Grinder Speed Reduction

[fritz eng]

I have a Ryobi 8" dia. 5/8" arbor grinder rated for fixed 3600 RPM. Is there a way to convert this to a variable speed grinder? Looking to change to CBN grinder wheels and it appears the slower speed (1800 rpm) is the preferred speed for sharpening tools. Does the RPM make a major difference when sharpening plane irons and chisels other than to minimize burning? What difference does changing to a smaller diameter wheel make? Thanks

[Jim Becker]

I have a Ryobi 8" dia. 5/8" arbor grinder rated for fixed 3600 RPM. Is there a way to convert this to a variable speed grinder? Looking to change to CBN grinder wheels and it appears the slower speed (1800 rpm) is the preferred speed for sharpening tools. Does the RPM make a major difference when sharpening plane irons and chisels other than to minimize burning? What difference does changing to a smaller diameter wheel make? Thanks

It's an induction motor, so honestly...the easiest way to solve this is to buy a 1750 rpm grinder to use with those wheels. You cannot use any kind of common "speed control" on an induction motor. There may or may not be a VFD that could potentially control a single phase motor (I don't know...) but the cost would likely be more than a common, 8" 1750 RPM grinder "off the shelf".

[Ken Fitzgerald]

I have a Ryobi 8" dia. 5/8" arbor grinder rated for fixed 3600 RPM. Is there a way to convert this to a variable speed grinder? Looking to change to CBN grinder wheels and it appears the slower speed (1800 rpm) is the preferred speed for sharpening tools. Does the RPM make a major difference when sharpening plane irons and chisels other than to minimize burning? What difference does changing to a smaller diameter wheel make? Thanks

For the record, I own an 1850 rpm grinder and like it. That being said, by those who are experienced on a dry grinder, speed is argued regularly. If the wheels require a slow speed grinder, the cheapest way I know is as Jim suggests, buy a slow speed grinder. If the wheel manufacturer doesn't suggest or recommend a slower speed, try it. Like most things, experience and practice are required to be skilled at using a tool.

[Richard Coers]

Are you going to sharpen HSS tools? If you are doing plane irons and bench chisels, you are sharpening high carbon steel and if they aren't really hard, you may have a fouling problem with the CBN. Good white aluminum oxide wheels are easily dressed with a diamond dresser. And with a light touch on the grinder it will work very well sharpening tools at high speed. I wonder about that 3,600 rpm. All I've seen is 3450 and 1725. I've taught a lot of people and done demos at regional symposiums. A very small majority understand what a light touch is, and even less are patient with the process. Sharpening requires leaned skills and techniques. IT'S NOT LIKE YOUR DAD SHARPENING LAWN MOWER BLADES!