A simple mod turns a cheap hot glue gun (messy) into a precision tool (neat) suitable for more professional and intricate modelmaking and prototyping.

Hot glue guns have a bit of a reputation for clumsiness in the maker community. The liberal, messy application of glue in a project tends to be associated with amateurish, quick or kludgey projects (what we in the UK might call bodges), but glue guns are cheap, quick to use, and allow parts to be separated again relatively easily if required. Hot glue can also be useful in sealing against water ingress.

It occurred to me that a cheap glue gun could be easily and rapidly modified to turn it into a precision tool. It's basically just a heating element surrounding a tube through which the glue stick is pushed, and a nozzle. The gun shape is useful in allowing the user to use a trigger action to force the stick through the heater, but not necessary for the actual application of glue, nor desirable for the precision control needed. A pen shape would allow more precise control.

This is still to some large extent work in progress and ultimately, an even better tool will evolve from the simple modded version; I have plenty of ideas for turning this into a real professional product and would appreciate suggestions and ideas from other makers.

Step 1: Prerequisites

You'll need:

- A hot glue gun, preferably one of the smaller types (I've been using a Bostik 'Handy' with 5/16" (7 mm) diameter sticks, but many other types are available).
- Drill, drill bits, screwdrivers, screws, miniature hacksaw, files, etc
- Soldering iron & solder OR solderless mains connectors of some kind
- A metal 'nozzle', such as a ballpoint nib surround, with the end hole smaller diameter than that of the glue gun nozzle
- (Electrical) insulating tape
- Some kind of (thermally) insulating material (I used both a synthetic rubber drinks coaster - not very successfully - and the plastic body of an old soldering iron - much better)
- Non-thermal glue (superglue or similar)

There are many ways the quality of the outcome could be greatly improved by using proper tools and facilities - even taps and dies for thread cutting would make a big difference.

Step 2: Dismantle the Glue Gun

Take the glue gun casing off. You might find it has 'tamperproof' screws; while you could make your own screwdriver bit (as in Make Vol. 3), I just took the easy option and drilled the screws out. Make sure the glue gun's not plugged in if you do this, as the mains cable may be wrapped close by the screw bosses.

Inside the gun you'll find quite a lot of stuff, much of which is the trigger mechanism. We don't need this, so it can be taken out and put aside, along with the case itself. Don't throw the case away, as it may be useful later on.

Step 3: Getting Down to the Basics

This is all you really need: the cast tube/casing/nozzle combination with the heating element in it and mains wires attached. (You may also have a small filament bulb as an 'on' indicator - up to you whether you keep it or not. I didn't). The synthetic rubber sheath round the end where the glue stick is inserted isn't essential, but stops you burning your fingers.

If you plug this in at this stage, be aware that a) it gets very hot very quickly, and b) the device is no longer double-insulated, i.e. the exposed metal is not earthed. A fault in the element may cause the metal to become live.

Step 4: Adding a New Nozzle

I fitted the aluminium nib surround from a ballpoint pen - with a smaller diameter hole at the end - over the original nozzle of the gun, fixing it in place with superglue and, less sensibly, a small screw, and tape wrapped round it all. Don't use the screw, unless you can make absolutely sure that no hot glue will seep out around it when under pressure. Also, don't use solder, because it will start to melt as soon as the nozzle heats up.

It would be better here to use a die to cut a thread on the original nozzle so that the nib surround can be screwed neatly into place, or find another way of attaching it or extending the original nozzle. For example, a very thin tube of the type used on many plastic cement tubes for modelmaking would be much more precise, if it could be attached reliably.

Step 5: One Way of Doing It

At this point, I decided to turn the heating element assembly into a longer, pen-like device. It wasn't as successful as I hoped, so you may wish to go to Step 9 to see how the project developed after this experiment.

Step 6: The Pen-type Version: Making the Barrel

For my pen version, I wanted a barrel, both to hold the glue stick and also to make the product easier to hold when using it. The ballpoint pen from which I'd taken the nib surround also had a barrel which looked to be the right diameter to fit the glue sticks; in fact it needed a little bit of further drilling out due to the slight taper (reaming bits would be handy here) but was a good snug fit inside the orange rubber sheath and the glue sticks slid in and out easily. (Note in the photo here I hadn't yet attached the nib surround as the new nozzle, or removed the superfluous indicator light).

Step 7: The Pen-type Version: How Do You Hold It?

I cut up a Dalsouple rubber hot drinks coaster* to make finger/thumb grip plates, which I then glued in place around the part of the device which felt the most natural place to hold it, and wrapped it all in (yellow) duct tape to make sure it stayed in place. This provided a degree of immediate thermal insulation, such that even when the device had been plugged in for 15 minutes or so, it could still be handled without getting burned.

(*well, it may have actually just been a small sample of one of their floor tiles, but I've been using it for years as a coaster - it's a good move giving that sort of sample away to students!)

Step 8: The Pen-type Version: Testing

With a bit more yellow duct tape, and some grey cable ties to give some kind of crude Dyson-esque aesthetic, I was ready to test the pen-type glue gun (I quickly linked up the mains cables using a couple of chocolate-block connectors).

The results weren't great. The length of the barrel made it difficult to stretch a finger to the end to push the glue stick in - it was OK when there was just a bit sticking out (as in these photos) but when a new stick was in place behind an old one, there was no easy way to push it and hold the finger/thumb grips at the same time. Also, though the insulation didn't get hot enough to burn my fingers, it was still too hot to hold comfortably after a while.

So I decided to go back and rethink a few aspects of the device.

Step 9: The Stubby Version: Better Insulation

I needed better thermal insulation for the part of the device that's actually held between finger & thumb. It occurred to me that the plastic used for a soldering iron body is a reasonably good insulator considering how hot the heating element gets, and how close it is to your fingers.

So I took apart an old soldering iron and cut down the barrel to make a stubby housing for the heating element. Unfortunately, the element was slightly too tall to fit entirely inside the barrel, so I had to cut out a slot in the top; it fitted snugly though.

Step 10: The Stubby Version: More Insulation

Because of the slot cut in the barrel to fit the element assembly in place, I decided to cover the barrel completely, to make sure my fingers wouldn't get anywhere near the hottest bits of metal. A metal cylinder from the neck of a wine bottle fitted tightly over the barrel, followed by a plastic 35 mm film canister, with a hole cut in the base for the orange sheath to fit through.

Step 11: The Stubby Version: Finishing Touches

I added some screws through the body abutting right up to the element assembly, to locate it in place centrally in the barrel, and also to stop the plastic film canister slipping when being gripped. Some spiral cable wrap covered the joins in the mains cables.

The device is now usable: it can be used entirely one-handedly, with middle finger and thumb gripping the barrel (which doesn't get very hot), and index finger keeping a light on the end of the glue stick to help feed it through. It pumps out a narrower stream of glue than the standard glue gun, and feels a lot more like a soldering iron to use.

But there's still a lot that could be improved. It would be great to make a truly pen-like device, smaller diameter, with an even smaller nozzle for really precise applications. The original blue plastic casing from the Bostik glue gun may be useful here, cut down, fitted back around the element to give a neat casing. Oh, and that metal nozzle (and the screws) need to be earthed, or covered with an electrical insulator.

Overall this is a pretty vague, haphazard project, but I think it's produced a reasonably useful device.