Admit it, you’ve used the hot glue analogy when explaining 3D printing to a layperson.

“Grandma, it’s like a hot glue gun, but with plastic! It just squeezes layer upon layer, in a specific pattern, until the three-dimensional part is complete.”

“Oh, that’s nice, dear,” she probably replied to humor you.

Jokes aside, an FDM/FFF 3D printer’s extrusion process is very similar to that of a hot glue gun. So, why not use the hot glue gun for 3D printing? Jón designed a special extruder to do exactly that and it is more than just a gag for YouTube.

The Idea

Like the thermoplastic materials that we all use for 3D printer filament, hot glue can change states from solid to liquid and back while retaining its chemical structure. Jón’s goal was to control that process well enough to print at an acceptable quality.

That would have been pretty easy to achieve if the hot glue were reformed into filament and spooled up, as shown by Stefan of CNC Kitchen. But Jón wanted to keep it in the standard stick form factor. That proved to be a much greater challenge, but it introduces the potential for all kinds of benefits.

The Advantages

Hot glue comes in those sticks for a reason: for rigidity to make feeding reliable with very simple mechanisms. That can be applied to 3D printing, too. Doing so would solve many of the problems associated with very soft and flexible materials, as well as brittle materials.

Some materials, like the TPU used for flexible filament, are notorious for being difficult to print. The filament has a tendency to bunch up and jam. And most TPU filament is actually fairly stiff, because softer and more flexible materials simply wouldn’t work. An extruder that works for hot glue sticks would also work for very flexible materials.

The stick form benefits would be even more apparent with brittle materials that can’t be spooled at all. Chocolate is a good example and that has been a major issue for those seeking to build chocolate 3D printers. But in the same form factor as a hot glue stick, chocolate would be easy to feed and extrude.

Even staying within the realm of hot glue, there are a surprising number of interesting options. From numerous colors to exotic formulations, the world of hot glue has quite a bit to offer.

The Extruder

Of course, Jón had to actually make an extruder capable of pushing hot glue sticks for any of those benefits to matter. Fortunately, he already designed an extruder that he could repurpose for this job.

That extruder has timing belts in place of the standard gears. They act almost like miniature and opposing conveyor belts, so they can grip any material by sandwiching it securely in-between the belts. That arrangement has the advantage of boatloads (Benchy loads?) of surface area contact for tons of grip, without squishing or grinding the material.

Those attributes make it perfect for this job, Jón just had to tweak the design a bit to work with the hot glue sticks.

Adapting the Design

Jón had to resize the extruder to work with the glue sticks, which are obviously much thicker than any filament on the market. But he also had to go further to create a feeding mechanism for the sticks.

A normal glue stick only provides enough material for a relatively small part, but ultra-long sticks wouldn’t be practical. So, Jón had to devise a way to insert new sticks into the extruder automatically. The feeder he invented uses a magazine-style mechanism to push a row of sticks to a chute, which indexes and drops sticks down into a funnel-like opening on the top of the extruder.

Interestingly, that feeder relies on gravity for both the stick drop and for putting pressure on the magazine. Two big fishing weights help with the latter.

A Big Roadblock

Even with the well-designed extruder, Jón ran into a major problem: heat creep and leaking.

In the 3D printing community, we creatively refer to the part that gets hot as the “hot end.” But that is a bit of a misnomer, because only one end of the hot end should be hot (the hot end’s hot end). The other end should be cool enough that it won’t cause the filament to begin its glass transition. That’s why there is a big heatsink in the middle above the heat break, usually paired with a fan.

If the cold end of the hot end gets too hot, which we call “heat creep,” the filament will deform before it is fully into the hot end tube. That will almost certainly cause leaking around the top and an inevitable clog.

Leaking

Jón experienced that issue for two reasons: he wasn’t using a “real” hot end and it wasn’t sealed properly.

There aren’t any manufacturers making hot glue stick-size hot ends, so Jón was happy to find that his Dremel hot glue gun contained something similar to a 3D printer’s hot end. It is simpler than a “real” hot end and lacks cooling hardware, but it isn’t wildly different. It even accepts a cartridge-style heater—though that is an AC mains-powered cartridge larger than the kind we use for 3D printers. Jón added a sleeve to get a tight fit with standard DC-powered 3D printer hot end cartridges, solving that issue.

He transplanted that onto his extruder, treating it like a normal 3D printer hot end. But the leaks wouldn’t stop and that was further exacerbated by Jón’s accidental failure to place the preceding silicone tube’s spring clip in place.

The Solution

After multiple revisions and continued printing failures, Jón decided to attempt a surprising solution. Instead of putting the hot glue gun’s “hot end” into his extruder, he attached the entire bottom end of the gun to the extruder.

That required some milling of the gun’s plastic housing for mounting purposes, but it looks pretty cool and can’t be mistaken for a regular extruder/hot end.

Jón even switched back to the heater cartridge that came in the glue gun, which eliminated all temperature control—it just plugs into AC mains power and heats up to its max temperature. But with the silicone tube’s spring clip back in place, Jón was finally successful and printing in hot glue with respectable quality.

Future Plans

Though Jón can now print in hot glue of all kinds and colors, he isn’t planning to stop there. As previously mentioned, this idea has a lot of potential beyond just the novelty. For that reason, development will continue.

Jón’s biggest goal is to design and fabricate a custom hot end for this application. That should solve the heat creep and leaking issues, while being compatible with standard heater cartridges.

A purpose-built hot end should also dramatically improve quality. It would make the extrusion much more consistent and enable the use of nozzles in differing sizes, with geometry optimal for 3D printing.

If Jón can pull that off, we may see this stick-based 3D printing concept gain real traction for specialty applications.