How to Design for 3D Printing: Tolerances, Walls & Overhangs

A well-designed file prints right the first time. A poorly designed one costs you time, money, and a reprint. These are the rules we apply to every job that comes through Layer One.

01 Minimum Wall Thickness

Thin walls collapse during printing or snap in post-processing. For FDM, keep walls at least 1.2 mm (two extrusion widths). For resin (SLA/DLP), you can go as thin as 0.8 mm, but 1.0 mm+ is far safer.

02 Overhangs & Support Angles

FDM printers can bridge unsupported angles up to about 45° from vertical without supports. Beyond that, the plastic droops. Design chamfers instead of horizontal overhangs wherever possible — it saves support removal time and leaves a cleaner surface.

03 Hole Sizing & Fit Tolerances

Printed holes always come out slightly smaller than modelled due to material shrinkage and layer stacking. Add 0.2 mm to holes that need to accept a shaft or bolt. For press-fit parts, reduce that to 0.1 mm.

04 File Format & Export Settings

We accept STL, OBJ, and STEP files. STEP is preferred for mechanical parts because it preserves exact geometry — STL approximates curved surfaces with triangles, which can introduce small errors at tight tolerances.

• STL resolution: Export at 0.01 mm chord deviation / 0.5° angle — higher than this inflates file size with no print benefit
• Units: Always export in millimetres. We receive files in inches occasionally and the scale errors are painful
• Watertight mesh: Ensure your model is a closed, manifold solid — no holes in the surface geometry

05 Orientation Matters

The direction a part is printed affects its strength. FDM parts are weakest along the Z-axis (layer lines). If your part will experience bending stress, orient it so the load runs parallel to the print bed, not perpendicular to it.