[TheForge] rpm/horsepower

[Schade]

Thanks Ries.

Bob
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On Oct 6, 2004, at 4:16 PM, Ries Niemi wrote:

> Where the heck did you get a 1750 rpm bench grinder?
> Grinding wheels are designed and rated in surface feet per minute, 
> with the average stones wanting to run around 5000sfpm.  A 6" grinding 
> wheel on a 1750rpm grinder is running at about half that- too slow, in 
> other words.
> Commercially, almost all bench grinders are 3450 rpm until you get up 
> to the big dogs- say 12" or 14", at which point they drop down to 
> 1750.
> Now if you are gonna use this for buffing, or wire brushing, that 
> might be different. But for grinding, in a 6" or 8" size, you want 
> 3450, and thats what they make.
> As far as torque goes, yes, its true that a slower motor has more 
> torque for the same horsepower. But you need the speed, so you do need 
> a bigger motor. I have a 1 1/2hp Jet that I am quite happy with- cant 
> seem to slow it down.
>
> If you are wet grinding woodworking tools, of course, throw all this 
> out the window, and buy a special machine for that. But for general 
> purpose sharpening and grinding, 3450 is right.
>
> ries
>