Shopsmith Forums

algale wrote:This is an interesting issue.

As you have ably pointed out there is a simple mathematical correlation between HP and torque and rpms. Presumably you need a combination of all three to spin a 10 inch diameter, 1/8th inch metal blade through a piece of wood of a given thickness and hardness. But is it six of one half a dozen of the other? Or does it matter which combination of hp/rpms and torque you use to cut a given piece of wood using a given blade?

The first and obvious thing that jumps out at me (and which 8iowa mentioned) is the lowering rpms to generate more torque reduces the speed at which you can make the cut. Not a big deal unless you are a production shop (or a hobbiest in a big hurry). I would guess secondarily, rpms/speed will correlate with the amount of heat generated during the cut. Are there other factors that have a real world impact on woodworking?

Or put another way, are there certain operations for which you need a 3HP table saw running at 3450 RPMs that simply can't be accomplished on a 1.125 HP Mark V running at 1295 RPMs?

nuhobby wrote:These would be the obvious things, but there's always the 'reduction to absurdity' argument of using an even lower-power motor at a lower-yet RPM setting, which breaks down at some point. At the very slower blade speeds there's probably non-linear effects. I'll bet that the dynamics of wood-chips efficiently ejecting from the kerf would change if the blade goes too slow. And with very low blade RPM, the ability of the blade/motor to keep a consistent blade-tip speed via inertia (each time a blade-tip hits wood) would suffer. A nice running blade is a synergy of many optimized factors.