Servo for CNC conversion of 8x30 knee mill

[slow-poke]

This is for hobby use not professional.

I have two manual mills, I converted one of them to CNC about 10 years ago using NEMA34 steppers and using Mach3 to control. I made a custom control panel it all works quite well and I'm quite happy with it. Only complaint is maximum speed, I'm using the original ACME lead-screws. This discussion is not about that conversion, only to give readers some idea of where I'm at with CNC type stuff.

I now want to convert my new (old 1989) 8 x 30 knee mill, I'm considering using ballscrews and servo motors this time. Not sure if I will use Mach3 again or something else, that's another discussion but do like the idea of using servo's with simple step and direction signals for drive.

I know someone that has converted a similar knee mill and he used Clearpath SDSK 3421S-RLS servos (NEMA 34, 289oz-in continuous, 1100oz-in peak) directly driving the screws and he is quite happy with the performance. That servo sounds perfect specification wise, but are expensive for my hobby type requirements.

I have read that there are now more affordable (Ali-Express etc) servos, would appreciate any information/suggestions for these lower cost servos and suitable drivers that incorporate the feedback from the encoder.

Images (everyone likes pictures). Green is old, white is new.

 

[koenbro]

There will be many different directions the opinions will take you. Most of us have experience with one combination, made it work, and now swear by it. You get the idea.

Here is my advice: If you call Automation Direct, they might suggest a good product or package. I would stay away from Ali Express servos: uncertain quality, limited customer service, no documentation. Better to save up some money and do the last setup first rather than being penny wise, pound foolish, and all that. That is my bias and I acknowledge it.

My own setup is with Clearpath + Acorn on the mill, and chinesium steppers + Mach4 on the Avid plasma table. The steppers were purchased from Avid though, and they configured the electronics, so everything meshed together without problems. No way I would have cobbled it together though. OTOH with the mill, I put it all together without any prior experience. Had to call Technics once, and service was flawless. I can recommend them VERY HIGHLY.

 

[strantor]

You can get cheap AC servos from DMM (better prices on their eBay store) but I can't recommend them as they gave me nothing but trouble. Granted I was using them for something other than the typical step/dir CNC application. I was trying to use them in speed mode with an analog voltage signal, which is an operating mode they are supposed to support, but everything was very buggy and kludgey. Hopefully they have the step/dir game down pat, and wouldn't give you any grief.

I bring them up to point out that they are the closest thing to "hobbyist budget" AC servos you're likely to find from any company on this continent and they leave vast room for improvement. I haven't bought any alibaba or ebay ghuanzhou China servos but if I did, I wouldn't expect anything better than DMM.

I don't recommend going that route. Go with name brand servos or stick with steppers. Closed loop steppers are a thing these days, which basically makes them servos, but if you've just really got your heart set on honest-to-goodness AC servos (and I understand if you do, they are the undisputed champ after all) then my recommendation would be to look at used name brand stuff. Specifically I would suggest looking at Allen Bradley Kinetix and Ultra 3000 servo drives on ebay. The ultra 3000s are pretty easy to set up as servo drives go, especially if you're using a motor that isn't the exact MFG part # that the drive was born to mate with.

 

[Unlogic]

I'm doing a CNC conversion of my Optimum MH50V mill at the moment and I opted for Delta B3 servos.

They may be a bit overkill for many machines but they offer industrial quality and comprehensive documentation at very reasonable prices.