What is FDM 3D printing, and when is it the right choice?

Fused deposition modeling (FDM) is a 3D printing process that melts plastic filament and lays it down one thin layer at a time, and it is the lowest-cost way to make a real plastic part. It is the right choice for prototypes, jigs, enclosures and big models, and the wrong one when you need very fine detail, a smooth surface straight off the printer or equal strength in every direction.

FDM (filament printing) at a glance

Normal-size part: about 10 to 15 cm across. Larger prints take longer, so check with us.

Design figures come from our 3D printing design rules, which set filament beside resin, nylon and metal.

Know it should be filament? Upload your file for an instant price

How FDM works: a hot nozzle draws one layer at a time

Software called a slicer cuts your 3D model into thin layers, 0.1 to 0.3 mm each. The printer pushes plastic filament through a heated nozzle and traces the first layer on the build plate, then rises one layer and draws the next on top, where it fuses to the one below.

• Inside the part: the walls are solid, and the inside is a lighter grid called infill, so a part uses less plastic than a solid block.
• Other names: fused filament fabrication (FFF) and filament printing are the same process. The standard files it under material extrusion, one of seven families of additive manufacturing.
• Mid-print pauses: because the part is open while it builds, nuts and magnets can be dropped in and sealed by the next layers (embedding hardware).

See what we print in our studio

Layer lines and strength: weaker across the layers

Every FDM part shows fine lines where one layer meets the next. Up close they are easy to see, and they catch the light on a curved face.

• Strength: a layer is only fused to the one below, so a part is weaker across its layers. Carbon-fibre nylon (PA6-CF) pulls apart at 102 MPa along its layers but 48 MPa across them, according to its maker’s data sheet.
• What we do about it: we turn a loaded part on the printer so the load runs along the layers. Tell us in the notes how the part is loaded.
• A smooth surface: the lines are filled and sanded, then a primer goes on before the paint (colour and finishing).

See how layer direction decides if a part holds

Supports: needed under anything leaning past 45 degrees

A layer can only be drawn on something. A face that leans out more than 45 degrees from vertical needs supports under it: thin printed scaffolding that is snapped off after printing.

• The cost of supports: they leave rough marks where they touch, which are sanded smooth if the face shows.
• Designing them out: a chamfer of 45 degrees under a ledge prints itself, and a short gap of under about 10 mm in PLA bridges cleanly with nothing under it.

Check your design against the filament rules

Materials: PLA for most parts, carbon fibre for tough ones

PLA is the usual choice for models and display pieces. PETG suits working parts, ABS copes with warm places, ASA stands up to the sun and TPU is for parts that bend (PLA, PETG, ABS, ASA or TPU). For jigs, fixtures and end-use parts, carbon-fibre and engineering filaments such as PETG-CF, PC and PA6-CF go stiffer and hotter (engineering filaments). Other brands or special filaments are on request.

Upload your file and compare filaments for your part

Size: up to 1 m x 1 m x 1.2 m in one piece

One FDM piece can be up to 1000 x 1000 x 1200 mm on our large-format printer, and about a 360 mm cube on the desktop printers. Anything bigger is printed in sections with pegs that line them up, then glued or bolted together (how big a 3D print can be).

Big part? Upload it and we suggest where to split it

Detail: fine enough for 0.6 mm features and 1.0 mm text

The finest raised or recessed detail that prints in filament is 0.6 mm. Lettering needs strokes of 1.0 mm and letters at least 5 mm tall to read at arm’s length.

• Accuracy: ±0.3 mm on parts up to 100 mm, then ±0.3%. Holes print slightly small, so a hole that must fit is drilled or reamed (3D print tolerances).
• Finer than that: resin printing holds 0.5 mm detail and 2 mm letters, with a smoother surface.

Part that must fit something? Tell us the fit

Colours: up to four in one print

One FDM print can carry up to four colours: the printer swaps filaments as it builds, so the colour runs right through the plastic and cannot chip off. We stock about 30 solid PLA colours. For an exact brand colour, or more colours than one print holds, the part is primed and painted (choosing colours).

Pick up to four colours in your quote

Lead time: 4 to 7 working days for a normal-size part

A part about 10 to 15 cm across takes 4 to 7 working days from a confirmed quote. Express is 3 to 5 working days and Super Rush 1 to 3. Larger prints take longer, so check with us, and a part that is primed and painted takes 12 to 18 working days (how long an order takes).

Working to a date? Tell us your deadline

When another process suits better: resin, nylon, CNC or a mould

• Resin printing (stereolithography, SLA): for fine detail and a smooth surface to paint or plate, such as figurines and small display pieces. It is more brittle. See resin printing.
• Nylon powder (selective laser sintering, SLS, or Multi Jet Fusion, MJF): for tough clips, hinges and housings that are equally strong in every direction, with no supports. See SLS and MJF.
• CNC machining: for metal or plastic faces held tighter than ±0.3 mm, or a simple solid shape. See CNC machining.
• Moulding: past about 20 identical parts, silicone moulding is often better value, and past about 1,000, injection moulding (printing or moulding).

Our FDM, SLA or SLS guide compares all five printing processes side by side.

Not sure which process? Tell us what the part has to do