Need Help!- K. Martin Lathe and VFD?

[jho5820705]

I have a K. Martin Lathe with a bad starter. I would just replace the starter but find that it is no longer available. For the price of a new starter I could buy a 5 HP VFD and use that to control the motor. Is this a viable option or would a VFD not work well with a lathe? If it will work, what should I look for when purchasing the VFD? I have looked at a lot of information here ant at the manufactures sites but am not sure I understand anything at this point. Any help would be appreciated.

[Al_The_Man]

For VFD use, the motor needs to be 220-240 three phase.
What HP size is the motor? Normally the VFD is derated if running it off of 240v 1 phase, and the top end is usually 5hp VFD by many manufactureres.
If by starter you mean contactor, there are many on ebay that run a lot cheaper, make does not matter as long as the specs cover the motor.
Al.

[jho5820705]

The lathe has a 5 hp 3 phase motor on it. The starter relays are made by Allen Bradley and will not stay engaged. When I called the local dealer he said they do not make replacements for those relays any longer and I would have to replace everything for the line in to the motor.

[Al_The_Man]

Originally Posted by jho5820705 I would have to replace everything for the line in to the motor.

Sounds like he was spinning you a line!
I assume it is a reverser? Probably the old style AB Nema frame, the latest DIN style are about 1/3rd the size.
Or is it a push button starter unit?
Normally you would just replace the contactor or reverser and the over load unit.
Unless there is some other reason that is the only thing you should have to replace.
There are other suppliers, such as Square D etc.
Whether it is PB or coil energized it should be a simple task to sub/replace.
If you go with a VFD, you should still provide a disconnect by contactor in the 3 phase input side, this is normally picked up by the E-stop release.
How is the speed changed on the existing motor? For a VFD, you may want to use one other reduction for low rpm work and well as a 1:1
Al.

[jho5820705]

This is an early 1980 vintage German lathe. The motor is a single speed motor. Spindle speed is changed by changing gears. Lowest speed is 34 rpm and highest speed is 1200 rpm. Spindle and motor are started with a lever which activates a relay to start the motor, either forward or reverse. Right now all the starter relays do is chatter and will not engage. I was running it on 3 phase power from a rotary phase converter that I use for the mill. The idea of variable speed is attractive and if I have to change out the starter relays and rewire it a VFD looks attractive, if it will work.

[Al_The_Man]

What is the rated rpm of the motor?
Al.

[jho5820705]

1750 rpm I think. The data plate on the motor is difficult to read without taking the motor out of the lathe.

[Al_The_Man]

That is a 4 pole motor so you can probably run it up to twice that rpm if needed using a max frequency of 120hz with a VFD.
Al.