Bridgeport J head 1hp motor replacement
Iím looking for a motor to replace the motor on my 1964 bridgeport J head.
The original motor suffered a tragedy this winter. On a pretty cold day, about 15 degrees, I needed to do some work for a project, so as I fired up the mill Iím looking at the work getting ready to start making chips and I think Ďthe spindle sure isnít spinning up very fastí. Then I looked up at the motor and saw the magic smoke pouring out. I shut Ďer down, but it was too late already. I was running it on a rotary phase converter, which was happy to dump all the current it could (I havenít taken apart the RPC to see if it also smoked). Iíve since built insulated walls & ceiling around the machine tool area and installed a heater to keep them at least 45 degrees (always too late with the improvementsÖ)
The motor is 230/460 3 phase 1hp, with 2.1" long x 3/4" diameter shaft. The J head is the step pulley type. The current power setup is 240V single phase driving the RPC which runs the spindle motor, but after the smoke I bought a 1hp VFD to drive the new motor to hopefully prevent future sadness.
So now Iím looking at replacement options. I took the motor to a local shop, they said $700 to rewind. Iíve seen kits with adapter plate and motor on fleaBay for around $750. The motor shop guy stocks a 1hp 3phase 56C with a 1 3/4" x 5/8Ē shaft for $184. I got to looking at the available styles in 1hp 3 phase and found a 143TC that has a 7/8Ē x 2 1/4" shaft, considerably closer to the original. The current motor is 3/4" shaft that sticks past the mounting Ďearsí by about 2 5/8Ē. In looking at the motor step pulley it looks like it was sleeved from 7/8Ē down to 3/4", even if it isnít I can chuck it up in the lathe and bore it out, tho the keyway will be some work. The current motor has some of the motor housing sticking about 1/2" past the surface of the mounting ears down into the pulley area.
Iím thinking my best option right now is to replace the old motor and make the adapter plate to connect the 143TC motor. To get closer to the same amount of shaft into the pulley Iíll need to make the adapter plate recess the motor by a bit. Iíve got some 3/8Ē plate laying around, so Iíll use the plasma cutter to cut a circle about 1/8Ē more radius than the size of the motor, then drop that circle down 3/8Ē and weld it back onto the remaining plate with the mounting ears. That should put my new motor face close enough to the old to work.
With no mill getting the bolt circle for the motor mount and the flange holes is going to be more challenging. Iíve got an old 3/4 hp 120V motor with a step pulley on it that I was thinking I might do a quick hack job to mount onto the mill, just so I can get power to build the proper replacement plate.
Any suggestions or comments would be appreciated.