CNC Mill Conversion Questions.

[Eddyde]

Hi All,
I am planning to convert a Milling Machine to CNC. so far, I have read a couple of books on the subject and done a lot of internet research. I am leaning towards a new bench type, SIEG or Rong Fu type mill since getting a Bridgeport into the basement seems a bit too daunting. However, I do love vintage machines and might go that route if the right machine comes along.

I have a couple of questions and would appreciate any help:

1. Has anyone used the ball-screws, stepper/servo motors, etc. from China? The pricing is very attractive, I know the big name gear is better but is it really worth the exponential investment?

2. Can I use the linear encoders from a DRO in place of the rotary encoders on servo motors? It seems such an arrangement would compensate for any backlash in the system and be more accurate. I know some of the very high end industrial machines use this method but I don't see much info on DIY versions.

Many Thanks

Eddy

 

[Karl_T]

...

2. Can I use the linear encoders from a DRO in place of the rotary encoders on servo motors? It seems such an arrangement would compensate for any backlash in the system and be more accurate. I know some of the very high end industrial machines use this method but I don't see much info on DIY versions.

Many Thanks

Eddy

Maybe, some of them are compatible. heidenhine (SP???) for sure works. They need to put out a quadrature encoder signal. IMHO, this is for high end machines - you need a really tight machine or the servo will hunt all over and not be stable.

Just my 2 cents, if you're going with Asian equipment, stay with steppers and go Mach control. Low cost, makes a fair hobby machine.

If you want something faster and more rigid, do what it takes to find a CNC machine with a dead control. They are out there, may have to travel. Bridgeport series I and II, Excello, Shizouka, Heidenhein (SP???) Wells, Supermax are just a few names. Then go with DC servos and LinuxCNC for a control with position feedback.

I'll just mention Camsoft is higher end yet. I own and have installed many of these systems.

Karl

 

[JimDawson]

Hi All,
I am planning to convert a Milling Machine to CNC. so far, I have read a couple of books on the subject and done a lot of internet research. I am leaning towards a new bench type, SIEG or Rong Fu type mill since getting a Bridgeport into the basement seems a bit too daunting. However, I do love vintage machines and might go that route if the right machine comes along.

I have a couple of questions and would appreciate any help:

1. Has anyone used the ball-screws, stepper/servo motors, etc. from China? The pricing is very attractive, I know the big name gear is better but is it really worth the exponential investment?

2. Can I use the linear encoders from a DRO in place of the rotary encoders on servo motors? It seems such an arrangement would compensate for any backlash in the system and be more accurate. I know some of the very high end industrial machines use this method but I don't see much info on DIY versions.

Many Thanks

Eddy

I'm not sure about the hardware from China, the servo systems seem to be kind of new on the market so there is not much history yet, I have not heard anything good or bad. The stepper motors are a pretty mature product and I have heard no complaints. The stepper drivers do lack some of the features of some of the better American hardware. Ball screws?, probably OK, but who knows.

There is no reason that you could not use linear scales in place of the encoder, as long as the controller will accept the output from the scale. If the scale outputs a standard quadrature output, then you should be good to go. It depends on what motion controller you choose to use. You are correct, doing it this way compensates for any backlash and any leadscrew error. I use 1 micron magnetic scales on my machine.

Depending on what stepper drive/motion control system you decide to use, it is possible to close the loop on the stepper system and also operate the stepper just like a servo in velocity mode, rather than step & direction.

 

[JimDawson]

Maybe, some of them are compatible. heidenhine (SP???) for sure works. They need to put out a quadrature encoder signal. IMHO, this is for high end machines - you need a really tight machine or the servo will hunt all over and not be stable.
Karl

I know that Anilam Crusader M controllers will take a 10 micron quadrature input also, not sure about any others.

As long as it is possible to adjust the PID loop parameters, you should be able to tune the system so it doesn't hunt. If you can't get to those parameters, then I would say it would be almost impossible to tune and would be unstable. My machine holds +/- 1 count (0.000039 inches)

 

[chuckorlando]

Jim if you lived close by, you would have to beat me out your shop with a broom. I need a good couple days with a guy like you to wrap my brain around all this. It's like reading spanish to me, and I cant read spanish ahaha

 

[JimDawson]

I don't read Spanish either, but I do a pretty good job translating "Chinglish" from the user manuals.:lmao:

 

[Karl_T]

I'll point out a real economical way to do linear encoders:
http://www.usdigital.com/products/encoders/incremental/linear/LIN

My motion controller (Galilmc.com) allows PID tuning with one encoder and destination control with a second. Put the linear unit as destination control. This would be the best of both worlds. Bet there are others out there with this feature.

Karl

 

[JimDawson]

I'll point out a real economical way to do linear encoders:
http://www.usdigital.com/products/encoders/incremental/linear/LIN

My motion controller (Galilmc.com) allows PID tuning with one encoder and destination control with a second. Put the linear unit as destination control. This would be the best of both worlds. Bet there are others out there with this feature.

Karl

I use Galil products also. You are correct, there are others that have the same features, but they cost a lot more than Galil, and are much more difficult to setup and program, and in most cases you have to buy their proprietary software to program them. I do a lot of my Galil programming in Notepad or Excel.

 

[Eddyde]

Thanks for the link and the info, very helpful.

 

[Gary Ayres]

Good luck with the conversion.

I plan to do the same to my 626 mill next year, so will check in on this thread from time to time.