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I have a 6 inch grinder rated at 3200rpms is this too fast for buffing?

Will it burn briar?

If so may need to look at making a speed control with a dimmer switch.

In short, yes.

Most of my buffing is done with a 8" wheel at 1250 RPM.

Boom wrote:If so may need to look at making a speed control with a dimmer switch.

Light dimmer switches are not meant for the type of load an electric motor poses. Chances are, you'll likely burn out the dimmer switch before too long.

Secondly, all a dimmer switch does is place resistance (impedance) in the line, reducing the supply to the motor. Slowing the motor speed this way considerably reduces the torque output of the motor. Years ago I tried a router speed controller, which can handle higher current loads than a dimmer, but it still reduced the motor torque way too much.

Other than a pulley system, there really isn't a workaround for variable speed on a single phase motor.

Thanks for the advice on the dimmer. Guess I'll be looking at a multi speed grinder in the near future.

Yeah, those router speed controls pretty much depend on the motor having brushes. Most grinders these days are brushless, and Ohm's law pretty much dictates that they operate at their intended voltage.

But, if you want variable speed, 3-phase motors and VFDs are actually quite inexpensive. People see "3-phase" and freak since they don't know what to do with it. Or look around for a 80-Volt DC motor and controller, they can be also be found very inexpensively.

Then there's always finding a junked treadmill. Those are DC motors, usually 2.5HP and 130 Volts DC. and if you find them intact, you've got your controller right there too. The amazing thing is, most folks toss out treadmills because they're big, bulky, take up space in their house, and they never use them - not because they're broken. These usually have a threaded shaft instead of a standard keyed shaft, but you can find pulleys with no problems if you need something other than what they come with.

If anybody sees inexpensive DC motors and controllers, please post. I'm making a potter's wheel for a friend, may wind up making several. VFD is just a bit too noisy. I found a 3/4hp motor/controller on ebay for $160, we'll see how it works out.

another option for that motor is to use 4" buffs, that will give you about the same surface speed as an 8" on 1750rpm.

and the buffs are cheaper

The speed of the buffer has a large effect on the quality of the finish. I recently obtained a variable speed grinder. Prior to purchasing the grinder i was mounting my buffs in a table saw that spins at 3500. Now I'm able to create a very glossy finish without any worry about the pipe being riped out of my hands.

speed of the motor is irrelevant surface speed of the contact area is what does the work, larger wheels are easier to work with but it can be done quite well with higher speeds and a smaller wheel