WHY would you want to make your hot glue gun cooler?

Well, hot glue guns are great. They will stick just about any two materials together with a strong and flexible bond which hardens in less than a minute. But . . .
I occasionally make radio control model planes out of Depron foam and EPP sheets (foamies) and these materials have quite a low melting point. At its normal temperature, hot glue will spread across the surface of the foam and eat into it causing bubbles of gas to blow into the glue and making a very messy joint. The same is true of fanfold foam and Styrofoam (expanded polystyrene) which is much the same thing and melts into nothing at full heat.

Look at the photo. At its normal temperature my gluegun makes a mess of the foam. Turning down the heat reduces the bubbling until the glue is below the foam's melting point, which still gives a solid join much stronger than the foam, but so much neater. With my modified glue-gun I can now make repeatable neat joints in the foam with no distortion due to overheating.

Temperature controlled glue guns are available, but these are still too hot for Depron or EPP. You can also get adjustable guns, but these come in way more expensive than my idea here. There are also cool-melt guns, but I've never found them to have the adhesive power of hot glue.

*** Warning : This project uses potentially lethal mains voltages ***
*** Safety should be the main consideration during construction ***

^{( Contrary to what appears on the blog sites which have picked this up, I did not ruin

several sheets of depron using too hot a glue gun. I'm not quite that slow a learner #;¬)}

Step 1: What You Will Need

Unless you have a particularly long mains lead on your glue-gun, you will need a length of mains wire with a mains plug on the end. You'll find one around the house somewhere, probably attached to a defunct gadget. It should be no thinner than the lead to the glue-gun.
You will also need a cheap switched light dimmer (£5, $8) which you can get from any DIY shop electrical department. Get as low a power one as possible; 250W is much more than enough. My glue-gun is 35W and the dimmer cuts off about 1/5 travel which is probably due to it being below the minimum (60W rating). Not a problem as this is below the glue melting point.
As I'm in the UK I'm using 3 pin mains plugs and a 240V dimmer but obviously you would use items suited to your local mains. You will also need a standard single surface mount plastic back-box to mount the dimmer in. Additionally, you'll need the trusty soldering iron, a couple of lengths of heat-shrink and something to provide strain-relief on the cable; I used a cable tie here.

Step 2: Construction

The wiring of this is really simple :
If you have a permanently wired glue-gun or if it's the removable lead type, cut the mains plug off and cut the additional lead at the equipment end. This gives you two leads - one which will go to the wall socket and the other to the glue-gun.

Strip back the insulation and connect together the two neutral wires (blue in the UK / Europe, white in the US / Canada) - I twisted and soldered the wires then put an overlong sleeve of heatshrink over. I doubled back the heatshrink and shrunk another piece over it. Break out one of the openings in the back-box and feed the cables through. I used larger diameter heatshrink over these to reduce abrasion of the cable insulation.

The live / hot wires (brown in UK / black in US) go to the dimmer switch. The feed from the plug goes to the AC symbol (~) and the wire to the glue-gun to the other (L2) terminal. Bare the ends and screw down tightly making sure there are no exposed conductors. No earth connection is required here as there are no metal parts accessible to the user.
To stop the wires pulling out of the box I've put a large tie-wrap tightly around the cable, too large to go through the cable hole.

Screw the dimmer plate to the back-box, plug it in, turn it on and you're ready to glue!

Step 3: Finishing Touches

Now you've got an operational controllable glue gun, lets just finish things off :

Calibrate the gun with a piece of scrap foam. Set the dimmer to half way and wait for a few minutes for the temperature to stabilise. Rest the gun nozzle on the foam and if it fizzes and sinks through, turn the dimmer down a bit, wait and repeat.
The optimum temperature will be the point where the nozzle just marks the foam surface. Mark this on the dimmer dial.
Depron and EPP have about the same melting point so can use the same setting, but if you're working with other materials you may want to calibrate for these as well. I find about 1/3 setting gives the best results for the foams I use.

Roughen up the underside of the dimmer box near the corners; I had four handy raised areas on mine. Put a small blob of hot glue (not too hot) on each one, turn the box over and put it onto a sheet of glass or polished metal. This will flatten the blobs and level the box. Wait a minute for things to cool and then twist off the box. You now have a box with non-scratchy feet. You could use this idea on many items which need levelling or making non-scratch (e.g. ornaments on varnished shelves).

Dribble a bit of glue around the cable entry. This will fix the cable in place and stop it abrading. It will also stop liquid entry if you have one of those unfortunate workbench / coffee cup incidents.