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Eastern Carolina Plastic Modelers
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Last Update: 12 Apr 2009

How to Build a Rotary Tool Speed Controller
Brian Vinciguerra

[article image]

WARNING: The following tutorial includes information about wiring electrical switches. Electricity is dangerous and if not respected can cause injury or death! Before following the instructions in this tutorial you should have a basic understanding of electrical wiring. The author and ECPM are not responsible for the improper use of the information provided herein.

Now with the disclaimer out of the way, let's get down to business!

We have all been there wanting to speed up the humdrum process of modifying parts, sanding fiddly bits, drilling holes, you name it and the versatility of the rotary tool comes to mind. But for most of us the 28,000 or more RPM's are way too much and ends up creating more damage to our project than manual means. If only there was a way to have direct control over the speed of the rotary tool. Some of the newer Dremel tools come with built in speed control, the one I have even the lowest speed is too fast for styrene plastic. What to do? What to do? I know! I will make one.

I have to credit Scott Garvin at for the idea. He mentioned it in one of his YouTube videos and I thought it was ingenious. The idea has been floating around the net for some time and if you Google it you can find 36,200 hits for Dremel speed control. But why go to all of that hassle if you have a few items lying around, a couple of simple hand tools and some basic knowledge of wiring.

[article image] Here is what you will need to make this speed control for your rotary tool:
  • Scrounged Heavy Extension Cord ( I used a replacement cord and plug because I didn't have a short extension cord that I wanted to modify).
  • Dimmer Switch ( I used a single pole dimmer switch available at LOWE's for $4.93).
  • 4 wire nuts.
  • 2 Electrical cord retainers for the outlet box.
  • 1 PVC outlet box.
  • Flat tip Screw driver.
  • Cross tip screw driver.
  • Wire strippers.

[article image] Step 1: Prepare the extension cord

If you are using a scavenged extension cord this is the easy part simply cut the cord in where you want to splice the junction box and dimmer switch in line with the cord. I am using a replacement cord and plug so I have to install the replacement plug on the end of the cord, and then cut this cord where I want to splice in the junction box. (Remember to follow all of the manufacturer's directions when installing the replacement plug to ensure that you are using the correct polarity, otherwise disaster will ensue)

[article image] Step 2: Prepare the Junction Box

The dimmer switch takes up the majority of the space inside of the junction box so it is important to select the correct holes to remove the knockouts on the junction box. After removing the knockouts install the cable retainers into the box and route the prepared cable ends into the box.

I removed the knockouts on the base and on the side so that the cable can be routed into the junction box and still allow room for the dimmer switch to seat all the way into the box.

[article image] Step 3: Wire the dimmer switch to the cable.

Notice on the dimmer switch that there are two black wires and a green wire. When making your splice into the cable be sure to follow the manufacturer's directions for the switch that you purchase.

When wiring the black wires from the switch to the extension cord each black wire attaches to only one of the black wires from your extension cable. This switch is placed in-line on your extension cord

[article image] When wiring the green wire from the switch to the extension cord you should have three green wires twisted together (the green wire from the dimmer switch and the green wires from your extension cord that you are rejoining all in the same connection.)

When wiring the white wires you are simply rejoining the white wires that you cut when you made the cut in the extension cord.

This picture illustrates what I am trying to say.

Step 4: Button it up!

Carefully place all of your connections into the junction box, and attach the dimmer switch to the box using the provided screws. Ensure that you cinch the cable retainers down to minimize the possibility of your cable pulling out of your junction box and creating a shock hazard.

You now have a fully functional speed controller for your rotary tool that should look something like the article lead picture.

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