Enco (Rong Fu RF30) Mill/Drill Conversion

[mnay]

Chuck,
Thanks for taking the time for such a detailed response. It was very helpful and I believe I have about figured out what to do. What started this is a friend gave me a couple of stepper motors and drivers and I have always been interested in cnc at home for my hobby projects. My used mill came with ball screws already installed so I have a little bit of a place to begin. Now to convince my wife to let me spend the money. I will probably just buy a piece at a time and work at it.
Also I want to be able to loosen the belts and back the cnc away and use manual if I need to. I liked the brackets you made for your steppers. I will do something like that.
Thanks again,
Mike

 

[cfellows]

Mike, I forgot to mention that Home Shop Machinist magazine featured a multi-part article on converting a mill / drill to CNC. I had found it to be interesting and helpful even though it was published starting in May 1990. Hardware hasn't really changed much since then although it has gotten cheaper, thanks to the Chinese!

I would definitely encourage you to move forward on the conversion. You'll be sooooo glad you did. It's really fun and interesting to see what you can do.

If you've already got your ball screws installed and stepper motors on hand, you've got a real good start. From a budgetary standpoint, this Stepper Controller is a lot cheaper than the Gecko G540:

http://www.ebay.com/itm/221464800449?_trksid=p2059210.m2749.l2649&ssPageName=STRK:MEBIDX:IT

I'm starting a CNC Router Build and bought this controller to use with it. I've read mixed reviews on it, but at that price, I figured I'd give it a try. For the software, you can download a free version of Mach 3 and use it indefinitely as long as your g-code file doesn't exceed 500 lines. It also has some built in wizards that let you cut profiles, pockets and drill holes without the need for CAD or CAM software. And, if you can write your own g-code, you can do some pretty neat things in a lot less than 500 lines of code. All this will let you get started with your CNC machine and buy or upgrade the software later.

Chuck

 

[mnay]

Chuck,
Thanks again for your time. I will keep you posted on my progress and may have a few more questions along the way.
Mike

 

[mnay]

Chuck,
I looked like you made your own timing gears/sprockets. Is there a certain type of belt that I need to use? Sources?
Thanks again, Mike

 

[mnay]

I have done some more research on my own and found several sources for belts and pulleys. They are quite expensive. I can see why you would machine your own. I may buy one for a sample and do the same.
I have purchased a breakout board and am building a power supply for the steppers. I will post some pictures when I have something to show.
Mike

 

[RonGinger]

Give serious thought to using a direct shaft connect, no belts or pulleys. Look at a modern machine, like a Tormach and you will see that is what they did. Before the modern hi torque steppers pulleys were needed to get some torque boost, that is not the case now, particularly on a small machine. The only reason for using belts is when you need to get the motor into a position to keep it out of the way.

I would also stay away form those ebay driver boards, they are really poor drivers. When you are spending several hundred dollars on a project you will soon forget you saved a few bucks on a driver when you get less than the best performance.

 

[cfellows]

Mike, sorry, I hadn't visited this thread for a while and didn't see your question regarding the pulleys. The pulleys and belts are the XL series which are 0.2" pitch. I've bought pulleys and belts on EBay when I could find them at a reasonable price and I've made them. The cutter is made froma 2" x 3/32" thick slitting saw.

If you do a Google search on XL timing pulley dimensions, you'll find lots of diagrams showing the tooth profiles, depth, and pitch diameter. I made this cutter a number of years ago and as I recall, I just mounted the cutter in the lathe and used a tool post grinder to bevel the sides of the teeth with the cutter spinning. There is no side rake or clearance on the teeth, which is not ideal, but it works OK for cutting aluminum pulleys. A suitable fly cutter with proper rake and clearances could be made quite easily and would also be fine for cutting aluminum. Belts are sometimes available in the right size from Ebay or you can get them from Mcmaster and Grainger. Stock Drive Products also has about any size you need, but their shipping costs tend to be prohibitive.

Ron, I used pulleys and belts on my machine because I didn't want the motors, which are pretty long, sticking out so far from the machine, particularly in my rather cramped workshop. I also felt like I needed the extra torque of gearing them down since my Nema 23 steppers may not be quite beefy enough for direct drive. It also makes it easier to use the machine manually by just removing the belts. Nema 34 would have been more suitable, but the jump in cost is considerable, not just for the motors, but the larger power supplies and stepper controllers needed for the higher amps.

