Re: New spindle motor - Servo or Induction?
Originally Posted by
hatch789
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.
Jim Dawson
Sandy, Oregon, USA