How to prepare a model for 3D printing: formats, wall thickness, orientation and tolerances
What to do with a 3D model before printing so the part is cheaper, stronger and accurate first time. File formats, minimum thicknesses, overhangs, orientation, tolerances and finishing.
Most 3D printing problems do not start on the printer. They start in a model that was never prepared for printing: a wall thinner than the nozzle can lay down, a hole designed at nominal size with no clearance, an overhang with nothing under it. This is what we check on every file that reaches us, and what you can do yourself so the quote comes in lower and the first part is usable straight away.
Which files should you send?
- STL is the most common format and is enough for most parts. Export at a fine resolution (deviation 0.01 mm, angle 5°), otherwise curved surfaces come out visibly faceted.
- STEP is better for us when we will edit the model or check dimensions. It keeps exact geometry and units.
- 3MF carries units and colours along with the geometry and never has scale problems.
- OBJ is accepted, but without textures it adds nothing over STL.
Check the units before you send. A model in inches instead of millimetres is the most common reason a part arrives 25 times smaller than intended. If in doubt, put one reference dimension in the message, for example the overall length.
How thin can walls and details be?
Every technology has a limit below which a feature will not form or will be fragile.
| Feature | FDM (0.4 mm nozzle) | SLA resin |
|---|---|---|
| Load-bearing wall | from 1.2 mm, ideally 1.6 to 2 mm | from 1.0 mm |
| Non-structural wall, cover | from 0.8 mm | from 0.6 mm |
| Embossed text, logo | letter height from 5 mm, depth 0.6 mm | letter height from 2.5 mm, depth 0.3 mm |
| Free-standing pin | diameter from 3 mm | diameter from 1.5 mm |
| Hole | diameter from 2 mm | diameter from 0.8 mm |
Design walls as multiples of the extrusion width. With a 0.4 mm nozzle that means 0.8, 1.2, 1.6 or 2.0 mm. A 1.0 mm wall prints worse than a 1.2 mm wall even though it is thinner.
How do overhangs, bridges and supports affect the print?
FDM builds layer on layer, so every layer needs something beneath it.
- Overhangs up to 45° print without supports. Above that, supports are needed and the surface under them will be rougher.
- Horizontal bridges up to 20 to 30 mm work without supports. Longer ones sag.
- A 45° chamfer instead of a flat edge above a cavity often removes supports entirely. The part is cheaper and cleaner.
- On SLA, supports are part of every print but leave small marks. If one face has to be the visible one, say so in the message and we orient it away from the supports.
Why does orientation decide strength and price?
An FDM part is weakest between layers. A clip or hook printed lying flat survives several times more bends than the same part printed standing up. Think about where the load goes when you design, and tell us. We choose the orientation so that:
- the main load runs along the layers, not across them,
- the visible face is on top or on the side, never on the bed or above supports,
- support volume and print time, which make up most of the price, are minimised.
When these three pull in different directions we come back to you with a proposal, for example splitting the part in two with a glued or bolted joint.
What clearances and tolerances should you design in?
Typical FDM accuracy is ±0.2 mm over the first 100 mm. SLA holds ±0.1 mm. Holes come out slightly smaller than modelled, outside dimensions slightly larger.
- Clearance hole for an M4 screw: model it at 4.3 to 4.5 mm.
- Hole for a pin that should hold by friction: pin diameter plus 0.1 mm.
- Hole for a freely rotating shaft: plus 0.3 to 0.4 mm.
- Snap fits: 0.2 to 0.3 mm clearance per side.
- Heat-set threaded inserts: hole to the insert maker’s data, usually 0.2 mm smaller than the insert’s outer diameter.
If you need a tighter fit we drill or ream the hole after printing. Put it in the request and we include it in the quote.
What else should you check before sending?
- The model is closed (watertight), with no holes in the mesh and no flipped faces. Most CAD packages have a “check mesh” tool.
- No duplicate or overlapping bodies. Merge them into one.
- Replace sharp internal corners with a 0.5 to 1 mm fillet. It reduces stress and cracking.
- A large flat base in ASA or nylon can warp on FDM. Rounded edges and splitting the area help.
- Text and logos: raised text is safer than recessed text.
What surface finish can you expect?
Layers are visible on FDM. At 0.2 mm layer height you can feel them, at 0.12 mm only on sloped faces. SLA gives a smooth surface with no visible layers. If the part goes to a customer or onto a reception desk, consider sanding and painting, or printing it in resin. The materials overview covers each material’s properties and the pricing page gives indicative prices.
In short
Send a STEP or a finely exported STL in millimetres, keep walls at multiples of 0.4 mm, keep overhangs under 45°, add clearance to holes and tell us which face is visible and where the load goes. The rest (orientation, supports and print settings) is our job. If you do not have a model, we build it from a sketch or a sample.