How to prepare STL and STEP files for 3D printing

Which format to send

• STEP (.step, .stp) is the best choice when you design in a CAD program (Fusion 360, SolidWorks, Onshape, FreeCAD). It carries exact geometry and units.
• STL is the universal mesh format. Export with a fine resolution (chord deviation ≤ 0.01 mm or "high" quality) so curved surfaces stay smooth.
• 3MF and OBJ are accepted too; 3MF keeps units and colours.

Models must be in millimetres. An STL has no unit information, so a model exported in inches arrives 25.4× too large – the viewer shows the bounding box so you can spot that immediately.

Wall thickness and features

Thin unsupported walls warp or break during post-processing. If a wall must be thin, add ribs or a fillet at the base.

Watertight mesh

A printable mesh is a closed surface without holes, flipped normals or self-intersections. Our viewer computes the volume and warns when the mesh is not watertight. Most CAD exports are fine; problems usually come from sculpting tools or from boolean operations that failed silently. Netfabb, Meshmixer or the "repair" function in PrusaSlicer fix the majority of cases.

Hollowing saves money

Price scales with volume (material) and, for nylon and metal, partly with surface area. A solid 50 mm cube costs many times more than the same cube with 2 mm walls. Hollow large parts and add a drain hole (≥ 3 mm) for SLA so the uncured resin can escape.

Tolerances and fits

Design snap fits and press fits with clearance: 0.2 mm for SLA, 0.3 mm for MJF/SLS, 0.4 mm for FDM. Threads below M4 should be tapped after printing or use heat-set inserts.

Orientation and supports

You do not need to add supports – the manufacturer orients the part and adds them where needed. If a surface must be cosmetic (no support marks), mention it in the note for the model.

Upload your file in the 3D printing configurator to see the dimensions, the volume and a live price per material.