On Tue, 27 Feb 2007 15:36:30 GMT, "Phil-in-MI" NO Spam &
pam wrote:

Just a guess on my part:

Portable tools need lightweight motors. The type of motor traditionally
used in circular saws is synchronized to the frequency of the prime AC
power. The only way to change the speed is to change the frequency from 60
Hz to say 40 Hz.
These are cheap, loud, and powerful motors for the weight. Great for the
construction industry.


You are describing an induction motor (synchronized to the frequency
of the prime AC), which delivers less power for its weight. Table
saws with belt drive typically use induction motors because weight is
not an issue and there is less maintenance (no brushes to replace).

Most portable power tools use some variation of what is usually called
a "universal" motor, which has brushes and a commutator. These motors
have a much better power-to-weight ratio than the induction motor.
The "universal" designation comes from the fact that many variations
can be run on AC or DC (not a major concern today, but was in the past
- DAGS on "death dealing AC" for some history)

John