# another 4th axis...... and a 5th



## blighty (Mar 9, 2017)

i have some jobs coming up that could really do with a 4th axis. my cnc controller box is already geared up for a 4th and 5th axis, and with the advent of fusion 360 making its self free to all hobbyist (thanks Autodesk) it is now possible to run a 5 axis mill.

so i have been hitting the numbers to find out gearing between the stepper and the table. i know that normal rotary tables are 90:1 that would be great, but they do suffer from backlash. this can be made to a minimum but you will still have some. next option would be timing belt. problem with that is your now down to very low gear ratios e.g 6:1 other wise pulleys tend to get big. next is antibacklash worm drive. this will now put us back up to the 90:1 plus. and the last one is the harmonic drive. no backlash, high ratios....... not cheap.

it seems that the easiest option would be belts and pulleys. that then brings up the gear ratio. if you take the step of the motor, plus microstepping divide it all by 360 etc etc. and make the gearing 3.6:1 (20t:72t pulley) for each step you will get 0'3'0 deg. this works out well. but  if your part has a 4"rad and you machined at 4" you would get a flat that is 0.12mm wide at each step. on an 8 inch part would this really be a problem? depending on space i could go to a 144 tooth pulley or up the micro step count.

as this one day will sit on top of a 5th axis both 4th and 5th should really have the same gearing and all sit in a compact design.

I have all the gear i need to build it now, as in steppers and controllers so it should be a quick build 

thoughts??


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## dnalot (Mar 9, 2017)

Hi

I fretted over the same problems when fitting a 4th axis to my CNC router. I finally just dug very deep into my pocket and bought a zero backlash gearbox that fit directly to my stepper motor. Works great but expensive if you can not find a used one like I did. 

Mark T


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## blighty (Mar 10, 2017)

do you have any more details on your gearbox? would be worth looking into.


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## rodw (Mar 11, 2017)

Having fitted a stepper to a 90:1 rotary table, I found that you can't get much more than 4 rpm out of the average stepper motor. I think a 5:1 timing belt drive with a good microstepping drive would do the trick. My DM542A stepper drive does 25x microstepping on my plasma table under LinuxCNC and it only cost about $30. Thats 5000 steps per rev so the resolution would be about 52 seconds when I eventually add a rotary axis. Surely that is enough?


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## blighty (Mar 12, 2017)

rodw said:


> Having fitted a stepper to a 90:1 rotary table, I found that you can't get much more than 4 rpm out of the average stepper motor. I think a 5:1 timing belt drive with a good microstepping drive would do the trick. My DM542A stepper drive does 25x microstepping on my plasma table under LinuxCNC and it only cost about $30. Thats 5000 steps per rev so the resolution would be about 52 seconds when I eventually add a rotary axis. Surely that is enough?



think your right about 52 seconds being enough, but it would all depend on the diameter of what your cutting. im thinking of making the table 8" so i can work thinks out from there. was also thinking about the step count. as in what does it do when there is a measurement thats in between your step count. e.g you can only get 1deg per step what happens when one day you need 1/2deg step.


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## blighty (Mar 12, 2017)

had a play with some numbers.

i was a bit out from what i said before. if you have a stepper stepping at 10miro steps with a gearing of 3.6:1 you will get a step of 0.05deg (0'3'0)
that would mean if you took a cut then did one step took another cut, over a 4" rad you would get a flat of 0.088mm (0.0034)
had a look at the micro stepping values my driver can do and one of them is 50. so doing the same cut you now get a 0.02mm (0.00078')flat and 0.01deg (0'1'12)
would be nice to get rid of the '12. considering you probably get 0.1mm and more in head deflection, dont think 0.02mm over 8 inches is nothing to worry about.


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## ninefinger (Mar 12, 2017)

This is interesting to me as I've fabricated a stepper motor adapter to my 6" rotary table but I have yet to use it...(insert excuse here), though I did generate some G-code from Fusion 360 to try it out.

I have the typical 90:1 reduction - 1 deg = 50 full steps (1/4 turn on stepper / input). 
But the driver I currently have is typical of the cheap ones($15), micro stepping by the power of 2 (1 2 4 8 16 or 32 micro steps).  I'm going to try the 32 micro steps and see how it does, as a smaller resolution may be of more benefit than speed - time will tell.

