What tolerances can I realistically expect from SLS nylon (PA12)?

Question

I'm designing a snap fit housing to be printed in SLS PA12 . The datasheet says ±0.3% with a lower limit of ±0.3 mm, but I've heard shrinkage varies a lot with part orientation and packing density. Part size: ~120 × 80 × 40 mm Critical feature: 2 mm snap fit beams and a 4.2 mm bore for a press fit pin What should I design for, and should I leave the bore undersized and ream after printing?

Selin Demir · Accepted Answer

Design for ±0.25 mm on features under 50 mm and ±0.3% above that, and you'll be safe with any decent bureau. For the bore: yes — print it at 4.0 mm and ream to 4.2 H7. Powder bed holes under 5 mm always come in slightly small because of thermal bleed. Snap fit beams at 2 mm are fine; keep the root radius ≥ 0.5 mm so the layer boundary isn't a stress riser. Orientation: ask for the part to be nested with the bore axis vertical Z . Round holes stay rounder that way.

Lukas Novak · Answer

Adding to Selin's answer: PA12 also absorbs moisture ~0.5–1% , so measure critical features after 48 h at room humidity, not straight out of the depowdering station.

Marcus Weber · Answer

Great, thanks both. Printed a test coupon with the bore at 4.0 mm, reamed to 4.2 — perfect press fit.

What tolerances can I realistically expect from SLS nylon (PA12)?

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