We print with FDM (fused deposition modelling): the printer melts a plastic filament and lays it down as thin lines, one flat layer at a time, from the build plate upwards. Almost every design rule follows from that. Each layer has to rest on the layer below it, and the bond between two layers is weaker than the plastic inside a layer.

Overhangs

An overhang is any part of your model that leans out over the layer below it. Every new layer can stick out a little beyond the previous one, so gentle slopes print without help. As a rule, anything up to 45° from vertical prints cleanly. Steeper than that, the edge of each layer hangs in the air, sags and curls up.

Steeper overhangs need support : a temporary structure printed underneath that holds the overhang up and breaks away afterwards. Support costs extra material and time, and it leaves a rougher surface where it touched your part. Parts that need supports are shipped with the supports still attached, so you can remove them yourself; flush cutters and small pliers work best.

Ways to need less support:

• Use chamfers on bottom edges instead of rounded fillets. A 45° chamfer prints by itself; the bottom half of a fillet is a steep overhang. Fillets on top and side edges are fine.
• Bridges are fine when they are short. A flat span between two supports (the top of a doorway shape) prints in mid-air up to about 10 mm with a clean underside. Longer spans start to sag.
• Make horizontal holes teardrop shaped. A round hole lying on its side has a flat overhang at the top. Up to about 8 mm across it prints acceptably; above that, give the top a 45° point (a teardrop) and it prints cleanly.
• Think about orientation. Lay your part on its largest flat face. You choose the shape, we place it on the plate, so design a flat side where you can.
• Split large or complex parts. Two simple halves glued or screwed together often print better, stronger and cheaper than one part full of support.

Layer lines

Because a print is built from stacked layers, it is not equally strong in every direction. Along the layers, the plastic is one continuous line and it is strong. Between the layers, it is only fused to the layer below, so a part pulled or bent so that the layers separate breaks much more easily, often at half the strength or less.

• Design so the load runs along the layers. A hook or bracket printed lying flat is far stronger than the same part printed standing up, where it snaps along a layer line.
• Layer lines show on sides and slopes. Vertical walls show a fine horizontal texture. Shallow slopes and domes show steps (see Layer). Flat tops and the bottom face, which sits on our textured plate, are smoothest.
• Tall, thin features are weak. A thin pin standing upright can snap off between two layers. Make it thicker, add a fillet where it meets the body, or lay it down.

Walls, details and text

• Minimum wall thickness: 0.8 mm (two printed lines). Use 1.2 mm or more for anything that has to carry load.
• Smallest detail: about 0.4 mm across, the width of one printed line. Anything finer disappears.
• Text: letters at least 5 mm tall, with strokes at least 0.5 mm wide and 0.6 mm raised or deep. Text on a top face or a vertical wall reads best.
• Bottom edges: the first layer is pressed onto the plate and comes out slightly wider (the "elephant’s foot"). If the bottom edge has to fit into something, add a small 0.3 to 0.5 mm chamfer there.
• Large flat parts in ABS and ASA can warp at the corners as they cool. Rounded corners and a bit of thickness help.

Your file

• Upload STL, STEP or 3MF, up to 100 MB per file. STEP keeps curves exact, so it is a good choice from CAD software.
• Model in millimetres. We print the file at the size it is in; check the size the Instant quote shows for each model.
• The largest part we can print is 256 × 256 × 256 mm.
• Make sure the model is closed (watertight) and is one solid body per part. Most CAD programs do this by default; scans and game models sometimes need repair first.

A tolerance is how far a printed size may differ from the size in your model. On our printer you can expect most dimensions within about ±0.2 mm. Large parts and parts in ABS and ASA, which shrink a little as they cool, can be slightly further off. If a measurement is more than 0.5 mm off your model, we count the print as faulty and fix it (see Returns and refunds).

Parts that fit together

When two printed parts, or a printed part and a bought part, have to fit together, leave a gap between them in your model. Both surfaces come out a little rough and a little off size, so a 10 mm peg in a 10 mm hole will not go in. The gap below is the space on each side, so a 10 mm peg with a sliding fit needs a 10.4 mm hole.

