The smallest hole diameter that can be printed accurately and remain open after printing, varying by technology.
Hole accuracy in additive manufacturing depends on the process resolution and material behaviour. FDM creates stair-stepped arcs: vertical holes are elliptical because layer height adds steps to the curved profile. SLA cures at the boundary of each circle: resin bleeds inward slightly, reducing effective diameter. SLS and DMLS both leave residual unfused powder inside small holes that is almost impossible to remove. Each technology requires a different compensation strategy.
FDM: always design holes 0.1–0.2 mm undersized then ream/drill to final diameter. Orient critical holes horizontally to avoid layer-step ellipse effect. SLA: holes for screws or pins should use the exact nominal diameter: bleed is often self-compensating. SLS: add a minimum 1 mm drainage slot if a blind hole is unavoidable. DMLS: specify machining tolerances after build for precision holes.
Do not assume holes will print at nominal diameter: test with a calibration print. Hole size compensation is slicer-settable in most tools but is global, not per-feature. In SLS, a 0.8 mm hole looks correct in the CAD but will be completely blocked by PA12 powder. In DMLS, thermal shrinkage during solidification reduces hole diameter by 0.1–0.3 mm.
Related terms: Minimum Wall Thickness, Minimum Printable Thread, SLS Powder-Escape Pockets
| Theme | geometry |
|---|---|
| FDM | >= 2 mm: FDM holes are printed as ellipses in vertical orientation due to layer stepping; design 0.2 mm undersized for a tight fit. Below 2 mm the hole often fully closes. |
| SLA | >= 0.5 mm: SLA achieves very fine holes down to 0.5 mm; in dental or micro-scale parts 0.3 mm is possible. Below 0.5 mm resin surface tension and viscosity block the hole. |
| SLS | >= 1 mm: SLS horizontal holes require ≥1 mm; vertical holes need ≥2 mm because trapped powder clogs smaller openings and post-process cleaning is difficult. |
| DMLS | >= 0.5 mm: DMLS laser spot allows 0.5 mm holes; 1 mm is the typical practical minimum for reliable geometry and powder clearance in metal parts. |
| Also called | minimum bore diameter, printable hole size, minimum aperture |
| Source | Wiki/tech/fdm-fff.md, Wiki/tech/sla.md, Wiki/tech/sls.md |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert