On Sat, 01 Jul 2017 00:42:23 -0400, wrote:

Most of the new scroll saws have variable speed. I have an old Delta
from somewhere around the 1970s. The saw works fine, and is built much
better than the new ones which have a lot of plastic parts. But it has
one drawback, no variable speed control.

The motor is probably the universal series wound type, which works
nicely with a triac type speed control:
https://en.wikipedia.org/wiki/Universal_motor#Speed_control
Make sure your unspecified model saw motor does not exceed the current
ratings of your unspecified light dimmer or speed control. You're not
going to hurt the motor doing this, but you might blow up the speed
controller if it's under-rated.

I've seen schematics for motor speed controllers, but I already have too
many projects to do.

Right. There's never enough time to do it correctly, but always
enough time to clean up the mess you create after it doesn't work.

Is there any reason I can not use a regular light
dimmer to control the speed? I would use a dimmer rated at 600W or
greater. (The saw runs on my 300W inverter in my car, so it's not a huge
power user).

Ummm... why do you have a scrolling saw in your car?

If you have a clamp on amps guesser, measure the peak current of the
motor. The light dimmer is probably ok for the motor running current,
but I would be concerned about the higher starting current. Check the
nameplate on the motor for real numbers.

I also have some old electric drills that have bad motors or stripped
gears, which have variable speed switches. I suppose I could modify one
of them for this use too, but since I need two hands for cutting the
wood, I cant be holding a trigger switch. That's why a light dimmer
seems most useful. I can just dial the speed I want and dont need to
touch the dimmer unless I want to change the speed.

No. Too small.

Plus a dimmer could just be mounted in an electrical box, with a
receptacle next to it, and I can just plug the saw into that box.

Good idea. When the light dimmer explodes, the metal box will prevent
the schrapnel from doing much damage.

But I am asking about this because I am a little concerned that the
dimmer could be hard on the motor, since these dimmers are made for
lighting, not motors......

The dimmer will produce harmonics of the 60Hz AC which might need to
be dissipated by the motor. However, the harmonic content is small
and should not cause a problem.

I think buying one of these might be a better idea:
https://www.harborfreight.com/router-speed-control-43060.html
http://www.ebay.com/itm/382139367809

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558