Not sure will ever resolve bench grinder size or motor no-load RPM speed discussion!
Fact a slow speed grinder 1725 to 2000 RPM's will blue your tool just as fast as 3400 RPM grinder. When sharpening your tools need light pressure & clean wheels to avoid bluing a tool no matter how fast or slow your grinder goes!
Okay to blue HSS while sharpening is a myth!
Only advantage to Rikon 8" ½ HP slow speed grinder is those white friable wheels and when on sale for $100. Today that grinder would cost me about $168 with shipping & sales tax. My nearest Woodcraft store is a three to four hour round trip drive.
Only real advice can give when buying a bench grinder is buy locally and understand merchants return refund policy. That way not paying for shipping & restocking fees if things go south. Read those not so positive reviews as well as favorable on that Rikon!
Amazon.com: Customer Reviews: RIKON Power Tools 80-805 8" Slow Speed Bench Grinder, ,
Not knocking Rikon, getting a bad grinder regardless of brand can and does happen. Warranties very limited, so exchange or refund much easiest way to go!
So if live close to a WoodCraft and Rikon grinder on sale go for it. To me driving 5 to 10 minutes to my Lowe's or Home Depot makes more sense for the money. So either the Delta or Dewalt grinders at Lowe's or Home Depot would work for me and buying a set of wheels no big deal for me! Yes, would have to buy friable wheels or CBN wheel, but that's okay for me.
Shop DELTA Delta 8-in Grinder at Lowes.com
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How do explain returning both birthday presents?