Thread: Bench Grinder Conversion

Hey guys i thought i would share with you my way of turning my standard bench grinder into a variable speed Bench grinder. Things your going to need are.: 1 A Decent Dimmer switch, 2 A Outlet to pug into, 3 A double outlet box to keep it all in and safe, 3 A Old 3prong extention cord.
Ive now mounted this to my wood Bench Grinder stand. Over time you will more than likely have to replace the Dimmer switch (Because it wasn't Meant to take that kinda load). With this your 3500rpm can be turned down to a 1500rpm Grinder with ease. And saves you the cash of paying for one of the over priced Variable Bench Grinders.

Here is a pick of it

I've always been under the impression that doing something like that on a load bearing motor would burn it out. Let us know how, and how long, it works!

Originally Posted by Utopian

I've always been under the impression that doing something like that on a load bearing motor would burn it out. Let us know how, and how long, it works!

This is the same way a variable bench grinder works. The only thing that's going to get damaged is the dimmer switch over time. I thought the same thing but I ran it by the motor shop I use.

Originally Posted by Utopian

I've always been under the impression that doing something like that on a load bearing motor would burn it out. Let us know how, and how long, it works!

I had heard the same thing, but I am no electrical engineer, and don't really understand what's involved.

I am curious to know how it works out.

If the grinder motor is a universal motor, it can be controlled by a triac circuit. What device commonly uses a triac circuit ? A light dimmer !!!

A lot of the import grinders do not use universal motors so the dimmer thing will burn out the motor. Think about it like this. If this was really no harm on the motor or not a fire hazard to the switch. Why do even the discount lathe, sander and drill press makers use DC variable speed motors? Why not just slap on their regular motor and a $4.50 dimmer switch. Makes you think huh?

Trillium,

Keep us posted. I for one am interested in your findings. I'm hoping to assemble a bit of a rig at the cottage this summer, and I'd love to avoid spending oodles of cash on a variable speed!

I have a variable speed grinder I picked up in Lowes on sale a while ago. It wasn't that expensive, 50.00, maybe....it works great. I've since taken all the guards off....It's good enough for what I do....I thought about a dimmer switch, or Rheostat myself, and saw this, It was easier....

Keep experimenting and sharing! Best of luck and don't forget to wear eye protection. Grinding aluminum on a wheel is also a no-no as the wheel will heat up and explode.

This -could- be how a variable speed grinder works, though the dimmer they use is likely heavier duty than this. And yes, you risk burning out the engine if you are not careful. Basically the lower you go in rpm, the less load you should be using.

Other variable speed setups would either use a discrete number of speeds (which can be implemented using switches by shorting / combining coils in a certain way) or best case a frequency drive. The frequency drive is the best, and also more expensive solution.

But for light duty low cots, this works like a charm.