Lathe CNC Conversion Questions …

[simspace]

I have an Emco Maximat Super 11 lathe. I have already ripped out all the original electronics and converted it to use a VFD.

Now I want to do full-blown CNC conversion! I will most likely go the servo route instead of the stepper route.

The big decision for me is replacing the main headstock motor and ripping out all the drive gears.

There's a few reasons why I want to remove the headstock gears and replace the headstock motor ...

1. The main reason is worn/failing gears or worn/failing gear shifting forks. The gearbox has become really noisy especially in the low gears.
2. I want the CNC system to control all motors.
3. The lathe will be much quieter without the gears (a "nice-to-have" but not important).

What type and size of motor should I use to drive the headstock?

Is there a reason I should not replace the headstock motor?

Is there a reason I should not remove the gears?

I am still learning about the CNC conversion process, so any advice is appreciated.

Thanks!

 

[JimDawson]

A direct drive spindle motor will work fine as long as it has enough torque. You really want a servo motor for that application to get a flat torque curve from 0 to max rated speed.

A 2.2kW should work OK for that small lathe. A 1.3:1 reduction would give you the same speed range you have now, with no gears.

My prefered motor for this application would be

https://www.automationdirect.com/selectors/ls-servo/motoroptions?partno=APM-FE22DMK-AD&230-1phase=true&230-3phase=false&460-3phase=false

 

[simspace]

@JimDawson thanks for the response. Wow, that's pricey! Maybe I'll have to stick with the current motor, gears and VFD and get the other axes and threading working first. I assume there's a way of getting Linux CNC to control the headstock motor speed via the VFD. I'll have to research that. I'll also check eBay for used servo motors and controllers to see what's available.

 

[JimDawson]

@JimDawson thanks for the response. Wow, that's pricey! Maybe I'll have to stick with the current motor, gears and VFD and get the other axes and threading working first. I assume there's a way of getting Linux CNC to control the headstock motor speed via the VFD. I'll have to research that. I'll also check eBay for used servo motors and controllers to see what's available.

Yeah, good CNC hardware can be a bit pricey. I think I paid about $3600 for my lathe servo spindle motor, 7.5kW. It is possible to do almost the same thing with a standard 3 phase motor and a good sensorless vector VFD. You would still need a motor in the 3hp range to power your spindle as a direct drive.

If the LinuxCNC has a 0-10V output available then you should be able to control a VFD with it.

 

[JeffS]

I have an Emco Maximat Super 11 lathe. I have already ripped out all the original electronics and converted it to use a VFD.

Now I want to do full-blown CNC conversion! I will most likely go the servo route instead of the stepper route.

The big decision for me is replacing the main headstock motor and ripping out all the drive gears.

There's a few reasons why I want to remove the headstock gears and replace the headstock motor ...

1. The main reason is worn/failing gears or worn/failing gear shifting forks. The gearbox has become really noisy especially in the low gears.
2. I want the CNC system to control all motors.
3. The lathe will be much quieter without the gears (a "nice-to-have" but not important).

What type and size of motor should I use to drive the headstock?

Is there a reason I should not replace the headstock motor?

Is there a reason I should not remove the gears?

I am still learning about the CNC conversion process, so any advice is appreciated.

Thanks!

I am thinking of doing my own CNC conversion, too. Once I find an appropriate lathe (any suggestions?). However, I have built (from scratch) and re-built a CNC gantry machine. With that said, I would consider driving your lathe spindle with a VFD controlled motor of appropriate size. That way your CNC controller can turn it on/off and control RPM. Typically these days you will find 400Hz motors and VFD's that are very reasonable in price. 400Hz will give you 24,000RPM which would scare the pants off of me on a lathe of any size, so I would consider a mechanical method of reducing that so you can gain a torque advantage without having to buy a truly beefy motor ... and power it. I have a 2.2 kW (3Hp) 400Hz motor and if I reduce that by 12:1 then I can spin my lathe at 2000RPM (plenty) and gain a great deal of torque. Probably enough to do some damage so consider that.

As for using servos, I assume you are contrasting that to stepper motors. Keep in mind that if you use an encoder with a stepper motor and close the loop, you have a servo system - just using a stepper motor rather than a BLDC or brushed AC motor. My gantry machine uses closed-loop steppers and I can machine to .0002" as I built a very rigid, tight tolerance machine. When I upgraded my machine, I went from open-loop steppers (NEMA23) and MACH3 to a MASSO G3 controller with closed-loop NEMA23 3Nm motors that I bought from them. It is quick, quiet, and strong enough to machine anything from wood to aluminum, though I haven't tried steel (and probably won't). I kept my TechnoMotor 400Hz 2.2kW spindle and the Lenze VFD that powers it.

Don't rule out steppers (closed loop) as they are much less expensive. And, decent 400Hz spindles and appropriate VFD's are also very affordable these days. Please keep in mind that while I have built my own machine and done stuff like this for decades, I am not an expert and can always stand to be corrected. If anyone here finds fault with what I have written here, please say so. I want this information to be of as much good use to you as it can be. Best of luck! Cheers.

 

[JimDawson]

I am thinking of doing my own CNC conversion, too. Once I find an appropriate lathe (any suggestions?). However, I have built (from scratch) and re-built a CNC gantry machine. With that said, I would consider driving your lathe spindle with a VFD controlled motor of appropriate size. That way your CNC controller can turn it on/off and control RPM. Typically these days you will find 400Hz motors and VFD's that are very reasonable in price. 400Hz will give you 24,000RPM which would scare the pants off of me on a lathe of any size, so I would consider a mechanical method of reducing that so you can gain a torque advantage without having to buy a truly beefy motor ... and power it. I have a 2.2 kW (3Hp) 400Hz motor and if I reduce that by 12:1 then I can spin my lathe at 2000RPM (plenty) and gain a great deal of torque. Probably enough to do some damage so consider that.

The only problem with using a 400Hz motor is it really does not like to run any slower than about 18K RPM. Below that it will start over heating. I suspect this has to do with air flow as much as is does with the winding design. That would not be my choice for a lathe spindle motor, it would however work great for a router spindle.