start and end cut. Is that designed ? I wouldn't think  the work moved.

Scott


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## rodw (Feb 15, 2019)

Scott, plasmas are constant current devices so its 120 amps all the way. Some machines can do a soft pierce and ramp up the current during the pierce to reduce the puddle splashing around to improve consumable life but this one has no such control. Yes I had to double check the pierce delay  against the book settings as it was only 0.7 seconds! We probe for the surface, start above the cutting height (pierce height), turn it on, wait for an ArcOK signal from the plasma and then wait out the delay before  commencing the cut.

I'm not sure about the finish of the cut being out. It cleaned up OK. I know I have to rework the torch breakaway as it has some wobble in it. One issue is that the bottom of the cut lags behind the top so its recommended to continue past the start point but when I tried this the THC did not like it so I disabled it. It could be related to that. Overriding Sheetcam's chosen start point so it was away from a corner helped. I've since added a torch off delay of 0.1 seconds so I'll see how that goes.


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## Scott_M (Feb 15, 2019)

Thanks Rod
Also what air psi does this run at and what kind of cfm do you need?   ( just curious )

Scott


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## TorontoBuilder (Feb 15, 2019)

rodw said:


> This thread might take a fair while to develop. Its been 12 months in the making already. My Arduino Rotary table controller project got me interested in CNC but I did not want to do the obvious and convert my mill to CNC. I eventually got interested in CNC plasma cutting and I started about 12 months ago by cramming the electronics into an old Plasma machine case complete with a Torch height control.



Wow rod, I wish I had seen this thread from the beginning. The person I bought my Milling machine from had a CNC plasma machine in his garage. I got to look at it in detail and decided I'd really like one, one day. I wonder if it's worth it for a smaller table size... versus getting 3/8" plate waterjet cut... 

anyway, looks like I will be busy reading about your adventure


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## rodw (Feb 15, 2019)

I can tell you want one! 

You only need about 90-100 psi. This Thermal Dynamics A120 uses 189 Litres per minute (7 CFM). My single phase compressor produces 320 litres per minute (11 CFM) FAD (Free air delivery). This one is a bit old school and has a manual regulator built in and a set of LED's showing the pressure. You flick a switch to enable the air flow and set the pressure based on the LED's to suit the material to be cut then flick back to cutting mode..  That cut was at 80 psi. The Hypertherms control the pressure automatically. I had the compressor and its only new. According to the air shop I got the dryer from its a bit undersized. He said your compressor should have double the air flow of what you need to reduce cycle times.

You do need a source of clean dry air so I think you should add the refrigerated dryer to your shop air.  Some people do use Dessicant dryers and a toilet roll filter (Motorguard filter) right as the plasma. You will save a lot of money in consumables with the refrigerated unit and it has pre and post filters on it so there is no filtering required in your whole shop.

I defnitely need to finish off the downdraft hopper or you could run a water table to catch the mess. There is black dust everywhere!


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## rodw (Feb 15, 2019)

TorontoBuilder said:


> Wow rod, I wish I had seen this thread from the beginning. The person I bought my Milling machine from had a CNC plasma machine in his garage. I got to look at it in detail and decided I'd really like one, one day. I wonder if it's worth it for a smaller table size... versus getting 3/8" plate waterjet cut...
> 
> anyway, looks like I will be busy reading about your adventure



John, There are plenty of small tables out there. You have to be sure you can get plate steel cut down but you can cheat like I did with flat bar. for 3/8 you could get by with a 45 amp plasma cutter. Hypertherm 45XP or Thermal Dynamics/ESAB A60i. Here  we'd use a laser cutting service for that job. It should be cheaper than waterjet. The side rails on my plasma cutter were laser cut  from 12mm (1/2") to get exact hole positioning and the M6 holes came back ready to tap but the M4's they etched for position and I had to drill them. Thinner material will let them cut holes ready to tap down to M4 though.

I will say that a plasma table sounds simple enough but in hindsight its probably not ideal for your first CNC machine unless you purchase an external torch height control. But I think what I've achieved in software is superior to what the external controllers can achieve and the voltage sensing board was only USD $69. What I did not understand was that plasma support was not well supported in LinuxCNC (as its kinda an orphan CNC process) but since I started its come ahead in leaps and bounds with several projects on the forum which are bound to get good plasma control into the base source code soon. There is a more complete build here https://forum.linuxcnc.org/show-your-stuff/32029-rods-spaceship-scratch-built-plasma-cutter-build


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## rodw (Feb 15, 2019)

John, also the plasma spider forum is a good source of info. I weakened and put a briefer build thread there too
https://plasmaspider.com/viewtopic.php?f=103&t=22826
But the forum is very Mach3 oriented. They have no idea what we've been able to achieve in LinuxCNC... Stuff that leaves the commercial software for dead.


