SLS Accuracy Starts With Process Reality
SLS can produce accurate functional parts, but it is not dimensionally perfect. Powder behavior, laser path, heat, shrinkage compensation, cooldown, part size, and finishing all influence the final measurement. Accuracy is a workflow outcome, not just a printer specification.
SLS Accuracy Starts With Process Reality
SLS can produce accurate functional parts, but it is not dimensionally perfect. Powder behavior, laser path, heat, shrinkage compensation, cooldown, part size, and finishing all influence the final measurement. Accuracy is a workflow outcome, not just a printer specification.
Tolerances matter most where parts fit together: holes, slots, pins, bosses, snap fits, gears, hinges, and mating faces. A decorative surface can accept more variation than a bearing seat or sealed interface.
Design Rules and Minimum Features
Formlabs’ Fuse design specifications list very small minimum supported and unsupported wall values for its system, but minimum printable does not mean best functional design. A wall that prints may still be too weak, too flexible, or too easy to damage during cleaning.
Use supplier design guides as the floor, then add margin for the actual use. A production clip, tool, or enclosure deserves more conservative geometry than a visual sample.
Clearance for Assemblies
Moving parts and fitted features need practical clearance. Powder must leave the gap, surfaces may be blasted or dyed, and nylon can have a textured finish. If two parts are modeled with zero clearance, they may bind or fuse.
For important joints, print tolerance coupons with several gaps. Test 0.2 mm, 0.3 mm, 0.5 mm, and larger clearances if the supplier recommends them. The right value depends on material, machine, finish, and part scale.
Holes, Pins, and Fasteners
Small holes may close, shrink, or retain powder. Long narrow holes are harder to clean than shallow holes. For critical fastener holes, designers often undersize or oversize strategically and then drill, tap, ream, or insert hardware after printing.
Bosses around screws need enough wall thickness and fillets to avoid cracking. Heat-set inserts, press-fit inserts, or captured nuts can improve repeated assembly when raw nylon threads are not suitable.
Part Size and Warping
Large flat parts are more likely to warp than compact rounded parts. Broad plates, uneven wall sections, and thick blocks hold heat differently across the build. That can affect flatness even when small features measure well.
Add ribs, radii, relief features, or split the design when flatness is critical. If a surface must be precise, leave machining allowance for post-processing rather than expecting raw SLS texture to serve as a finished datum.
Finishing Changes Measurements
Media blasting, tumbling, dyeing, sealing, and vapor smoothing can all affect surface feel and dimensions. Tumbling removes material gradually. Coatings can add thickness. Dyeing may not change much dimensionally, but it is still part of the finished-part workflow.
Measure parts after the intended finish. A raw sample is useful, but it may not represent the final product that reaches the customer.
Tolerance Checklist
Define critical dimensions before ordering. Add clearance tests, choose conservative wall thickness, avoid long narrow powder traps, and use post-machining for truly tight interfaces. Keep supplier, material, orientation, and finish consistent across batches.
SLS accuracy is very useful when the design respects the process. It becomes frustrating when CAD dimensions are treated as guaranteed physical dimensions.
FAQ
How accurate is SLS 3D printing?
SLS can be accurate enough for many functional parts, but final tolerance depends on material, machine, geometry, finish, and supplier workflow.
Do SLS holes need extra clearance?
Often yes. Small holes and fitted features should be tested, cleaned, or post-machined when fit matters.
Does finishing affect SLS tolerances?
Yes. Tumbling, blasting, coating, dyeing, and vapor smoothing can affect surface and fit, so measure after the final finish.
