FDM 3D Printing

Done When

The first layer is uniform, the walls are smooth, dimensions match the model within a couple of tenths, and the part carries its intended load.

Steps

Level the bed: a sheet of paper drags lightly under the nozzle at every corner.

Slice at 0.2 mm layers, 3 walls, 15–20 % infill; orient the part so its loads run along layers, not across.

Print the first layer slow and watch it — it should be squished slightly flat, not round.

Keep drafts off; enclose for anything above PLA.

Let it cool before removing; a warm PLA part bends.

Remove supports and deburr.

The Science

A thermoplastic softens above its glass transition and flows through a 0.4 mm nozzle at 200–250 °C; each layer must fuse to the one below before it cools, so ambient temperature, layer height and speed are a heat-transfer problem. Layers are strong along the line and weak across it — a printed part is anisotropic. Warping is differential shrinkage as the lower layers cool while the upper ones are hot.

How It Fails

Corners lifting from the bed — warping. Stringing between features from too much heat or too little retraction. Layers that split apart under load — printed the wrong way up. Under-extrusion from a partly blocked nozzle or damp filament.

Summary

Building a part layer by layer from a thread of molten plastic laid down by a moving nozzle — the machine that made rapid prototyping a household thing.