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4K views 16 replies 11 participants last post by  oldnovice 
#1 · (Edited by Moderator)
I've spent about 2 hours Googling and all I'm getting is a headache plus more and more confused :-(

I'm trying to build a 12" shop made disc sander, and the first motor I tried was WAY underpowered. I dug around in my shop and came up with 2 more electric motors, both of which are plenty powerful, but both of them run at 3450rpm, which is too fast for a sander. Both of these motors have capacitors on them (if that info is helpful)

Since I'm no electricial geenious, I'm looking for some help here. I'll post good clear photos of both the info-plates and I'm hoping SOMEONE way smarter them me can decifer if I can use a HF router speed control to drop the speed by about 1/2… Thanks in advance.

This Doerr motor was from an old air compressor. It has a mounting plate on the base already and the capacitors are mounted on the outer shell of the motor.
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And this Marathon Electric motor came out of a commercial floor sander. It's a beast, and I know it would have enough power. I also already know it is set for 110v. There's no mounting plate on this one but I already have a way to mount it if it'll work.
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The square box on the bottom in this pic is where the capacitors are. That smaller motor in this last pic is the one I tried that is way underpowered for this application.
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#5 · (Edited by Moderator)
A VFD (variable frequency drive) is the only effective electronic method that will control the speed of an induction motor. That is not the type controller often referred to as a router speed control.

I say effective electronic method because you can vary the speed by a big rheostat or a variable auto transformer but both these methods just reduce the voltage and you lose power faster than you lose speed. Also, with reduced voltage you stand a good chance of overloading and frying a motor.

A VFD will solve your motor speed problem however. It can be set to feed 30 hertz power to a 3450 rpm motor and make it a 1725 rpm motor. The only real shortcoming of these controllers is they cost more than the motor.

By the way, you will need at least a 1 hp motor to run that 12" disk. That's why I just bought the 12" disk sander at HF. It was cheaper than I could buy the motor alone. Never regretted this purchase.
 
#6 ·
Joe, It is too bad Tesla's AC system won. If we used Edison's DC motors, it would be easier to control the speed ;-)

It has been pretty well summed up, no cheap, easy way to control the speed on these motors.
 
#11 ·
Topamax… not sure what the optimum speed is for sanding. I just know that most "standard" 110volt electric motors run at 1725. And I remember reading somewhere that 3450 was too fast for sanding cuz it'll shred the paper
 
#14 ·
Bonda… I'm not actually looking for variable speed. I was just looking to slow it down and I thought maybe the router speed controller (set at low) might do it.

Yes I could use pulleys, but then I'd have to buy the parts to make the disc a separate "stand alone" piece on a shaft with pilllow blocks and run by the motor via pulley system. WHat I have now is the disc is mounted directly to the motor shaft and I was trying to use that setup.
 
#17 ·
As stated above, those are both induction motors and cannot be speed controlled by a router speed controller.

A VFD drive will work if you can find the correct one for those motors and, it won't be cheap.
 
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