New spindle motor - Servo or Induction?

[Jim Dawson]

OK Please don't shoot me but I'm new to this topic but I would also like to remove my large 3-phase 2HP motor on my Tree Journeyman 200R machine and replace it with another servo motor or something where I could do rigid tapping and other fun things. My spindle currently runs at 3300 when in high gear so I was thinking I could remove the transmission and large old motor and just replace it with a nice new servo motor like this: https://www.teknic.com/model-info/CPM-MCVC-3426D-RLN/ and just drive the spindle directly from that 1:1 coupling. This servo will run at 5300 RPM which is nearly 2x the speed my existing system will do so that would be great but it would (should?) also give me the low end I need to do rigid tapping and similar things. -Am I crazy or am I on the right track? Please offer feedback with the understanding that this is my first go-around with even thinking of doing this. I would buy a 75v power supply to drive the motor and then just control it with LinuxCNC ...that's my plan as of right now in the infancy stage of development!

I think you would be very disappointed with the performance of that motor for your application. Your current motor develops about 8Nm base torque, the base torque of the motor in the link is 0.5 Nm torque. Basically you would be replacing a 2 HP motor with a 1/4 HP motor. You would do much better with this one, but the RPM is limited. https://www.teknic.com/model-info/CP...1003A-RLN_Fan/ Neither of those motors would be my choice for a spindle.

This motor might be worth a look https://store.dmm-tech.com/products/...ac-servo-motor

[hatch789]

I think you would be very disappointed with the performance of that motor for your application. Your current motor develops about 8Nm base torque, the base torque of the motor in the link is 0.5 Nm torque. Basically you would be replacing a 2 HP motor with a 1/4 HP motor. You would do much better with this one, but the RPM is limited. https://www.teknic.com/model-info/CP...1003A-RLN_Fan/ Neither of those motors would be my choice for a spindle.

This motor might be worth a look https://store.dmm-tech.com/products/...ac-servo-motor

Thank you Jim, I'm just trying to learn how this all works as I have had so many other things I was fixing, replacing and repairing on the Mill that I never gave my spindle motor any thought before this year. Now that I have a lot of other things in hand I would like to consider this as a potential project. So from what you wrote we can't look at peak torque really, we have to just look at continuous torque numbers and in that case I understand what you're saying. How do big machines like HAAS VF series (and many of the newer machines out there today) run their spindle? Are they using something different than servo motors? I'm just trying to learn.

The other thing I'm trying to do is possibly get rid of the need for my rotary 3-phase converter. Right now I use it because this mill has a 3-ph 2HP motor driving the spindle but if I replaced that motor I could easily re-wire the machine to run off of my 220v single phase at home. That would be pretty cool. I just don't want to cripple the machine in the process. So that's why I want to make sure I do good research here first if you guys are willing to help me out with my knowledge gap.

[Jim Dawson]

Thank you Jim, I'm just trying to learn how this all works as I have had so many other things I was fixing, replacing and repairing on the Mill that I never gave my spindle motor any thought before this year. Now that I have a lot of other things in hand I would like to consider this as a potential project. So from what you wrote we can't look at peak torque really, we have to just look at continuous torque numbers and in that case I understand what you're saying.

Peak torque is just that and the motor won't run for long in that range. Peak torque on your 2 HP motor is in the 20 Nm range. My 3 HP on my knee mill pretty much runs out of torque when tapping 1/2-13 in steel, the load goes to about 150%. It is geared up 1.5:1 for higher spindle speed. I have a sensorless vector VFD on it so it will produce full torque at near zero RPM

How do big machines like HAAS VF series (and many of the newer machines out there today) run their spindle? Are they using something different than servo motors? I'm just trying to learn.

I have a Haas and as near as I can tell, the Haas will only index to what I am guessing is the spindle encoder index pulse. I think spindle drive is kind of a hybrid VFD/Servo drive. But as near as I can tell they use a standard(ish) induction motor for the spindle motor. Probably use a lot of DC injection when indexing. I have tried this trick on my lathe, but haven't had a good result.

I do rigid tapping on my lathe all the time, running a tapping job on it right now. It has a standard(ish) 3 phase spindle motor and a sensorless vector VFD drive. This is done by electronically gearing the Z axis to the spindle encoder. Your software would need the capability of electronic gearing, not sure if LinuxCNC will do that or not.

The other thing I'm trying to do is possibly get rid of the need for my rotary 3-phase converter. Right now I use it because this mill has a 3-ph 2HP motor driving the spindle but if I replaced that motor I could easily re-wire the machine to run off of my 220v single phase at home. That would be pretty cool. I just don't want to cripple the machine in the process. So that's why I want to make sure I do good research here first if you guys are willing to help me out with my knowledge gap.

You could do as I indicated above and install a sensorless vector VFD and run it on single phase, or keep the RPC and run the VFD on 3 phase.. The VFD will give you a nice speed range and full torque at low speed.

[spumco]

The VFD will give you a nice speed range and full torque at low speed.

This. In capital letters.

I started the thread and search primarily because I was looking for something that could provide higher spindle speeds and lower weight, without trading off torque. Weight and physical size are the problem in my case. And a permanent magnet AC servo of the same basic power/torque/speed range is significantly lighter than an induction motor. The AC servo does away with the problems I've experienced with BLDC motors (RPM hunting, oddly low torque).

What it boils down to -- more or less - is volts & amps. I only have so much of either to play with, and nothing I can do is going to get me a magic spindle motor. So I opted to get the most powerful servo I could find that was below my single-phase 240vac amperage budget, and one with a rated speed well below the max spindle speed. Thinking is that I wouldn't need as much torque with a small cutter at 8kRPM as I would a 1/2-13 tap down low.

In the case of Hatch789, a VFD is the perfect solution. You can get a single-phase VFD for that 2HP induction motor and you'll get much better performance. Assuming your spindle & gears are up to it you can probably double the top speed to 6600RPM. You might want to run some speed/feed numbers with typical cutters and material - your Tree may not have the feed rate to keep up with that RPM. In that case the motor will not be the limiting factor.

In addition, you can fit an encoder to the spindle with a timing belt and if your control is capable of it that is enough to do rigid tapping. No servo needed. If your control doesn't permit spindle encoder inputs, then no servo is going to help...

A Hitachi WJ200 or Automation Direct GS-2/3 VFD are both quite inexpensive VFD's suitable for driving a 3p induction motor from 1p. There are plenty of other brands, but i have had good experience with those two.