Converting a 12x36 lathe to 3-phase power.

[Highpower]

I had posted this some time ago at another forum - and was asked if I would post it here as well. It's my run-of-the-mill import 12x36 lathe that I used as it came from the factory for 10 years before converting. I wish now that I had done it much sooner...
-----------------------------------

I just thought I would put up a few pics of my attempt at making a silk purse from a sow's ear.

I bought this lathe (12x36) to be a step up from my little 7x10 mini-lathe. It was nice to be able to work on larger diameter and longer items with the new lathe. But something that I missed compared to the mini-lathe was the restricted number of spindle speeds available to me on the larger lathe. This became a real problem for me when threading to a shoulder because the lowest speed on the lathe was 60 RPM (66 actual). The chuck would free wheel for quite some time after being shut off, and it is not equipped with a spindle brake. I'm afraid I am just not that coordinated to pull off that kind of timing.

So I set about trying to resolve that issue. I purchased a new 2 HP 3-phase motor to replace the factory 1-1/2 HP single phase motor. Bigger is better, right? (LOL) One of the first problems encountered was that the motor shafts were a different size, which meant that the factory drive pulley would not fit the new motor. And of course I could not find a new double pulley in the configuration I needed. But I did find single pulleys of the proper sizes. Time to modify!



After getting the motor mounted it was time to install a VFD to supply the 3-phase power to it. My lathe sits in the middle of the floor so there aren't any near by walls to mount it to. I just attached it to the rear of the factory electrical box and attached some lexan sheets to serve as a shield against getting any swarf/chips inside the VFD. I also added a large braking resistor.



To finish it off I mounted the VFD control unit remotely near the front of the lathe for convenience and also installed a "tachulator" from LMS, which displays spindle RPM and SFM readouts. I made an encoder wheel and mounting block to simplify the installation of the optical sensor on the lathe.



I also added a toggle switch on the right side of the VFD control box, that allows me to switch control of the lathe motor between the VFD panel and the factory control lever on the lathe apron. Flip the switch UP, and I can start/stop the lathe with the VFD push buttons. With the switch DOWN, the normal lathe lever is in control.



After some fine tuning I am now able to run the lathe as slow as 2 (TWO) RPM!
Threading to a shoulder is no longer a problem.