Thoro:
My mill had a motor with a metric D90 frame (flange mounted), but the shaft was 19mm diameter, not the normal 24mm of a D90 frame. Look at a Leeson 192206 (try
http://www.electricmotorwholesale.com). 19mm is the diameter of the shaft on a D80 frame. I could not find any off-the-shelf metric motor to drop in without needing to machine down the shaft to fit into the top gear. I think that the mill's manufacturer (Sabre is the label) originally used a 1.5HP D80 frame motor, then upped it to 2hp and for them it was easier to order a D90 motor with the smaller shaft than to change their gearbox. Incidentally, the flange mounting is the same for both sizes. If your motor fits the D90 outline, including the shaft size, the 2HP Leeson should drop right in. The link above has an outline drawing under the "files" tab.
I did suggest that the stress on the starter switch would be less at the lower voltage, but general wisdom says to operate the motor at the highest voltage available for other reasons, such as lower IR drop in the wiring. If you look at the nameplate on your motor, it will list available voltages. On mine, it listed 230/460, so it was already operating at the lowest voltage. I just think the contact design on my motor was inadequate.
If the Leeson fits and you are up to the rewiring job, it would result in a better mill. In addition to the advantages of variable speed, I think the Leeson is a better motor than what comes on most of these RF-45 clone mills. I can't emphasize enough how getting the two contactors, capacitors and centrifugal switch out of the electrics improves the durability.
I have attached the wiring diagram I created for my mill. (I am an electrical engineer and while motors and such were not my specialty I consider myself competent to do this design.) Notice, no contactors are needed. Additional information:
1. Fuses are required by the VFD. They are of a specific type, listed in the VFD manual.
2. I added a fan for optimal cooling of the VFD.
3. My front panel switches are a POWER switch, FWD-STOP-REV, and E-STOP.
4. Only the POWER switch needs to handle 240V @20A, the others are switching 24VDC from the TECO that it uses for logic inputs. How they control the unit is part of the software setup.
5. Do NOT put any switch or relay between the VFD and the motor. The VFD can actually stop the motor quicker than disconnecting it which might damage the electronics. I think my ramp-down speed is set to 0.8 seconds for E-STOP.
I have no doubt the cheapest solution for you is to manicure the motor's centrifugal switch contacts and replace the starting cap if it is shorted. A new motor and VFD will cost you about $400, depending on how much you have to spend for the electrical bits and pieces. If your mill is under warranty maybe you can get the mfr. to replace the motor? But if you do the 3 phase upgrade, it will be a lot more durable plus have variable speed at the twist of a knob. Let me know if you need any additional info.
Craig