You are probably right that the absolute distance of each step at the 4" rad isn't critically important though small is nice. 
I think that - depending on your controller - having a small "exact" number of degrees per step would be the desirable configuration, so that there is no rounding error when the controller is calculating the moves, though not being a mathematician or programmer I could be wrong and there are other ways of calculating angles (rads, etc) and cumulative moves that may be in use behind the scenes to accommodate error stack up.

I use LinuxCNC and the rotary axis motion is defined by degrees (default / my choice).

I think it also has to do with the CAM software and the post its using for the controller and the rotary axes, though I would think most will output degrees. 

Do keep us informed of your progress.

Mike


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## blighty (Mar 13, 2017)

ninefinger said:


> This is interesting to me as I've fabricated a stepper motor adapter to my 6" rotary table but I have yet to use it...(insert excuse here), though I did generate some G-code from Fusion 360 to try it out.
> 
> I have the typical 90:1 reduction - 1 deg = 50 full steps (1/4 turn on stepper / input).
> But the driver I currently have is typical of the cheap ones($15), micro stepping by the power of 2 (1 2 4 8 16 or 32 micro steps).  I'm going to try the 32 micro steps and see how it does, as a smaller resolution may be of more benefit than speed - time will tell.
> ...



using Mach3 at the mo, and with mach like LinuxCNC you can ether run the 4th in constant mode or step and dir. 1 unit is taken as 1 deg. have found a thread on how to change the post possessor to get mach to work with Fusion 360 and 4th axis. not found one with 5th yet.

i'll get the sizes of the pulleys i need and draw it up. would be nice if i could lay the stepper on its side but that would mean having a 90deg twist in the belt. at the mo it will be about 5.5inch think. that's from the bottom to the top of the 4th axis table. 

as for bearing to support the shaft, was thinking angular roller near the work end and a plane bearing with thrust race the other, but may go for roller both ends, or i could............:wall: its never easy is it :wall:


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## rodw (Mar 13, 2017)

Blighty, I will be very surprised if you can get up to 50x microstepping. There are a lot of other timing issues that will impact and limit speed in the real world. 

In my instance, I have dedicated hardware step generators on a commercial quality external ethernet control card (Mesa 7i76e) able to run at 10 Mhz and the best I could get was about 90 kHz with 40x stepping. I did shorten the step time to see if I could squeeze a few more pulses in a second but never tried to see If I could push it past 40x. Also be aware that there is a limit to how much accuracy microstepping can add so you can't really assume that you have microstep resolution. Thats why  Gecko does not do more than 10x microstepping with their stepper drives. What you do gain (with good quality microstepping controllers) is a much smoother motion.


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## blighty (Mar 13, 2017)

rodw said:


> Blighty, I will be very surprised if you can get up to 50x microstepping. There are a lot of other timing issues that will impact and limit speed in the real world.
> 
> In my instance, I have dedicated hardware step generators on a commercial quality external ethernet control card (Mesa 7i76e) able to run at 10 Mhz and the best I could get was about 90 kHz with 40x stepping. I did shorten the step time to see if I could squeeze a few more pulses in a second but never tried to see If I could push it past 40x. Also be aware that there is a limit to how much accuracy microstepping can add so you can't really assume that you have microstep resolution. Thats why  Gecko does not do more than 10x microstepping with their stepper drives. What you do gain (with good quality microstepping controllers) is a much smoother motion.



as i said.........:wall:its never easy:wall:

in that case ill have a play with a stepper at 50 micro and see what happens. i remember increasing the step count on me lathe. i didn't run a job, was just seeing what it would do. from what i remember it got smother, quieter and a lot slower the higher you went. would start skipping steps if you went to fast. if you kept the speed down it was fine, but saying that and as i didn't run a job i have no idea how accurate it was.

i've just put in order in for the bearings. was about to order the belts a pulleys. then i saw your post. i'll hold off till i have a play. but again, saying that if the stepper is just sitting there i wouldn't  know if its keeping position. i could rig something up on a surface table with some sort of flap on the stepper. clock up the flap, spin the stepper at various micro steps, speeds and see what happens.


