For moving parts in SLS: 0.3-0.5 mm clearance. Enough to absorb SLS tolerance and let the part move smoothly after de-powdering. Precision fits (press-fits, guides, precision hinges): 0.2 mm possible with careful design. Print-in-place mechanisms (single-print hinges, ratchets): 0.5 mm works better.
Why you need clearance
SLS has ±0.1-0.3 mm dimensional tolerance. If you design an assembly where part A fits inside part B (both printed), total deviation can reach 0.4-0.6 mm. Without clearance the parts do not fit.
SLS surfaces have a light grain (Ra 10-15 µm) that adds friction on tight fits. And de-powdering (clearing loose powder) needs visible clearance to get the powder out.
Clearance per application
Hinges to assemble after printing – 0.3-0.4 mm in the pin hole.
Press-fits with light hand force – 0.2 mm undersize on the shaft, if carefully designed and post-processing considered.
Guides where a part slides – 0.3-0.5 mm for smooth motion without rattle.
Bolt or screw holes – 0.3-0.5 mm larger than the bolt diameter.
Print-in-place mechanisms (e.g. gears as one piece) – 0.5 mm minimum plus a large outflow opening.
Where you can push more or less
Prototype iterations: start generous (0.5 mm), tighten in later versions. Parts after CNC finishing: tight H7/g6 fits are achievable if you mark the fit surfaces as “oversize”.
Parts without post-processing: 0.3 mm is a safe standard for most applications. Our engineers gladly look during the DfAM check whether your tolerances are realistic for the intended function.