Q. A woodworker is looking at routers and wants to know the merits and differences between amp ratings and HP ratings.

A. (Ellis Walentine) "Horsepower ratings on routers are only semi-useful, and only for comparison purposes. Common sense tells us that a 3 HP router doesn't have the same muscle as a 3 HP cabinet saw. Amp ratings are more objective, but they can't be taken as the final word on power either, since the amount of amperage a universal motor draws is affected by its efficiency and several other factors.

Oddly, when we built a dynamometer to test routers back in '93, we spent a month crunching numbers to try to figure out which measurements were actually useful to prospective buyers. We decided that the best indicator of power was RPMs under load. In other words, how well did the router maintain it's speed under differing load conditions? We applied loads corresponding to light, medium and heavy cutting tasks and measured the draw-down in bit speed with a sophisticated stroboscopic tachometer. The gutsier motors showed only a small drop-off in speed, while the speeds of the weaker motors dropped precipitously, some by more than 65%."