DIY Variable Speed Controller for otherwise single speed hand tools?

Steve Thomas

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Jul 9, 2004, 3:48:42 PM7/9/04

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Greetings:

I have a little Black & Decker Sander that is just the right size for
detail work, but sometimes on finer pieces of wood, it's too
aggressive (13,000 orbits per minute).

I was wondering if I built a device from a standard 110V Lamp Dimmer
Switch (basically a short extension cord with a single gang work box
inline to vary the power to the device) if this would accomplish my
task.

Could this cause damage to the motor itself?

I know that Dremel makes a foot-pedal switch that can be used to
control their tools in a similar fashion, but I am concerned that a) a
larger motor might not work with it and b) I want to be able to set
the speed and then forget about it, not keep my foot on a pedal.

Thanks in advance for your help.

Steve

Nirodac

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Jul 9, 2004, 9:54:13 PM7/9/04

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I wouldn't use a light dimmer. But, most hardware tool stores sell variable
speed controls that you can plug your sander into, then plug the other end
in to the wall outlet. They have a rotary dial to set the speed. They are
intended for routers, but would work just as well on a sander. They are
built for inductive type loads (like motors) and not resistive type loads,
like light dimmers.
Here's one example;
http://order.harborfreight.com/EasyAsk/harborfreight/results.jsp

"Steve Thomas" <stevent...@yahoo.com> wrote in message
news:811942d0.04070...@posting.google.com...

ch...@nospam.com

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Jul 10, 2004, 1:01:26 AM7/10/04

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On Sat, 10 Jul 2004 01:54:13 GMT, "Nirodac" <nir...@hotmail.com>
wrote:

>I wouldn't use a light dimmer. But, most hardware tool stores sell variable
>speed controls that you can plug your sander into, then plug the other end
>in to the wall outlet. They have a rotary dial to set the speed. They are
>intended for routers, but would work just as well on a sander. They are
>built for inductive type loads (like motors) and not resistive type loads,
>like light dimmers.
>Here's one example;
>http://order.harborfreight.com/EasyAsk/harborfreight/results.jsp

In most cases, these speed controls are nothing more than a light
dimmer. Perhaps with a bigger triac to handle the startup surge
better, but a dremel is a pretty light load anyway.

-Chris

Suraj

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Jul 10, 2004, 1:30:56 AM7/10/04

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stevent...@yahoo.com (Steve Thomas) wrote in message news:<811942d0.04070...@posting.google.com>...

Ya,I agree that 13000 rpm is too much for fine woodwork.But it depends
on the kind of abrasive you use.Your solution of making use of a
dimmer switch will work perfectly.But make sure that the load of the
motor matches the current rating of the switch.Again if you use a
fixed step switch,then you have a lesser number of speed selections.So
try to use a dimmer which has a rotary knob (a preset which is
adjusted to change the firing angle of some kind of thyristor inside
it).That should take upto 200W easily.
I dont see any reason for this process to damage the motor.But it may
damage the switch if you dont comply with the ratings:-)
Now,if you want to go for a serious and permanent solution,you will
have to use control circuits based on microcontrollers,tachometers and
thyristor based power electronics stuff.

regards
Suraj

Fernan Bolando

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Jul 10, 2004, 7:11:54 AM7/10/04

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I have a queastion, Doesn't light dimmer work by delay gating of
the ac cycle? which means the output is no longer a true sine wave.

I dont think this suitable for induction motors, But since high torque
power tools are not induction motors.

,Fernan

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