The design guideline that unsupported overhanging surfaces should not exceed 45° from vertical (or 45° from horizontal for bridges) to print without support structures.
FDM layers must deposit on a surface ≥ 50% supported by the layer below. At 45°, each layer shifts by one extrusion width: borderline supported. Beyond 45°, drooping occurs. Bridge length (horizontal span between supports) limit: typically 30–60 mm for PLA at 0.2 mm layers depending on cooling.
Redesign parts to eliminate overhangs: (1) chamfer 45° instead of horizontal bottom faces, (2) split and bond for complex overhangs, (3) reorient in build space. When supports are unavoidable, design support interfaces (0.2 mm gap) for clean removal. Use tree supports for organic shapes.
The 45° rule is material and machine dependent. Fast print speeds and poor cooling degrade overhang quality. Heated chambers (ABS/ASA) reduce cooling and worsen overhangs. Always test critical overhangs on the target machine with target settings before finalizing design.
Related terms: DfAM (Design for Additive Manufacturing), Build Orientation, Minimum Feature Size, Draft for Assembly
| Field | engineering |
|---|---|
| Also called | 45-degree rule, self-supporting angle, overhang angle |
| Source | EDi Brain: rules-core |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert