Programming a VFD is a Waste of my Giant Cranium

Today the new old motor for my lathe arrived. It looked like it came from Al Capone’s vault. The paint was in bad shape, and it was beaten up. But when I connected the VFD, it ran. Not smoothly, but it did run.

I had to get down on the garage floor to get the bolts out of the base of the old motor. Then I had to contort myself into the space behind the lathe to get the wiring hacked out of the conduit and boxes. Getting the pulley stack off the old shaft was a joy, believe me. Then I had to persuade the key to come out of the shaft keyway with a hammer and punch. I cleaned the pulleys with the last of my orange-based gun spray, and I put the pulleys on the “new” motor. I guess I’m ready to install it in the lathe. TOMORROW.

The motor I got today is nothing to write home about. People talk about how great old industrial motors are. I have my doubts. This thing makes a sound on every revolution, so my guess is that the bearings are not great, and the shaft looks like someone used it as a johnson bar.

When I put it on the VFD, it made a whistling sound so loud and shrill it was not acceptable. It would drive you crazy to use the lathe with that noise going on. I figured something was loose in the motor, but it turns out the signal to the motor has a pulse frequency, and that’s the problem. Apparently the waveform of each phase is made up of spiky digital pulses at a much higher frequency. I’m guessing here from a picture I saw. Somehow, if you let the pulses get too far apart, it makes your motor whistle. If you let them get too close together, it creates RF interference. On my VFD, you can vary it between 5 KHz and 14 KHz. I decided to ramp it right up to 14. To hell with the radio. Then I felt bad about my neighbors, and I decided to test it. The RF made Todd Schnitt’s show sound bad in the garage, but in my car, twenty feet away, he sounded fine. Who cares about radio interference that disappears after twenty feet? I ran it right back up to 14, and now the whistle is very quiet and sort of pleasant.

I found a really nice Baldor on Ebay for a small fraction of retail. I am considering buying it. The frame is the same. It should work fine. But I want to be sure the VFD won’t kill it. I know I can get an inverter-ready motor, but I’ll have to wait until one becomes available at a price I like. I’m not sure if it’s necessary.

I loves me some Baldor.

A thread on Practical Machinist says failure of a standard motor due to inverter use is nearly unheard-of, so maybe this is the thing to get. I can sell both of the motors the lathe seller gave me. Maybe I’ll get part of my investment back. I’ll say they APPEAR TO HAVE VERY LITTLE USE. That phrase worked on me. Maybe it will work on someone else.

A company called Orion makes add-on fans for motors running on VFDs. Neat.

I guess I haven’t learned my lesson, because I am corresponding with another machinery dealer. And it looks like I can get a Chinese split air conditioner for the same price as an American unit, without cutting giant holes in the wall. I don’t know if it will really cool 600 square feet, but I’d be happy if it even came close. It’s 12000 BTUs. I guess I could sit right next to it and pour ice down my pants.

If the garage gets too swanky, I’m afraid I’ll never leave.

I have been trying to find the best way to mount the VFD, and I think the answer is to get rid of the drum switch completely (using the VFD to reverse the motor), mount a piece of stiff sheet metal to the back of the headstock (over existing bolts) and mount the VFD to the metal. It would be right in my face, ready to use. Beautiful. Oddly, I happen to have a piece of sheet metal that would be perfect. This would be a good excuse to make a template and do some plasma cutting. Or I could make a plywood support instead, which would give me an excuse to run the mighty Powermatic.

This will be sweet. Some day I may even make something.