VFD low speed torque?

[Arbutus]

I would like to artificially back-gear my EMCO V10-P lathe to allow very low speed operations and to provide more speed control than the headstock gearing allows.

The lowest spindle speed is 60RPM driven by a 1/3HP 115v single phase motor.

The idea is to simply plug the lathe into the VFD and the VFD into the wall. But its probably not that simple. Also, I'm assuming there is a significant loss of torque at low VFD speeds, but how much?
Is this feasible?

Don

 

[garageguy]

The consensus on wiring in a VFD is that there should be no more than one motor, and it should be wired directly to the motor, no switches between the VFD and motor. There are almost always exceptions to the rules depending on the set-up. If you do some looking you will find a ton of info on VFD's and how to use them. Good luck.

 

[Susquatch]

With a good VFD and an appropriate motor you do NOT lose torque at low RPM. You DO lose Horsepower. For a lathe the primary load happens when it comes up to speed. You should be fine doing what you want to do.

However, your fears are correct. You can't just stick a VFD into the power line. Also, VFD's work best with 3 phase motors. So it will take some significant rewiring.

I sincerely believe it is worthy thing to do. In fact, I am in the process of converting my single phase 220V lathe into a 3-phase 220V system now. I already have the motor and the VFD. I am working on the electrical design now. I would not do it it If I didn't think it was worth doing. The minimum speed on my lathe is 70 and I would like 35.

 

[phaxtris]

It's worth the little bit of effort, my lathe is 3ph w/ VFD

There are some benefits other than just speed control, like braking, soft start, etc

 

[PaulL]

What I found is that the VFDs seem to like to ramp voltage along with the frequency, so in a soft-start you're also running at lower voltage. They use a "torque compensation" setting to push more voltage when you're going slowly which for my power hammer allows overcoming the static friction of the pneumatics, but in the long term risks heating your motor more than it should, as the built-in fan can't necessarily handle the heat when running slowly.
This is, of course, described very poorly, usually as a set of poorly labeled diagrams whose mystery numbers are the number of a programmable setting.