Openings or channels in SLS hollow parts that allow unfused powder to escape after sintering, preventing trapped powder pockets.
SLS prints are surrounded and supported by unfused powder, which is recycled after printing. Any sealed internal volume, hollow body, internal channel closed at both ends, traps this powder permanently. The trapped powder cannot be removed without destroying the part. Unlike SLA drainage holes, SLS powder-escape is about weight, rattle, and hygroscopicity: PA12 powder absorbs moisture which can cause internal stress over time. The powder is also expensive to lose.
Design every hollow section with at least one escape hole ≥3.5 mm in diameter. For complex internal geometries, use two holes at opposite ends to allow air-blast cleaning. If aesthetic or functional constraints prevent holes on the final part, plan a plugging operation post-cleaning. Lattice infill structures (rather than fully hollow shells) are often a better alternative: they allow powder to escape through the lattice openings.
A 3 mm hole sounds large but PA12 fine powder is cohesive: it needs vibration and air pressure to exit, not just gravity. Holes under 3 mm often leave a caked residue. Horizontal circular holes are partially blocked by sintered walls: elongated slots are more effective. Do not rely on thin walls flexing to dislodge powder: PA12 is stiff.
Related terms: SLA Drainage Holes for Hollow Parts, Minimum Hole Diameter, Minimum Wall Thickness
| Theme | geometry |
|---|---|
| SLS | None None None: Avoid sealed hollow cavities: trapped unfused powder adds weight, rattles, and cannot be removed. Add powder-escape holes (≥3.5 mm) at the lowest accessible point of any enclosed volume. |
| Also called | powder drainage, powder trap avoidance, powder clearance hole |
| Source | Wiki/tech/sls.md, Wiki/materials/nylon-pa.md |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert