Let's Talk VFD's

[Tom Bender]

For my TS I went with a TECO VFD and a VFD rated TEFC motor. Not the cheapest option but solid. Good tech support too. After a few years the VFD died, probably lightning. Of course the replacement TECO was a little different but works well.

A motor only provides one level of torque and can stand rpm turndown to about 30% for a proper motor. And cooling is reduced. For a lathe which needs to deliver full torque at high and low speeds for long run times, keeping the motor at or near full rpm is best. And a wide speed range is needed, more than 30%. So mechanical speed reduction is required. Reeves drive or belt changes combined with a VFD is good.

[David Kumm]

If you need a wide speed range with a vfd, consider a vector duty motor. I have a Baldor TENV on my lathe that will deliver constant torque to -0- and can be run over 120 hz. The high end of course loses hp and torque but the motor is much better suited than the 25-75 hz range of a normal inverter duty motor. Having a back gear on a lathe helps a lot as does the reeves drive mentioned above. 3-5 hp Baldor IDNM or Marathon Black Max motors can be found used or NOS as many don't know much about them. I have two NOS Vector duty duty 5 hp motors that new cost in the 1500 range and both were under 400 delivered. Not a bad option. Dave

[Bill Dufour]

David those 5hp motors can I assume you are running them at 3hp or less? That way you get the hp at low rpm where it would be reduced.
Bill D

[ChrisA Edwards]

This might be of interest

[scott lipscomb]

Here is my Oliver 159 with a VFD, Teco FM50, though I think that model has been replaced with another one. It works well.
IMG_3979.jpg

[Malcolm McLeod]

Lots of mentions of torque at low RPM, but keep motor cooling in mind as well.

Typically, I won't run a TEFC motor at less than 25% (15hz). This keeps some minimal air flow for cooling, and is suitable for motors at >80% duty cycle and >80% loading. ETA - Use some common sense here - 25%rpm/80% duty cycle/80% load won't fly if you put it in a 4sqft pumphouse in the Mojave. Keep sufficient air space around any motor :: don't bury it in sawdust and expect immortality.

If you need still lower spindle speeds than offered by 25% motor rpm, then you can either use mechanical reduction to spindle, or add supplementary cooling (i.e. a fan operating at its rated rpm).

[David Kumm]

David those 5hp motors can I assume you are running them at 3hp or less? That way you get the hp at low rpm where it would be reduced.
Bill D

I run with a full sized vfd. The 5 hp motor gives extra hp at the low end but still loses torque and hp at the high end. Without a reeves or a backgear. the motor size for a lathe is often doubled from what was originally offered to compensate for low and high limitations. Dave