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## Blogwitch (Mar 13, 2017)

Would one of these be suited to what you are trying to achieve?

https://www.aliexpress.com/item/CNC...2754624050.html?spm=2114.01010208.8.21.lErvVE

The table can be removed and fitted with a 100mm chuck.

John


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## blighty (Mar 13, 2017)

Blogwitch said:


> Would one of these be suited to what you are trying to achieve?
> 
> https://www.aliexpress.com/item/CNC...2754624050.html?spm=2114.01010208.8.21.lErvVE
> 
> ...



that's exactly what im after. good find shame its in the US $416+ import tax  + cos we can tax tax. 700 quid later....

like the design. worth looking at dim's see if i can come up with something similar.


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## Blogwitch (Mar 13, 2017)

The one I pointed to, with postal charges and 20% import duty from China should come to just over £400 to the UK.

I got a 5" 6 jaw chuck from AliExpress for £140, and only had to pay £4 import duty, so the above price could be cheaper.

There are hundreds of this type available from AE, some with chucks, some without, all about the same price.


John


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## blighty (Mar 13, 2017)

blogwitch....

sorry i should learn to read stuff... well all of it anyway. i just saw the US bit amused it was from the US. dont tend to get stuff from the US as they cant seem to make up the mind how much to charge. i spent 50 odd quid on some bearings from the US and got stung 48 quid. someone sent me a pulse jet to fix 140 to send it 60 odd quid get it.


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## Blogwitch (Mar 13, 2017)

BTW, if you go down a little on that advert, it shows all the basic dimensions of the item, it is not as small as it looks.

John


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## rodw (Mar 14, 2017)

Blighty, When I did my tests I used a cheap $10 tacho off ebay to measure RPM of an unloaded stepper. You can calculate the RPM and compare with what you measure to see if you are missing steps. Once I hit the limits, I backed off a bit.


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## blighty (Mar 14, 2017)

looking at the table blogwitch posted. one axis has 8:1 the other 6:1. i  have seen a lot of 4th with 6:1. may be there is something about 6:1  that gives you the best of both worlds. or it could be a case of "well  that guy did it, so will i" kind of thing.

if you go with 6:1 you  get 0.03deg per step. opposed to 0.05deg @3.6:1 going by that i would  need a 20t and a 120t. HPC gears stop at 84t at £69 (http://www.hpcgears.com/pdf_c33/12.72-12.77.pdf). i could make my own  pulleys.... hang on don't you need a 4th axis for that:wall:


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## Blogwitch (Mar 14, 2017)

Try here, about the cheapest you will find plus they do large pulleys as well.

http://www.beltingonline.com/

Here are the two that you wanted

http://www.beltingonline.com/20-tooth-mxl-plastic-pulley-pp20mxl025m-11490

http://www.beltingonline.com/120tooth-mxl-plastic-pulley-pp120mxl025m-11509


John


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## blighty (Mar 14, 2017)

Blogwitch said:


> Try here, about the cheapest you will find plus they do large pulleys as well.
> 
> http://www.beltingonline.com/
> 
> ...



call me a snob, but not to keen on plastic pulleys, but they do have  selection of ali ones


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## Blogwitch (Mar 14, 2017)

Unless you are trying to swing your mill around the stepper motor, then plastic will be just fine.

Why spend 10 times the price on a metal one that a plastic one will do the job just as well?


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## ninefinger (Mar 14, 2017)

Plastic, metal rubber - as long it works.  I'm using large plastic pulleys (80T) on my cnc mill conversion (have a small aluminum hub), been fine for years.  The belt is rubber.  Don't get caught up in flash and bling for something that doesn't need it.
Another way of thinking - if the rubber tooth can transmit the load why not a plastic tooth?  There are better things to spend money on (like tooling!)
Mike


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## blighty (Mar 14, 2017)

im going for ali pulleys 'cos i like shiny things
	

	
	
		
		

		
			





all the bearings turned up today and i have been going through blogwitch's website he posted. need to give them a buzz tomorrow as they don't stock the 120t pulley you have to phone and ask for them. i have decided to go for 6:1 gearing as it seems a lot of other people use the ratio on there home build. even manufactured 4th axis (ebay ones, not HAAS) use 6:1.