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## Scott_M (Feb 15, 2019)

Well of course I "want" one !

But I do not have the room for anymore stuff in my shop 
If I do end up with a bigger shop, my compressor should handle it. I have a 70's vintage LeRoi-Dresser 400 series it is spec'ed at 23cfm at 175psi. And I just rebuilt the pump a couple years ago.
I do a lot of sandblasting and needed the cfm.

Scott


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## Johno1958 (Feb 20, 2019)

Some serious cutting there Rod.
Great machine.
Cheers
John


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## rodw (May 14, 2019)

Well its been a while since I updated this thread. Once I upgraded the machine, I needed to do 2 things. Add a larger drag chain for the larger torch cable and also to install ohmic sensing to sense the material height more accurately than my float switch.







The plasma cutter came with a clip to connect a wire to the torch shield. Note this is not the actual electrode tip but a protective shield that is isolated from the arc voltage.




The Ohmic sensing took a lot more work than I expected as it required a seperate isolated power supply and a three optoisolated relays. 2 of these isolate the probe circuit while cutting and the third switches field power to an input n my Mesa 7i76e when the torch touches the material. I also added a small circuit board  with some protectivediodes and some LED indicators which are now redundant as the relays have LED on them anyway!




I've spent a fair bit of time with some plasma enthusiasts in the Linuxcnc movement working on a new plasma controller written by Phill, a fellow Aussie. He has been amazing with the features he's added from feedback by people like me and there is now no point buying a commercial controller as this is that good and very easy to install.





Whats so unique about this config  called Plasmac is that all control is built into the GUI so the plasma cutter just receives a M3 command  to start and all probing and torch height control just happens. I have not shown it here but on the Plasma Run tab, I have  a list of about 50 cut charts that can be selected from G code or by walking up to the machine and choosing your material from a dropdown. It also has a Statistics tab which tracks the number of piercings and distance cut so you can monitor consumable life or gather data for quoting purposes.

Today I wrote a Sheetcam post processor which found a lack of error checking and while I was workin on the Post, Phil added some clever error checking that  checks for invalid tool selection in G code before a cut is made. (Which you can see in the screen dump)

But proof is in the pudding. Here is a part I cut yesterday on a steeply angled bit of material and it had no trouble following the material at the 2mm cut height I was working to just be reading the arc voltage and using a PID loop to control height. 





In the next post I'll add a couple of videos but it looks like its about time plasmac did the obligatory cutting of a sheet of corrugated iron!


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## rodw (May 14, 2019)

So here is a video cutting the part on the slope.


And a bit of a walk around my machine


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## wrljet (May 14, 2019)

Do you have a link to the Plasmac controller?


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## rodw (May 14, 2019)

wrljet said:


> Do you have a link to the Plasmac controller?



Yes, on the very first post on this thread there is a link to the repository on github
https://forum.linuxcnc.org/plasma-laser/35449-another-plasma-component?start=0

There are some instructions on how to install it on this thread I wrote
https://forum.linuxcnc.org/plasma-l...a-complete-thc-plasma-config-for-any-hardware

Recommended hardware is a Mesa 7i76e ethernet board and a Mesa THCAD voltage interface but it will work with external hardware like the Proma. You can get that here or from Mesa direct.
https://mesaus.com/

It currently requires compiling LinuxCNC from source and I recommend that you start with one of these ISO's (probably the latest AMD64 one for 64bit hardware)
http://www.linuxcnc.org/testing-stretch-rtpreempt/

The main reason why it requires compilation is that its included the reverse run branch that is not in the core code and Phill has added it to his repository. This lets you step back and forward through the gcode when paused which helps with error recovery if a flameout occurs. Eventually, I think this will become a part of the linuxcnc core distribution as we are now just tidying up the last few things including a Sheetcam postprocessor I finished writing yesterday.


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## rodw (Jul 1, 2019)

Just an update here. our plasmac plasma config has made it to the master branch (v 2.9) of linuxcnc and its documentation is available here:
http://linuxcnc.org/docs/devel/html/plasma/plasmac-user-guide.html


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## Scott_M (Jul 2, 2019)

Very Cool !!

I know it has been a lot of work but your results are outstanding. Thanks for your efforts, kind of makes me want to build one 

Scott


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## rodw (Jul 13, 2019)

Scott_M said:


> Very Cool !!
> 
> I know it has been a lot of work but your results are outstanding. Thanks for your efforts, kind of makes me want to build one
> 
> Scott



Well a good start would be to read the Plasma Primer I got conned into writing for Linuxcnc
http://linuxcnc.org/docs/devel/html/plasma/plasma-cnc-primer.html

For some reason, I never got an email notification of your post.


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