Craftsman 8" variable speed grinder - problem

[Philip Ralph]

I have a Crafsman 8" variable speed grinder that I purchased on the cheap (60.00), when I first started using it, I set the dial to 1800 and started the grinder. It started up great and keep the speed for a couple seconds and then jumped up to full bore. I tried turning the dial on the grinder, but now it just runs at full speed no matter what I do. My question is, does anyone know what might have happened and/or how to fix it? I am thinking about getting a dimmer switch to plug the grinder into just so I can get it back to the lower speed. This is the grinder... https://www.sears.com/craftsman-professional-variable-speed-8inch-bench-grinder-21162/p-00921162000P

 

[Lamar Wright]

Phil, sounds like the variable speed rheostat may have gone bad? You can probably order a rheostat from Craftsman. Shouldn't be hard to fix.

 

[Bill Boehme]

A dimmer won't work and would ruin the dimmer if you hooked it to the motor. The problem is that one of the electronic parts has failed. It's probably not worth the cost of having it repaired and cost wise you might be better off getting a low speed grinder like the Rikon.

The motor in your grinder is a hybrid between a two-pole and four-pole motor. The synchronous speed of a two-pole motor is 3600 RPM and 1800 RPM for a four-pole motor. In this hybrid design, the electronics switches between the two configurations to run at intermediate speeds.

I think that the variable speed thing is more of a novelty than something of actual value as far as sharpening woodturning tools is concerned. Unless your grinder is vibrating it should be usable running at high speed.

 

[Philip Ralph]

Thanks for the help guys, one more thing, do you think I will be alright putting a CBN wheel on my current grinder? I don't want to replace the grinder if I don't have to, especially since the CBN wheels can cost as much if not more than the grinder itself.

 

[Bill Boehme]

Thanks for the help guys, one more thing, do you think I will be alright putting a CBN wheel on my current grinder?

Definitely, no. As a bare minimum you need 1/2 HP and 3/4 HP or more is preferable. That grinder motor is probably somewhere around 1/4 HP.

 

[Finn Posner]

Phil - Here's my 2 cents worth. I have the same grinder and while I've not had this problem, I rarely if ever turn up the speed. So based on that comment and Bill's suggestion you could get a new fixed slow speed grinder and be perfectly happy for a long time. The Rikon's from Woodcraft are on sale frequently and are 1/2 HP.

 

[Philip Ralph]

Live and learn, sometimes you do get what you pay for. I guess I will try to get my money out the grinder and look for the Rikon to go on sale. Thanks again for all the help and advice.

 

[Perry Hilbert]

I remember my uncle sharpening his lathe tools on an old foot peddle grindstone. We have it soooooooo bad.

 

[John Torchick]

What Finn said. I doubt if you could find the part as Sears has a habit of running out of parts after a few years, especially if it is something that is prone to go kapooey frequently.