SLS parts are dimensionally stable within ±0.15 mm up to 100 mm, and keep their size long-term. Provided they are not exposed to extreme temperature (>80 °C continuous) or chemical aggression. Water absorption on PA12 and PA 950 HD can give 0.5-1% dimensional change. For dry indoor use not noticeable, for humid environments sometimes.
What we mean by "dimensionally stable"
Two aspects: initial dimension after print (how close to CAD) and dimension over time (does it stay stable?).
Initial dimension – Our SLS parts hit ±0.15 mm on dimensions up to 100 mm at standard orientation.
Long-term stability – PA12 and PA 950 HD stay within ±0.1% of the original dimension for years under normal indoor conditions (dry, <=40 °C). Carbon LW is even more stable thanks to fibre reinforcement. PA11 has slightly lower water absorption and stays more stable in humid environments.
Where dimensional stability can drop
High humidity. Nylons absorb water (PA12 ~1%, PA11 ~1.5%) and expand a little. For outdoor applications or humid industrial environments: PA11 has the lowest absorption.
Extreme temperature. Continuous >80 °C softens PA12. For hot applications: PA802CF (HDT 179 °C) or other fibre-reinforced materials.
UV exposure. Outdoor and direct sun discolour PA materials and can affect mechanical properties over years. For outdoor: consider UV stabilisation or a coating.
Practical advice for sensitive applications
Design for tolerance recovery: model a small manipulator surface (0.3-0.5 mm) on one side of critical dimensions so post-milling is possible.
For fit-critical parts: prototype test at expected temperature and humidity.
For long-term stability: Carbon LW or PA802CF offer the best dimensional stability through fibre reinforcement. Our engineers gladly work out which material is optimal for your specific environment.