Can I use a light dimmer on a Scroll Saw motor?

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.

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

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.

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.

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......

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A resistance dimmer (gets hot) might work. Some triac dimmers might work. L ook for a variable fan speed control. That would be the ticket. Noting all the while that the scroll-saw motor is not designed for variable speed and will likely heat up in short order. Many motors 'attempt' to draw as much c urrent as they need to operate - and why it is that motor-type items hate b rownouts.

Peter Wieck Melrose Park, PA

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Speaking of heat, many motors have an internal fan on the shaft. If ran too slow that fan will not pull in enough air and the motor will overheat.

Company I worked for burnt up 2 motors of about 100 HP running it on an inverter to slow it down before I looked into it. Put an external powered fan on the motor and all was well.

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Ralph Mowery

The motor is probably the universal series wound type, which works nicely with a triac type 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.

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.

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.

No. Too small.

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

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:

Jeff Liebermann 
150 Felker St #D 
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Jeff Liebermann

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.

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Clifford Heath

This may or may not work, but it is a true triac speed controller

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Foxs Mercantile

I've used various light dimmers to control various table fans, built between 1935 and ~1990. The first hour or two, several times I check each fan to see if it's overheating. None have, but one out of 5 or 8 didn't work at all on any setting of the dimmer. The other 4 or 7 worked fine. I never slow the fan to stopping speed or even close. I like my fans to be so slow I don't hear them, but they still blow quite a bit of air at that speed. . I've done this for 30 years, and right now there's a 3-speed 12" fan blowing on me. Even the low speed was too high, theough iirc I have this on speed 2, and dimmed from there. Been using it all summer for at least 3 years.

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