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Using a dimmer switch to slow your Dremel


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I've got an old Dremel speed control device that I picked up on eBay years ago.  It might be the same as a dimmer, you plug the Dremel into the speed control then plug that into an outlet.  The instructions warn against using it with a Dremel that has built-in speed control.  I figure they (Dremel) know what they are talking about where their products are concerned, and didn't see the value in risking the variable-speed tool.  I've had this one about thirty years and it's as good as new.

I instead bought a cheapie single-speed Harbor Freight rotary tool to use with the speed control.  It takes the same bits as the Dremel (albeit only one shaft size; no extra collets) and I can slow it down to nothing when needed.   

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I have also used it with an X-Acto soldering iron with the "hot knife" attachment, to keep the blade temperature down.  It'll never do precision cutting, but it has come in handy on occasion.

Edited by Mark
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The older variable-speed Dremel tool (model 395) internally use a circuit similar to a dimmer switch to control the speed, but it is designed for inductive loads. The motor inside that tool is an inductive load.

Standard dimmer switches are designed for incandescent light bulbs. Those are resistive loads. I woudl not recommend using a standard dimmer switch for a Dremel.

There are variable speed controllers designed for inductive loads.  For example a speed controller for a router will likely do the trick (router motor is also an inductive load).

Here is one for 18 bucks: https://www.harborfreight.com/router-speed-control-43060.html  Or, Google for router speed controller for more choices.

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Don't know if there is a difference between Dremel and a Black & Decker hand held grinder.  The B&D has a motor mounted under the bench with a flex-shaft going to the hand held grinder.  I have used it for many years using a light dimmer as a speed control with no adverse effects that I noticed.  I have in the past couple of years switched to a Dremel (Christmas present from my wife) and have sort of retired the B&D, although it is still available if needed.

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Does the Black & Decker grinder have a speed control built in, or is it a single-speed unit?  I'm thinking that the ability to use a speed control attachment will depend on whether or not the tool already has one built in; that is, if one is already part of the tool, then an external one should not be used with that tool.

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I had an ancient Dremel as a kid. My dad had a plug-in speed controller in his wood shop. I tried it with the Dremel one day, and it blew the circuit breaker for the basement. I think there's some electrical reason for this but electricity might as well be a foreign language to me. At any rate, I never tried it again. 

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Greg, before I got my pedal speed control for my Dremel (variable speed) I used a lighting rheostat for a long time.  Wore out two Dremel motors with it, (from use not the dimmer switch).  
I used a regular old dial light dimmer switch which I used a male and female plug at either end with a light switch box, dimmer and wall switch cover in the middle.  Made from a heavier gauge extension cord, about five feet, dimmer and three feet to the female plug.  This type of setup will run lower RPM’s without heating up, at least my set up would, you have to start at a higher speed and dial it down to the speed you need for the material you are cutting.  
It works great for those really small burr bits gives you a lot of control.  Hope this helps, real time use versus full time opinion!  

I built the set up when I was a poor college kid with lotsa time and not much extra money. I used that set up for probably fifteen years, I think it’s still in my garage still hooked up to a working variable speed Dremel!

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Have you guys ever replaced the brushes in those dremels????....

Real easy to do... Those brushes are only good for about 60 hours of continuous use... You could buy new ones for about 4 er 5 bucks at any of the Lowe's or home Depot... You could swap those out in about 5 minutes...

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As an IBEW electrician for 20+ years I can tell you that you want to use a fan speed controller instead of a light dimmer switch.  The basic electrical reason for this is that a light dimmer turns on the light low, then brightens the lights as you turn it up, and this is not good for a motor.  A fan speed controller turns the motor on at full speed, then slows the motor down as you adjust the speed, this is better for a motor.  I made a simple speed controller from parts you can get at most hardware stores.  I used a fan speed control switch, 120V receptacle, a 6' power cord, a 4 sq galvanized electrical box, a 4 square box cover for a receptacle & light switch and a clamp for the power cord to the box.  I think there are a few online instructions on building one from these parts.

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3 hours ago, Pete J. said:

I don't want to insult anyone, but why would you go through all that, when you can get a new corded variable speed Dremel for about $45?  Seems like a good investment to me.

 Because (in most cases, possibly not all) the slowest speed available with the internal control is still faster than what you want.  I think mine has a "slow" speed of 5,000 rpm.  In fact, with that tool, I seldom go beyond the minimum.

With the external speed control and cheapie Harbor Freight rotary tool, I can slow it down to near nothing.  Better for resin (no flying dust to inhale) or for removing molded-in detail like exhaust pipes.

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