Holes and threads

• Holes come out slightly smaller than modelled, especially small ones. For a screw to pass through, make the hole 0.2 to 0.4 mm bigger than the screw, or drill it out afterwards.
• Vertical holes (pointing up from the plate) are round and accurate. Horizontal holes are less round at the top; see the teardrop tip above.
• Threads: printed threads work from about M6 upwards. For smaller screws, model a pilot hole and use self-tapping screws, or press in brass heat-set inserts yourself (model the hole to the insert maker’s size).

Layer height is the thickness of each printed layer. It mostly changes how a part looks, and how long it takes to print. You can choose it under Advanced on the Instant quote page; Basic always prints at 0.20 mm.

Print time is a large part of the price, so thinner layers cost more. Some things to keep in mind:

• Layer height only affects the up direction. Detail on a flat top or in the outline seen from above depends on the nozzle, not on the layer height.
• Heights snap to layers. At 0.28 mm a 10 mm tall feature becomes 10.08 mm or 9.80 mm. If heights must be exact, use a thinner layer or design to a multiple of the layer height.
• Thinner is not stronger. Parts at 0.20 or 0.28 mm are usually as strong or stronger than at 0.08 mm. Choose fine layers for looks, not for strength.

The nozzle is the opening the melted plastic comes out of, and its size sets the width of every printed line. We print every order with a 0.4 mm nozzle, the standard size and the best balance between detail and speed. It lays lines about 0.4 to 0.45 mm wide.

What that means for your design:

• Design walls in steps of about 0.4 mm: 0.8, 1.2, 1.6 mm and so on. A wall of 1.0 mm still prints, but the printer has to fill the leftover space with a thin extra line, which is less neat.
• Features thinner than 0.4 mm can’t be printed. Fine ridges, thin text strokes and sharp inside corners get rounded to the line width.
• Sharp inside corners seen from above come out with a tiny radius of about 0.2 mm. Design a small corner radius where parts have to fit in.

If your project really needs a different nozzle, email us before you order and we will tell you what is possible.

A print is not solid plastic. It has a solid outer skin, the walls on the sides and solid layers on top and bottom, and a light pattern inside called infill . How strong a part is depends mostly on its walls, its orientation and its material, and much less on infill.

Basic: choose a strength

Advanced: what each setting does

• Wall loops (1–6): the number of lines around the outside. This has the biggest effect on strength, especially for bending and for screw holes. Going from 2 to 4 walls helps more than going from 20% to 50% infill.
• Infill density (10–100%): how full the inside is. 15 to 25% is plenty for most parts. Above 50% the part gets heavy and expensive for a small gain. 100% makes a solid part.
• Infill pattern: gyroid is equally strong in all directions and a good choice for strong parts; grid and lines are fast and fine for light parts; cubic, triangles and honeycomb are stiff, solid choices in between.
• Support type: Normal suits flat overhangs, Tree touches less of the surface and suits rounded and organic shapes. Choose None only if your part has no overhangs steeper than 45°.

Design tips for strength

• Orient for the load: make sure the force runs along the layers, not across them (see Layer lines).
• Add fillets to inside corners. A sharp inside corner concentrates stress and cracks first; a 1 to 2 mm radius spreads it.
• Make it thicker where it matters instead of filling the whole part. Thicker walls around holes and at mounting points add a lot of strength for little material.
• Pick the right material. PLA is stiff but snaps; PETG bends before it breaks; ABS and ASA handle heat. See Materials.

We print in six materials. The Instant quote page shows only the materials and colours we have in stock right now, so not every material below may be available on the day you order.

Quick picker

Softening temperatures are typical values for these materials, not guarantees. A part under load softens earlier.

1. Export your model as STL, STEP or 3MF, in millimetres.
2. Upload it on the Instant quote. You can add up to 12 models at once and turn each one around in 3D to check it.
3. Choose your settings for each model: amount, material, colour and strength under Basic, or layer height, walls, infill, pattern and supports under Advanced. “Copy to all models” applies one model’s settings to the rest.
4. Get your price in seconds, then add everything to your cart and check out.
5. We print and ship it. Until printing starts you can cancel for free from My account.

What decides the price

• Material: how much plastic your part uses, including walls, infill and any support, and which material it is.
• Print time: bigger parts, thinner layers and more walls and infill take longer.
• Setup: each build plate has a small setup cost. Parts with the same material, colour and layer height that fit on one plate share it, so ordering several parts at once is cheaper.