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What is 3D printing?

Starting out · 5 min read · Updated 2026-08-12

How a 3D printer turns a design on a screen into an object you can hold — explained for children, parents and teachers, with no jargon.

A 3D printer builds an object out of thin layers, one on top of the next. Most printers you will meet in a home, school or library melt a thin plastic thread and lay it down in the shape of a slice, wait for it to harden, then lay the next slice on top. Do that a few hundred times and a flat outline has become a solid thing you can pick up.

It helps to picture a loaf of bread. If you knew the exact shape of every slice, and you could stack them back up in order, you would have the loaf again. A 3D printer works from exactly that: a list of slices.

The three steps, and where a design tool sits

1. Design. You make a model — the shape you want, with real sizes. This is the part BakaroLab does.
2. Slice. A separate program cuts your model into layers and works out the path the nozzle takes. This is called a slicer, and it comes with the printer.
3. Print. The machine follows those paths. A small object takes twenty minutes; a big one can take all day.

You do not need a 3D printer to start designing. Designing, checking and saving a file all work without one. A printer is only needed for the last step — and a school, a library or an online print service can do that part for you.

Why designs are measured in millimetres

A printed object is a real object, so it has a real size, and that size has to be decided by somebody. Millimetres are the unit almost every 3D printer, slicer and design tool uses. A millimetre is about the thickness of a credit card. A common printer nozzle lays down a line about 0.4 mm wide, which is why that number turns up so often once you start reading about printing.

Getting into the habit of thinking in millimetres early is one of the most useful things a young designer can do. "Make it a bit bigger" cannot be printed. "Make it 40 mm across" can.

What a printer finds easy, and what it finds hard

• Easy: flat bottoms, thick walls, shapes that get narrower as they go up.
• Harder: thin sticking-out parts, and anything that hangs out over empty space, which needs temporary scaffolding the printer builds and you snap off.
• Impossible: floating pieces with nothing underneath them at all.

None of this is a reason to avoid ambitious shapes. It is a reason to expect the first print to teach you something, which is the whole point of printing the first one.