Selective laser sintering (SLS) and Multi Jet Fusion (MJF) both build parts inside a bed of nylon powder, and that single fact rewrites the design rules. Loose powder supports every overhang as the part forms, so you never draw supports, and you can print interlocking assemblies in a single job. The catch is that the same powder has to get out afterward. Trapped powder, parts fused to their neighbors, and unpredictable shrinkage across a full build are the failures that actually bite. This guide covers the geometry and economics that make powder-bed parts succeed. For where powder fits against resin and filament, see our process selection guide.
No supports, but mind the powder
Because the powder cake holds everything up, overhangs, bridges, and complex organic shapes print without the support scars you fight on FDM or SLA. That freedom is the main reason to choose powder-bed for consolidated brackets, ducting, and lattice structures. The design work shifts from supporting features to making sure every internal volume can be emptied. Any hollow with no exit becomes a solid brick of loosely sintered powder that adds weight and can never be removed.
| Feature | SLS typical | MJF typical |
|---|---|---|
| Minimum wall (supported by geometry) | 0.7–1.0 mm | 0.5–0.8 mm |
| Recommended robust wall | 1.0–2.0 mm | 1.0–2.0 mm |
| Escape/de-powder hole | ≥ 3–5 mm (two per cavity) | ≥ 3–5 mm (two per cavity) |
| Clearance, moving/interlocking parts | 0.4–0.5 mm | 0.4–0.5 mm |
| Min embossed/engraved detail | ≥ 1 mm wide, ≥ 0.5 mm deep | ≥ 1 mm wide, ≥ 0.5 mm deep |
| Small pin/hole survivability | ≥ 0.8–1.0 mm | ≥ 0.5–0.8 mm |
Give every enclosed cavity at least two escape holes of 3–5 mm. One hole lets powder pack and jam; two let air flow so it flushes out.
Escape holes and hollowing for weight
Hollowing a bulky part cuts material cost and print time, and it reduces the thermal mass that drives warp. But a sealed hollow traps powder. Add at least two escape holes per cavity, positioned so compressed air and bead-blasting can chase powder through and out. Two holes matter because air needs somewhere to leave as powder exits; a single hole tends to pack and clog. Size holes generously – 3 to 5 mm minimum, larger for deep or convoluted internal channels – and place them at the lowest points of each cavity in the expected cleaning orientation.
- Long internal channels may need intermediate ports, because powder wedges in tight bends and does not flow like liquid.
- Lattice and gyroid infills self-drain far better than a single large void, and they stiffen thin sections at the same time.
- Remember that residual powder in a blind pocket will rattle for the life of the part if it is never cleared.
Clearances for interlocking and moving parts
Print-in-place hinges, captive nuts, chain links, and gearsets are a signature powder-bed capability, but only if adjacent surfaces do not fuse. Leave roughly 0.4–0.5 mm of clearance between any two surfaces meant to move or separate. Below that, heat bleed and partially sintered powder in the gap can weld the parts into one solid lump. Wider gaps are safer for large mating faces, where a thin trapped powder layer is harder to blast free. If the assembly must hit a functional fit class, cross-check our tolerances guide before finalizing gaps.
For print-in-place mechanisms, start at 0.5 mm clearance and only tighten after a test print. A fused hinge is scrap; a slightly loose one still works.
Nesting, packing density, and cost
Powder-bed economics are unlike filament or resin. You pay for the build volume and the machine time to heat it, not just the plastic in your part, so the driving metric is packing density – how many parts share one heated build. Because parts nest in full 3D with no support structures between them, a bureau will tetris dozens or hundreds of parts into one job. Design compact, nestable geometry and you ride a cheaper per-part price; design sprawling, hollow-heavy shapes that waste bed volume and each part carries more of the build cost.
This is why powder-bed shines for small-to-medium production runs of the same part: fill the bed and the fixed heating cost spreads thin. See how that plays out against other processes in our materials comparison, and note that consolidating several components into one printed part removes assembly labor on top of the per-part savings.
Dimensional spread and finishing
Nylon shrinks as it cools from the sinter temperature, and the cooldown is not perfectly uniform across a densely packed bed. Parts near the edges cool differently from parts buried in the center, so identical geometries can vary slightly depending on where they land in the build. Expect a realistic tolerance band on the order of ±0.3 mm or ±0.3% for larger dimensions, and treat any tighter requirement as a machining or reaming operation after printing. Orient critical dimensions thoughtfully and flag them to your bureau so they can position and compensate.
Raw SLS and MJF parts come out matte and slightly porous. The standard finish is bead blasting, and the standard color step is vat dyeing, which reaches only a shallow depth – a scratch or a later machining pass exposes the natural gray or off-white core. MJF parts have a characteristic gray base tone that dyes deep and even to black; lighter custom colors read more consistently on SLS's paler powder. Design around dye depth: do not rely on color for a surface you plan to machine.
Powder-bed design rewards practice with nesting and clearances. Foundations covers the fundamentals free, and the Pro tracks dig into production-run economics.
Take Foundations free See Pro pricingPre-print checklist
- Confirm walls meet the process minimum – roughly 0.7–1 mm for SLS, 0.5–0.8 mm for MJF – and thicken to 1–2 mm where robustness matters.
- Add at least two escape holes (3–5 mm) to every enclosed cavity and prefer lattice infill over large sealed voids.
- Set 0.4–0.5 mm clearance on all moving or interlocking surfaces, then verify with a test print.
- Design compact, nestable geometry to raise packing density and lower per-part cost.
- Budget ±0.3 mm / ±0.3% dimensional spread; plan post-machining for tighter fits.
- Account for shallow dye depth – do not rely on color on surfaces you will machine.