Bench Grinder Speed Control That Works - Sort Of

[DMI]

From the world of hydroponics comes the inline fan speed control (ebay item 260869637663).

Like most of us I had spent time trying to come up with a way of controling the speed of a bench grinder with little sucess, I managed to blow one up in the process, and had sort of given up and started using my lathe as polisher. Along comes my daughter and asks if I can find a new control for her ceiling fan.........................

I ended up phoning the seller to explain what I wanted the control to do and she said that it should do the job but reccomended starting on full speed and then going down.

So the control arrived this morning and being the eager beaver it was tested before my second coffee, it works!

The draw back is that as you are varying the wattage you have to use a very light touch at lower speeds or the wheel stops from lack of power.

So a question for electrical guru's if I strip out the internal gubbins of the grinder and directly hook it up to the speed control will it give better results?

[Sasquatch]

Short answer is no. Motors are designed to work at a certain voltage, they are wound with so many windings and built with magnets of a certain strength and the result is that they are happy running at a certain speed and at a certain voltage. Too much voltage and they get hot, too little voltage and strangely enough, they get hot. Being unable to maintain speed at load means that the cooling system is not cooling as fast as the electrical system is heating, usually, and the motor is much more likely to die an early and somewhat smokey death.

[RadDavis]

Delta makes a variable speed bench grinder. I got one at Lowes, but it's designed to be a variable speed motor.



Rad

[wdteipen]

Yeah, you're not likely to have a whole lot of luck trying to get a non-variable speed motor to be variable speed. Woodworkerssupply.com sells a variable lathe conversion kit that includes a 1/2 hp motor for just under $100. All you need to do is rig a mount for it. I know of one guy who's using it to sand/shape with and is pretty happy with it so far.

[Frank]

If I recall correctly from a much earlier post, Kurt and I exhaustively researched the topic of variable speed/constant torque.

There are only two solutions, Variable Speed DC Motor, or 3-phase variable frequency speed control.

I think Kurt rigged up one of those for his knife belt grinder.

Those fan and light dimmer and router speed controllers reduce torque with reduced speed.