Thread: Bench Grinder Conversion

Voidmonster, thank you. I was just trying (unsuccessfully) to point out that you can use a potientiometer, which is basically what a dimmer switch and the Harbor Freight example above are. All a dimmer switch do is restrict, the voltage, not regulate the voltage. So the voltage that we restrict using a dimmer switch produces heat. Which as other forum members have pointed out, will overheat the grinder motor. A variac, or VFD (variable frequency drive) regulates the voltage and does not produce excess heat as a by-product.
Good call from you!

Originally Posted by shikano53

Voidmonster, thank you. I was just trying (unsuccessfully) to point out that you can use a potientiometer, which is basically what a dimmer switch and the Harbor Freight example above are. All a dimmer switch do is restrict, the voltage, not regulate the voltage. So the voltage that we restrict using a dimmer switch produces heat. Which as other forum members have pointed out, will overheat the grinder motor. A variac, or VFD (variable frequency drive) regulates the voltage and does not produce excess heat as a by-product.
Good call from you!

I'm always glad to pass along my mistakes so others don't have to make them!

It didn't burn anything out, it just didn't work well at all.

Interesting thread, I was toying with doing somthing like this but didn't want to burn down my workshop...

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

correct, while there are workarounds such as a variac- would work for speed- with all of these you are suffering loss of power with loss of RPM. What you would do best with is a tri phase, DC perm mag, even an old treadmill motor and controls. So you get constant power under torque- I confess I didn't read what were building, but I saw a grinder and if you need the power of a grinder motor- you need to pick the right motor first for speed control to not limit your power.

Trying to make a buffer or a belt grinder? You can also use belts and wheels, calculate ratio for size to speed and if a single slower speed is what you want- you'll have more torque at lower rpm.

Thanks folks. I'm not trying to thread jack and my apologies to the OP. I'm on a budget and my original thought on reading the thread was to give it a go. After thinking more about it I decided to look for a variable speed machine. I am in the process of reading through the numerous and awesome threads in the workshop section. I read where someone stated, "Do your homework" and then go shopping so you don't waste money." So my quest at the moment is to find a grinder/polisher to work an estate razor through the restoration process.
Any suggestions would be great.
Again, my apologies to the OP. I didn't mean to hijack your thread.
On the bright side. I managed to buy a used drill-press and band saw on Kijiji and saved a couple of hundred bucks in the process.