Any reason I can't do this?

[Jim Tobias]

I have one of these (below) and have added a pneumatic sanding drum. I would like to slow it down on occasion. Is there any reason that I can't get an "after market" speed control and add it to this? If so, any suggestions as to where I might find a good variable speed switch?

Thanks,
Jim
192817

[Chris Mahmood]

You can only vary the speed of an induction motor by changing the frequency of the power, not the voltage like on a universal motor. A VFD (http://en.wikipedia.org/wiki/Variable-frequency_drive) would work but so would a step pulley on the left-hand shaft and a spare motor.

[Rod Sheridan]

Hi Jim, as Chris indicated, you'll need a VFD to change the speed of an induction motor.

Unfortunately you cannot lower the speed of a standard single phase induction motor below aproximately 80% or the starting switch will close, engaging the start winding.

A three phase grinder would be ideal, or you could buy one of the variable speed grinders (I have a Steel City grinder) which uses a pulse width controller to slow the grinder. This grinder motor however is built for the task and has a continuous duty run winding.

Regards, Rod.

[Dan Hintz]

Is everyone sure this is an induction motor? If it's a typical brush type, a router speed controller would do what you need.

[John McClanahan]

My guess is the start capacitor in located in the base.

John

[Rod Sheridan]

It may not have a start capacitor since it doesn't need much starting torque. I have a grinder with a split phase motor, no start capacitor..........Rod.

[Steve Ryan]

Is everyone sure this is an induction motor? If it's a typical brush type, a router speed controller would do what you need.
If it were a universal AC-DC brush type motor it would likely turn very high RPMs. High enough to make grinding wheels explode. Does not look to have a gear drive.

[george wilson]

Your motor needs to be 3 phase to use a variable frequency controller. That probably is a capacitor start motor.

[Rick Lizek]

As stated you can't slow it down. You could put a smaller diameter polishing wheel on it and it will change the rim speed so it will seem slower. Why do you need to slow it down anyway?

[Jim Tobias]

Rick Lizek
As stated you can't slow it down. You could put a smaller diameter polishing wheel on it and it will change the rim speed so it will seem slower. Why do you need to slow it down anyway? I am using a pneumatic sanding drum and when doing curved work I woul dlike to slow it down for more control of the sanding.
Sounds like I can't slow it down so I may need to look at other solutions for this part of the sanding process.
Jim

[Rick Lizek]

When I first started woodworking in a small factory in the early 70's we used "balloon" sanders a lot including sanding the corners on pine bench seats 2" x 16" X 72" and we did it by moving the bench seat against the sander. I would say the solution is more practice, not slowing the sander down. Is your grit too aggressive and causing the problem? Adjusting the air pressure in the bladder is a big help, finer grits and the rotation all are factors. Working under the drum gives more control than working over the drum. So the rotation of the sanding drum should be downward as you face it. It makes a huge different in control of your sanding. I would never want to slow the speed down.

I think folks often overlook the real solution over the perceived solution. Often the question people ask isn't really the problem that folks are trying to solve.

[kevin loftus]

I use my drill press for sanding curves Jim. :)
I just change the belt around for different
speeds. :)