FDM 3D printing: how it works, costs and design rules

Fused deposition modelling melts a plastic filament and lays it down layer by layer. It is the cheapest way to make prototypes, jigs, fixtures and one-off plastic parts.

Typical tolerance

±0.2–0.5 mm

Quantities

1 to about 100

Lead time

1–5 working days

Materials

PLA, PETG, ABS, ASA, nylon, carbon-filled nylon, TPU

How it works

A heated nozzle extrudes thermoplastic along each layer path. The bed lowers after every layer. Overhangs need support structures that are removed after printing.

Benefits

• Very low cost for one-off parts.
• Complex internal shapes at no extra cost.
• Same-day turnaround in-house.

Limitations

• Visible layer lines and weaker strength between layers.
• Lower accuracy than machining.
• Overhangs over about 45° need supports.

What drives the cost

• Print time (volume, layer height and infill).
• Support material and removal.
• Engineering materials such as carbon-filled nylon.

Design rules

• Keep walls at least 1.2 mm (three nozzle widths).
• Orient the part so loads run along layers, not across them.
• Add 0.2–0.3 mm clearance for fits, or design holes undersize and drill them.
• Avoid unsupported overhangs steeper than 45° where possible.

Preparing your STEP file

• STEP keeps exact geometry; the printer software converts it. Export 3MF or STL only if the service asks.
• Use fine tessellation if you export STL so curves stay smooth.

See also the full STEP export checklist and the comparison of all processes.