Most 3D printing problems don't start at the printer but in the file: wrong units, holes in the surface, walls that are too thin or parts drawn with no clearance. A few checks stop your part coming out too small, too weak or unusable.
STEP or STL? The formats compared
| Format | What it contains | Strength | Choose it when |
|---|---|---|---|
| STEP (.step, .stp) | Exact mathematical surfaces and units | Round shapes stay truly round | you also need CNC machining or vacuum casting, or the model may still need changes |
| STL (.stl) | A mesh of triangles, without units or colour | Universal: every 3D printing program reads it | you're only 3D printing and the model is final |
| 3MF (.3mf) | A mesh plus units, colour and multiple parts | Modern successor to STL, fewer unit mix-ups | your software supports it; check with us whether you can upload it |
| OBJ (.obj) | A mesh, optionally with texture and colour | Common for 3D scans and design or animation software | your model comes from a scan or a non-engineering program |
In short: STEP is the safest choice if your model comes from a CAD program. STL is fine for 3D printing, provided you export it properly. In Quotebase you can upload STL, STEP and OBJ.
STL export settings
Units: always millimetres
An STL file contains no units, only numbers. So model and export in millimetres. Export in inches or metres and a part arrives 25.4 times too small or 1000 times too large. Check the dimensions after uploading.
Resolution: not too coarse, not too fine
When exporting, your software turns curved faces into triangles. Too coarse and you see facets on cylinders and spheres. Too fine and the file gets needlessly heavy without a better print. Typical settings in most CAD programs:
- Chordal deviation of about 0.01 to 0.05 mm.
- Angular deviation of about 5 to 15 degrees.
- Binary STL rather than ASCII: the same model, a much smaller file.
- Pick 'fine' or 'high' in your software if it offers no numeric values.
A watertight model
A printable model is 'watertight' (manifold): its surface is fully closed, so the software knows what's inside and outside. Models from a CAD program are usually fine. Scans, digital sculpts or models built from separate surfaces go wrong more often.
- Holes in the surface or missing triangles.
- Flipped normals: faces pointing inwards instead of outwards.
- Overlapping or intersecting bodies that haven't been merged.
- Faces with no thickness, such as a loose sheet with no wall thickness.
Free programs such as Microsoft 3D Builder, PrusaSlicer or Meshmixer find these errors and often fix them automatically.
Minimum wall thickness and detail per process
How thin a wall or how small a detail can be depends on the process, the material and the size of the part. The values below are typical guide values from practice, not guarantees. Large, flat walls should be thicker; a small rib can sometimes be thinner.
| Process | Wall thickness (typical) | Smallest detail (typical) | Smallest hole (typical) |
|---|---|---|---|
| FDM | 1.2-2 mm | 0.5-1 mm | 2 mm |
| SLA | 0.6-1 mm | 0.2-0.3 mm | 0.5-1 mm |
| SLS and MJF | 1-1.5 mm | 0.5 mm | 1-1.5 mm |
Not sure whether a thin wall or fine detail will work? Upload the file to Quotebase, or email us pointing out the critical areas.
Photo: Nicole W, CC BY-SA 4.0Hollowing and drain holes
A solid model uses a lot of material. Since 3D printing is priced per cm³, it pays to hollow out large, solid parts with a constant wall thickness. The volume drops, and usually the price too.
- With SLA, liquid resin stays trapped in a cavity. Add at least two drain holes, typically a few millimetres across, preferably low down and opposite each other.
- With SLS and MJF, loose powder stays in the cavity. Add at least two holes large enough to blow the powder out, typically larger than for SLA.
- With FDM, hollowing isn't needed: the slicer already fills the inside with a pattern (infill).
Assemblies and clearances
Parts that need to fit together shouldn't be drawn at exactly zero clearance: every process has a small dimensional deviation. So leave clearance between parts. Typical guide values per side:
- Tight fit (press): typically 0.1-0.2 mm.
- Sliding or rotating fit: typically 0.2-0.4 mm, more like 0.3-0.5 mm for FDM.
- Print-in-place hinges and moving parts (SLS or MJF): typically at least 0.5 mm, so the powder can escape.
Upload each part of an assembly as a separate file, unless it's meant to be printed as one piece. That way you get a price per part and can choose quantities separately.
Checklist before you upload
- Modelled and exported in millimetres; dimensions checked.
- STEP where possible, otherwise a binary STL at fine resolution.
- Model is watertight: no holes, flipped normals or loose faces.
- Walls and details meet the typical minimums for the chosen process.
- Large solid parts are hollowed, with drain holes for SLA, SLS and MJF.
- Mating parts have clearance and each has its own file.
- The part fits the build volume. Our SLA goes up to 780 × 780 × 530 mm.