Design for FDM Printing: A Practical Guide
Learn how to design strong, reliable parts that print easily on FDM machines. Covers wall thickness, overhangs, tolerances, infill, and orientation — written by engineers.
1. Understanding How FDM Works
FDM prints parts one layer at a time, bonding each new layer to the one below. Parts are strongest along the X and Y axes, and weaker in the Z (build) direction between layers.
2. Wall Thickness
Use a minimum wall thickness of 1.2 mm (3 × 0.4 mm nozzle width). Thinner walls may not print reliably or may be fragile. For structural parts, 2–3 mm walls are recommended.
3. Overhangs
FDM can print overhangs up to 45° without support. Beyond 45°, support material is required. Design parts so critical faces avoid steep overhangs where possible.
4. Tolerances and Fit
For clearance fits (e.g. a pin in a hole), add 0.2–0.4 mm clearance. For press fits, test with a small sample first — tolerances vary slightly by material and geometry.
5. Infill
Infill density affects strength and weight. 15–20% is suitable for most non-structural parts. 40–60% for moderate loads. 80–100% for maximum strength (increases print time and cost).
6. Orientation
Orient parts so load-bearing features lie in the XY plane. Avoid designing parts where the critical stress direction aligns with the Z axis.
7. Holes and Fasteners
Print holes 0.2 mm undersized and drill/ream to final size for precision fits. Use heat-set inserts for threaded fasteners in plastic — direct threading into FDM is weak.
8. Large Flat Surfaces
Large flat bottom surfaces can warp during printing, especially in ABS/Nylon. Add chamfers to bottom edges or split large parts to reduce warping risk.