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## Blogwitch (Mar 14, 2017)

I should have added 'while you are prototyping'.


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## ninefinger (Mar 14, 2017)

One of the considerations you haven't mentioned is what you will be machining.  This will drive the consideration of holding torque and moving torque.
You don't get a torque multiplication effect of 6:1 though with this setup unless you are machining at the very center of the table.  Inside the diameter of the large pulley you'll have a torque multiplication effect to the stepper, the closer to center the closer to the 6:1 ratio. Outside it you'll be reducing the effective torque.  At your above mentioned 4" radius/8" diam (~200mm diameter), the torque reduction will be very pronounced. 200mm working radius:77mm pulley =   2.6:1 effective torque reduction.
Those Aliexpress tables tend to advertise 'engraving', as machining hard materials or taking significant cuts would probably cause the steppers to loose steps.
A workaround is to use very small diameter cutter to keep the forces down - i.e. no hogging or taking big cuts with a facemill. You'll probably need to keep the cuts small anyways due to loss of rigidity with all the joints and suspended working platform.


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## Wizard69 (Mar 14, 2017)

blighty said:


> call me a snob, but not to keen on plastic pulleys, but they do have  selection of ali ones




I have mixed feelings about plastics myself but the newer resins can produce pulleys and gears as good as aluminum.


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## rodw (Mar 15, 2017)

Blighty, if you are in the UK, maybe also look at RS Components I've bought a couple of pulleys from them and they were reasonably priced. T5 is a metric size (5mm pitch). My stepper reduction drives are using a 5M belt which is similar to T5 except the grooves are rounded and are meant to have longer life and less torque loss. I'd never heard of them before until IO bought these reduction drives. I think it is a pretty new standard. I'm sure the belts will be hard to find when the time comes to replace them.


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## blighty (Mar 15, 2017)

ninefinger said:


> One of the considerations you haven't mentioned is what you will be machining.  This will drive the consideration of holding torque and moving torque.
> You don't get a torque multiplication effect of 6:1 though with this setup unless you are machining at the very center of the table.  Inside the diameter of the large pulley you'll have a torque multiplication effect to the stepper, the closer to center the closer to the 6:1 ratio. Outside it you'll be reducing the effective torque.  At your above mentioned 4" radius/8" diam (~200mm diameter), the torque reduction will be very pronounced. 200mm working radius:77mm pulley =   2.6:1 effective torque reduction.
> Those Aliexpress tables tend to advertise 'engraving', as machining hard materials or taking significant cuts would probably cause the steppers to loose steps.
> A workaround is to use very small diameter cutter to keep the forces down - i.e. no hogging or taking big cuts with a facemill. You'll probably need to keep the cuts small anyways due to loss of rigidity with all the joints and suspended working platform.



good points to bring up.

i tend to cut Ali and brass with the odd mild steel thrown in there from time to time. more so with the steel as i have just started a 2" Burrell build. 

for the time being, cuts will be cut on the light side. any holes that need drilling away from the center will be done at 33mm/min and not the normal 140. at a later date I will be putting some form of disk brake on the axis's. controlled by a pneumatic piston.


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## blighty (Mar 24, 2017)

a quick up date.

after a week or so of trying to sort some pulleys out...... was trying to get 20 /120 tooth pulley. no one seemed to have the 120 in stock, so had to be made. one of the quotes i got was £195 each. so i finally went for 15/90tooth. price cam down to 70 odd quid all in. should turn up middle of next week.


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## blighty (Apr 17, 2017)

few weeks later................bits have turned up. not really what i was expecting. thought they would be Ali, but their  made of steel and a bit on the heavy side.
the 90mm pulleys have cam locks, one of the 15 tooth has a 6mm hole in it and the other just has a pilot hole, but both need an 8mm. 

i'll have a play over the next few days see what i can come up with. thinking about making the 4th axis first. with a means of fitting it to the 5th axis when needed.


