I checked our grinder at work today and it is rated at 3450 RPMs and has a 7" wheel and I have not had a problem with burning blades. You can sharpen mower blades free hand on just about any bench mounted grinder. In fact that is what we use at work. With all the funny shaped blades out now days the fancy high dollar blade machine is up on a shelf in back of the shop collecting dust. It was just too much of a PITA to try and set it up for every blade sharpen because no two were alike. And you had to have a mounting jig for every blade shape. It was more like cutting keys than sharping blades. A blade sharpening machine would be OK if all or most of the blades were the same type and shape I guess but I fine a bench grinder works just fine. I have even used a side grinder when some one else was using the bench grinder. By the way our bench grinder is not mounted on a bench. It is mounted on a pedestal (post) which makes it easier to use without the other end of what you are grinding hitting any thing. When you get your grinder built you should post some pictures of it. Have fun and good luck.
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