Thread: Bench Grinder Conversion

There was a discussion about this on "another website" recently. I think it boils down to if the motor is the wrong type (which most buffer motors are) it wont go more slowly, but you'll lose all your torque, so very little pressure on the wheel will slow and stop it. If you still have plenty of torque with the motor slowed you should be ok.

Went and double checked it. If its a brushless or synchronous motor it shouldn't work, at least not with a normal rheostat that just reduces power. I have no idea if that light dimmer switch is different somehow, though.

Ok so I've been using this for a little over a week now and it works well. It's not perfect, I have to start it a full rpm and then turn it down. I can only turn it down to about 60% speed because any lower and you tend to lose torque. I'm having no issues with the switch warming up ( I didn't really think I would it's a 600 watt switch) the motor is not getting warm either. I do stall it out when loading up the greaseless compound, but I think I would do that with any of these small 6" bench grinders that are only 3.4 amp.
So my conclusion is that it works and it's a cheap way of doing it. And always you get what you pay for.
$35 grinder
$3 switch
$2 out let
$2 box
Cord I had (burnt out the one end plugging in my diesel van)

Any update available or would else like to comment on the safety/effectiveness of this solution?

I just picked up a 6" 3600 rpm Ryobi (Chinese import) bench grinder and I'm considering trying this method this to slow it down.

Í wouldn't know about the motor, or different types of motor, though putting your hand on it and seeing whether it get hotter than it used to might (just might) give you an early warning. The Prime Minister asked Michael Faraday just what this new electricity of his was, and Faraday answered "I don't know, sir, but I'd wager you'll tax it." Who am I to claim to know better?

I'm rather surer, however, that overloading any switch is not a good idea. The grinder is probably safer than most things though, since you would have no reason to leave it running and unattended.

I picked up a 6" variable speed Porter Cable bench grinder for $70 at Lowes. Haven't had any issues with it, Just need to take the guards off and away we go.

Originally Posted by whavens

I picked up a 6" variable speed Porter Cable bench grinder for $70 at Lowes. Haven't had any issues with it, Just need to take the guards off and away we go.

What's the lowest RPM rating on that machine?

Research leads me to believe that something under 1800 would be relatively safer for use with blades.

Interesting thread. Here is a picture of a Maximum variable speed grinder from Canadian Tire that retails for $139.00
If you look at the variable speed control to the right of the on/off switch, it sure looks like a dimmer switch to me.

Originally Posted by TrilliumLT

Ok so I've been using this for a little over a week now and it works well. It's not perfect, I have to start it a full rpm and then turn it down. I can only turn it down to about 60% speed because any lower and you tend to lose torque. I'm having no issues with the switch warming up ( I didn't really think I would it's a 600 watt switch) the motor is not getting warm either. I do stall it out when loading up the greaseless compound, but I think I would do that with any of these small 6" bench grinders that are only 3.4 amp.
So my conclusion is that it works and it's a cheap way of doing it. And always you get what you pay for.
$35 grinder
$3 switch
$2 out let
$2 box
Cord I had (burnt out the one end plugging in my diesel van)

TrilliumLT, I think this is a darn fine idea! I don't know why I didn't think of this. Thirty-eight years of being a licensed, Amateur Radio operator and building countless electrical circuits including power supplies and amplifier stages and components in the last 4 decades. I should have tumbled to this earlier. There are several 6" grinders for sale here in my neck of the woods around the $40.00 mark.
I'm gonna scoop your idea and put it to work.

Harbor Freight makes a variable speed controller for a router tool. However that being said; A dimmer switch, potientiometers, router type speed controls only work with universal, brush type motors. A grinder, if memory serves, use an induction motor.
So, yes these will work; but at your or my risk.

The best is a variable frequency drive but by then you might as well just purchase the variable speed grinder/polisher.

https://www.youtube.com/watch?v=-6E1uI8yOy0

Originally Posted by shikano53

Harbor Freight makes a variable speed controller for a router tool. However that being said; A dimmer switch, potientiometers, router type speed controls only work with universal, brush type motors. A grinder, if memory serves, use an induction motor.
So, yes these will work; but at your or my risk.

The best is a variable frequency drive but by then you might as well just purchase the variable speed grinder/polisher.

https://www.youtube.com/watch?v=-6E1uI8yOy0

The HF bench grinder and buffer are both induction motors and the variable speed control for routers does not work with them.

I've tried it. Save yourself the trouble, it's not worth the experiment.