What Is 3D Printing, Actually?

People ask us this on the phone fairly often, and it's a reasonable question. The name suggests something like a paper printer, which isn't a bad starting point, but it misses the important part. Here's the whole thing in plain terms.

A very precise hot glue gun

That's genuinely most of it.

The plastic arrives on a spool as a long strand, roughly as thick as a piece of dry spaghetti. The printer pulls that strand into a heated metal nozzle, where it melts at around 200°C (about 400°F). The nozzle squeezes out a thin line of molten plastic, and the machine moves it around to draw a shape.

The plastic cools and hardens within a second or two of leaving the nozzle. So you get a solid line exactly where the machine drew one.

One layer at a time

Here's the part that makes it three dimensional.

The printer draws a flat cross-section of your object, about 0.2mm thick. That's roughly two sheets of paper. Then it lifts the nozzle by that same amount and draws the next cross-section directly on top of the first.

The new layer arrives hot and melts slightly into the one below it, so the two fuse together. Repeat that a few hundred or a few thousand times and you have a solid object built up from the bed to the top.

That's what FDM stands for, more or less. Fused deposition modeling. Melted plastic, laid down, fused together.

Where the shape comes from

Someone has to tell the machine what to draw. That starts as a 3D model, either designed from scratch or downloaded from one of the big model libraries.

Software called a slicer then does exactly what the name suggests. It cuts the model into hundreds of horizontal layers and works out the path the nozzle needs to travel for each one. The printer just follows those instructions.

Three things that surprise people

It's slow. The machine is drawing your object one thin line at a time. Small parts take an hour or two. A helmet takes a day or more.

Parts aren't solid. Printing solid plastic would be slow, heavy and wasteful, so the inside is a lattice with air in it. A typical part is around 20% plastic inside, and it's still plenty strong.

Plastic can't be printed in mid-air. If part of your object overhangs with nothing underneath, the printer builds temporary scaffolding to draw on, and we remove it afterward.

Why you can see layer lines

Because they're real layers. Look closely at any printed part and you'll see fine horizontal bands up the sides.

They can be sanded, filled and painted away, and on some surfaces they read as texture and look fine as they are. But they're a normal feature of the process, not a fault.

There's another kind

Everything above describes FDM, which is what most people mean by 3D printing and what we use for the majority of jobs. There's a second process using liquid resin cured by light, which produces much finer detail on small parts. We run that too, and we have a separate article on when each one makes sense.

You don't need to know any of this

Genuinely. Send us a photo, a sketch, a broken part or a link to a model, tell us what it's for, and we'll handle the rest. The technical decisions are our job.