Chuck

 

[mnay]

Chuck,
No need to apologize, I realize people are taking their time to answer lots of questions from me, but it is appreciated. Thanks for your advice and the many threads we learn from. I will let you know once I make some progress worth reporting. Still in the parts collecting, learning stage.

Ron,
Thank you for you input. I agree with you completely that to have a quality system I will need to spend the money. I am having to experiment on the cheap for now, because of budget. What started me down this road is that a friend upgraded his Tormach mill and gave the the old style steppers and some micro step drivers. I believe they are probably powerful enough to direct couple and I believe I have figured out how to do that and still use my machine manually. I am putting these on a bridgeport size mill that I pieced together over the years and it also happens to already have ball screws installed. I my bother you folks with more questions as I go. I am building a 48v power supply right now.

Mike

 

[Swifty]

I don't know much about conversion to CNC, but I assume that most motors have minimum step of 1.8deg, which on a .200" per rev leadscrew is .001" per step. If you gear it down, say at 2:1 ratio, won't this allow a movement of .0005" per step, as well as help with more torque? I've been thinking about making a CNC mill, just seem to prefer direct drive.

Paul.

 

[blighty]

I don't know much about conversion to CNC, but I assume that most motors have minimum step of 1.8deg, which on a .200" per rev leadscrew is .001" per step. If you gear it down, say at 2:1 ratio, won't this allow a movement of .0005" per step, as well as help with more torque? I've been thinking about making a CNC mill, just seem to prefer direct drive.

Paul.

all correct. but there are pros and cons to all.... i wouldn't go with belts on a stepper but i would for a servo. i wouldn't gear down a stepper but i would a servo and so on.

if you do gear down a stepper say 2:1 you would be right in saying you would double your torque and half your resolution, but you will also half your rapid speed. to get your resolution back..... most if not all drives have micro stepping, so the drive will split 1 step of a stepper (1.8deg) into 10 for e.g. now you have a stepper doing 2000 steps per rev or 0.18deg per step. this in turn opens up another can of worms over torque issues.

using belts is another place where backlash can creep in. if you do need to gear down to get more torque, put bigger steppers on it. then the cost will go up, but will the cost of a bigger stepper out way the cost of pulleys, belts, mounts and time and effort in making it all.

there are lots of options all depending in what YOU want out of YOUR cnc mill. you just need to find what you need to fit your requirements...... then add 30% to it.

 

[Swifty]

I can understand the problem with backlash, the more bits, belts and joins you have could be a problem. I'm still in the process of trying to understand all the controls needed, drivers etc and how they work.

Paul.

 

[cfellows]

I just upgraded from 24v DC to 48v DC. It's improved my rapid speed to a reliable 30 in sec. I don't think it should have any affect on holding torque or cutting speeds, the latter being more a matter of material and depth of cut.

I don't think the timing belts on my machine introduce much if any backlash. My mill has about .003" backlash on each axis and some, if not all of that may be the ball screws.

 

[blighty]

30 inch a sec ????? you sure about that

good with the volt change. when i did mine the norm was to take the rated volts of the stepper and times it by 20 to 25 and that was it.

3tho backlash not bad for a home build. i have a bit of backlash in mine, seems to be coming from the fixed end bearings. not much point in getting rid of it as the deflection in the column is more than the backlash.

 

[cfellows]

30 inch a sec ????? you sure about that

Guess I meant 30" a minute!

 

[Pertsa]

Hello!
Here is my version of rong fu 30 cnc. Z-axis is made also with ballscrew. I have solidworks 3d files of z-axis, if somebody wants them, I can upload these to download area.

 

[barnesrickw]

If you had meant 30"/sec, I would have said you're Rong Fu. 😃

 

[Len-Tikular]

Hello!
Here is my version of rong fu 30 cnc. Z-axis is made also with ballscrew. I have solidworks 3d files of z-axis, if somebody wants them, I can upload these to download area.

