On 02/07/17 03:34, Jeff Liebermann wrote:
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

A dimmer-style control provides poor low-speed running. It might not
matter for a scroll-saw, which doesn't need to operate at very low
speeds.

However, the same circuit made with an SCR can work. Instead of
putting the motor in the anode leg, put it in th cathode leg (the
side the gate is on). Reverse EMF gives you very good speed regulation
down to very low speeds.

I don't know if it's possible to do the same thing with a Triac circuit.

Clifford Heath.