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......

 

[pfjw@aol.com]

A resistance dimmer (gets hot) might work. Some triac dimmers might work. Look 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 current as they need to operate - and why it is that motor-type items hate brownouts.

Peter Wieck
Melrose Park, PA

 

[Ralph Mowery]

In article <203d707e-b80b-43d6-85f2-36d0e4cd4b45@googlegroups.com>,
pfjw@aol.com says...

A resistance dimmer (gets hot) might work. Some triac dimmers might work. Look 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 current as they need to operate - and why it is that motor-type items hate brownouts.

Peter Wieck
Melrose Park, PA

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.

 

[Jeff Liebermann]

On Sat, 01 Jul 2017 00:42:23 -0400, oldschool@tubes.com 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 jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Clifford Heath]

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

On Sat, 01 Jul 2017 00:42:23 -0400, oldschool@tubes.com 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.

 

[Foxs Mercantile]

On 6/30/2017 11:42 PM, oldschool@tubes.com wrote:

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).

This may or may not work, but it is a true triac speed controller
<http://www.ebay.com/itm/401361481384>


--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

---
This email has been checked for viruses by AVG.
http://www.avg.com

 

[micky]

In sci.electronics.repair, on Sat, 01 Jul 2017 00:42:23 -0400,
oldschool@tubes.com 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.

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......

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.