Can anyone enlighten me on how the Ballscrew is held and driven. I just can't make it out, ?
Maybe Pertsa you can post or send the drawings as you have suggested. I would be very grateful.
Chuck, I,m sorry to stomp all over your article,maybe my post can be moved ?
You did a great job of your conversion and thanks again for your help. I think I'm in favour of the Z axis under ballscrew control.
Regards
George

 

[cfellows]

Can anyone enlighten me on how the Ballscrew is held and driven. I just can't make it out, ?
Maybe Pertsa you can post or send the drawings as you have suggested. I would be very grateful.
Chuck, I,m sorry to stomp all over your article,maybe my post can be moved ?
You did a great job of your conversion and thanks again for your help. I think I'm in favour of the Z axis under ballscrew control.
Regards
George

George, there is no problem with other people posting related topics in this thread. More information and questions are always welcome.

First, on the Z-Axis, I too felt that a ball driven Z-Axis would be better and most other folks have the same opinion. However, Using the existing Z-Axis feed was so much simpler to install and, so far, at least, it has worked flawlessly, even in when cutting harder materials like steel. The weight of the spindle assembly is substantial, probably 15 pounds or more, and I've never had a cutter bounce or lift, even with pretty aggressive cuts.

The ball screws I bought from China had no finished ends. I turned the ends down to half inch diameter shoulder with a carbide cutting tool. The ballscrew is hardened, but carbide will cut it with slow feeds. You can also use a toolpost grinder to take it to final fit and finish if necessary... I didn't.

I then made a 17mm round shank to fit inside the existing X and Y table end bearings. Each shank had socket with a grub screw to fasten on to the ends of the ballscrew. The socket end of the shank has a larger outside diameter to accommodate the socket.

If you are attaching the motor directly to the ball screw, you can buy shaft couplers that will connect two different diameters. These usually are 3 pieces with a rubber center so they will tolerate slight misalignment.

Hope this helps and don't hesitate to fire off more questions...

Chuck

 

[Len-Tikular]

Thanks Chuck,
I value your input.
My reason to go to the Ballscrew Z axis is that I have lost major steps with the arrangement like yours. I broke a couple of cutters and that was on aluminium where the axis lost it's place and drove down through the material!!!! My set cut depth was only .25mm at the time and the tool plunged down about 6 - 8mm deep. I'm not sure if my accel values are correct with regard to the tool retracting. That's when I can here the stepper make a zip sound. I don't think my belt is slipping???
Is there anything more that I can tell you to help you help me what is going wrong ???

Regards

George:wall:

 

[cfellows]

Thanks Chuck,
I value your input.
My reason to go to the Ballscrew Z axis is that I have lost major steps with the arrangement like yours. I broke a couple of cutters and that was on aluminium where the axis lost it's place and drove down through the material!!!! My set cut depth was only .25mm at the time and the tool plunged down about 6 - 8mm deep. I'm not sure if my accel values are correct with regard to the tool retracting. That's when I can here the stepper make a zip sound. I don't think my belt is slipping???
Is there anything more that I can tell you to help you help me what is going wrong ???

Regards

George:wall:

A couple of things come to mind, and please pardon me if I'm stating the obvious. Just trying to cover all the bases.

First, of course, would be to check if the downfeed clamp is loosened. I know, it sounds silly, but I frequently tighten my clamp to make the spindle assembly more rigid during level cutting then forget to loosen it when the Z-axis needs to move. :wall:

The second would be the speed setting on the rapid movement of the Z-axis. If you are using Mach3, you can set the maximum rate of speed in the config/motor tuning menu option. I have 425oz in nema 23 steppers with an inductance of 24 milli-henrys so, while they have a lot of low end torque, they won't spin very fast. The gearing on my Z-Axis is such that it takes 48000 steps per inch of travel. It seems to run consistently in both directions without skipping steps at about 15 inches per minute but I have it set to 10 with acceleration set to 1 in per sec per sec. I keep it set really low since Z-Axis speed isn't really important to me.

I don't know how familiar you are with Mach3, but you can hold down the shift key while you press FN and Down Arrow or Up Arrow to do a rapid movement of the Z-Axis. I set my speed by setting the speed at about 50 inches per minute and run the Z-Axis up and down several times using the computer keyboard. If it skips steps, I drop the speed down another 5 in per minute and try again. I repeat this until it moves smoothly without ever skipping. Then I usually drop it down a few steps until I get the best sound from the stepper.

Hope this helps.

Chuck