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View Full Version : Grinder question for ya.......


Bill White
12-14-2011, 11:17 AM
Is there an electrical modification that will allow speed control? I have an older 7" bench grinder (3600 rpm). I know that a router speed control won't work 'cause it has an induction motor. This is an excellent grinder and it serves me well. I just have to be careful not to burn metals. Was just wonderin' if there was such an option available.
Bill
Steve Schlumpf
12-14-2011, 12:01 PM
Bill... I believe your router is a universal motor and uses brushes. Your grinder is an induction motor and the router control will not work on it. As far as I know, there is no way to vary the speed of the motor as it is a function of the way the primary and secondary coils are wired. I could be wrong... but I don't think so.
Steve Baumgartner
12-14-2011, 1:09 PM
Your grinder almost certainly has an induction motor, which means it is "almost synchronous" to the line frequency (it has to slip a little below line frequency to create induction). The only way to vary the speed is to vary the line frequency, for example, with a variable frequency drive.
Dan Forman
12-14-2011, 1:20 PM
Might be a good excuse to get a CBN wheel, they grind very cool.

Dan
terry mccammon
12-14-2011, 3:19 PM
Here is a quick link to single phase variable frequency drives. http://www.anaconsystems.com/text/opti_e2.html At the price point you could buy two high quality grinders for that price. If you are handy with electronics and want a project you can build a pretty cheap VFD, yourself, but I can't encourage it.

Good luck.
Jack Mincey
12-14-2011, 4:04 PM
I use a 7" high speed grinder for most of my scrapers in my school shop. I haven't done the math but feel that while the speed of the 7" is definitely faster it isn't that much faster than a slow speed 8" wheel as far as surface speed. I would have to guess that it is some where between a high speed and slow speed 8" grinder. A good clean wheel helps to reduce the heat more than anything. My 7" grinder has a pink wheel which I got from Woodworkers supply and it works very well, but it is closer to a 6 1/2" wheel right now which slows the surface speed down a little more.
Jack