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## blighty (Apr 25, 2017)

stupid ruddy cnc!!

started to machine up the top plate for the 4th axis. needed to cut 177mm x 223.35mm (stupid size i know) Y axis travel is 182mm minus the 12 mm cutter
just had enough to make the cut, but a bit on the risky side. so i changed to a 10mm cutter to give me a bit more room. still a bit risky. then thought i would change the size from 177mm to 170mm that should give me loads of room.....hit the button and off she goes. it does all the inner work fine, takes the first pass around the out side all fine, takes another pass, still looks ok. looks like a got away with it. meanwhile the swarf is piling up on the Y way cover so on the 3rd pass the Y jams up, stepper jumps about a million steps into the work........... C**K IT!!

so started with 177mm end up with 168mm :wall:

need a bigger mill.


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## blighty (Apr 25, 2017)

well that took longer than i thought it would, next thing is the shaft. 

random pics.


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## blighty (Jul 17, 2017)

not been in the shed for a bit, but just had to weeks off and its not 32deg in the shed, plus I got a massive fan

few weeks back (before it got hot) i made the shaft for the 4th axis. used the Myford MG12 for the first time in anger. well happy with the results.

have made all the side to the box that holds all the stuff in. turned out a bit bigger than i thought it would, might not  as compact job as i first intended. for the 5th axis will have to go for the traditional trunnion type. also had a bit of a problem fitting the stepper. if i had of made the box an inch longer it would of been fine, but had to machine out a lot of one of the sides so the stepper could fit in there. then had the trouble of mounting it. 

as i said the box is all made, screwed, doweled in place then squared up. sorted the wiring in the control box and set up Mach. turned it all on, hit the button..................and nothing happened:wall::wall::wall:
wont bore you with the details, but 2 hours latter it works:thumbup:


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## blighty (Jul 18, 2017)

started on the plate last night, faced off the back and board the hole for the shaft to fit. plate is 160mm dia. 15mm thick. 

to night i will put it on the mill, pick up the 8mm hole and drill the clearance holes so the plate can be mounted to the shaft. once on the shaft, put the assembly in a 4 jaw, clock it up and face of the face and turn down to 160mm dia. then figure out how to hold a chuck on it.

not to sure if i'm going to put T slots in the plate and threaded holes all over the place. might do that at a latter date.


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## blighty (Jul 26, 2017)

it's all up and running 
had a few problems mounting the thing to the bed of the mill. in all the excitement of making a 4th axis i some how forgot to build in some way of clamping the thing to the bed:wall: as luck would have it there is enough room inside to slide two 12mm threaded rod through the body with a nut on top to clamp it down to the table...... that was lucky. a few things turned out to be lucky with this build. if you lay it down in lets say 4th axis mode the center of the axis is in the middle of the Y axis travel. when used in 5th axis mode its about 5mm of center, so still lots of Y travel, but also when the 5th axis is 90deg the chuck will be just out side the Y axis travel so i should still get all my Y travel.

other problem i thought i would have and ended up with....... the plate that holds the chuck is 160mm dia. the bits that holds on to it (the shaft) is about 50mm. when something is in the chuck you can bend it from side to side and you can see the 160mm plate moving. found a big needle roller thrust bearing. I will fit this between the body and the plate, leaving  a few thou on. so when you tighten the plate up it should squeeze the thrust  bearing and support the plate on the outside edge.


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## blighty (Aug 10, 2017)

done some more work on the old 4th the other week, machined up the plate to fit the needle roller thrust bearing. thing the thickness of the bearing was about 5.something mil. so i machined to a depth a bit less than that. first to allow for the 0.2mm gap between the plate and the body of the 4th. and a bit more so when you tightened up the plate to the shaft it would pull the plate down onto the bearing.this seems to of taken out all the play that i was getting. so now all you get is a bit of flex in the material it's self. will have to look for a tail stock for long peaces.

as for setting up mach.......
did all the calc's for the step per unit. came out at 33.33 steps per deg. tried this and it never got back to zero it was all ways off. so if you pressed  the "zero all" button, the 4th axis would go from 359.999deg to 0.009. zero again and it would go to 359.992 and so on. would never go back to 0. so i started playing with the step count..... this went on for a bit (kinda like this post) ended up with 33.3333333333333333333333333333333. problem solved 

just have to think of something to make with it now.


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## jeep534 (Sep 7, 2017)

This is all very cool 
pictures of it on the mill please 

Happy Hunting
archie


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## blighty (Sep 10, 2017)

best i can do for the time being.


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