3D Printing Tolerances and Accuracy: What to Expect

The Numbers That Matter

Every manufacturing process has a tolerance envelope, and designing without knowing it produces parts that don't fit. For professional 3D printing, the standard envelopes are +/- 0.2mm for FDM and +/- 0.1mm for SLA (or +/- 0.2% on dimensions above 100mm, whichever is greater). Those numbers are achievable on every order without special requests — tighter is possible on specific critical dimensions when flagged in advance.

Where Deviation Comes From

Understanding the sources helps you design around them:

• Thermal shrinkage: thermoplastics contract as they cool; slicers compensate, but tall/large parts accumulate more variance than small ones.
• Layer quantization: vertical dimensions round to the nearest layer height — a 10.05mm height printed at 0.2mm layers lands on 10.0 or 10.2.
• Hole shrinkage: FDM holes print 0.1-0.3mm undersize because the extrusion path bulges inward on curves. Design holes oversize or drill/ream them.
• Overhang sag and support scarring add local deviation on downward-facing surfaces.
• SLA post-cure shrinkage is small and uniform, which is why SLA holds tighter tolerances overall.

Design Guidelines for Parts That Fit

The clearances that work, learned from thousands of mating parts:

Surface Finish Expectations

FDM surfaces show layer lines of 0.1-0.3mm pitch; visually smooth after light sanding, and top surfaces near-flat. Vertical walls measure roughly Ra 6-12 um depending on layer height. SLA surfaces measure Ra 1-3 um — effectively injection-mold class — with layer structure invisible at normal viewing distance. If a gasket or seal face needs better than printed finish, call it out: a two-minute facing pass or a switch to SLA usually solves it.

How to Ask for Tighter

When one or two dimensions genuinely need better than the standard envelope, the answer is rarely a different process — it's communication. Note the critical dimensions in your order (a marked-up screenshot or drawing works). We orient the part so those dimensions land in the accurate plane, adjust compensation, and verify with calipers before shipping. Sub-0.1mm bores get reamed; critical threads get real taps. That workflow covers most precision requests without CNC pricing.

Check Your Part in Seconds

Upload your model, and the quote reflects the geometry automatically. If tolerances are the deciding factor between FDM and SLA for your part, quote both and compare — and put the critical dimensions in the notes so our team can confirm feasibility before anything prints.