On Friday, February 15, 2013 10:47:50 PM UTC-7, Steve B wrote:
I am going to cannibalize a Sawzall to crack pecans. I need
to slow it down. If I use a dimmer, will that be adequate,
and work? Or do I need to go with a larger rheostat?

Forget about a rheostat because you'd need one rated for at
least 1,000 watts, maybe 1,800W. Most light dimmers are
also limited to about 600W, an exception being....the dimmer
built into your Sawzall. Consider cannibalizing it by
replacing its potentiometer (variable resistor) attached to
the trigger with regular rotary potentiometer of the same
ohms rating, taper (linear or logarithmic), and power
rating at least as high (most chassis mount pots are
just 1/2W - 1W, while wirewound ones are 5W). However
any external potentiometer will have to be electrically
isolated because it will be attached directly to a 120VAC
source. You'll have to attaching it to something like
plastic or wood and make sure its metal shaft can't be
touched (plastic knob with NO set screw sticking out --
the set screw should be sunk deep in its hole and the
top of the hole covered with plastic). Another
possibility is control through something optically
isolated. Here's something that explains it:

http://www.fairchildsemi.com/an/AN/AN-3006.pdf