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Dimensional accuracy

3D printing tolerances: plan fits, holes and threads

CAD dimensions are not automatically part dimensions. Tolerances depend on process, material, orientation, size and post-processing.

Accuracy8 min

Summary

Key points

  • Resolution is not the same as accuracy.
  • FDM holes often need allowance or drilling.
  • Threads and inserts should be designed deliberately.
  • Test coupons are cheaper than failed assemblies.

Separate resolution and tolerance

Resolution is not the same as accuracy.

Translate the requirement into a measurable target before selecting a process or profile.

FDM tolerances

FDM holes often need allowance or drilling.

Check geometry, material and orientation together instead of optimizing one setting in isolation.

SLA and SLS limits

Threads and inserts should be designed deliberately.

Document the practical limit that would make the part unusable in its real environment.

Holes and threads

Test coupons are cheaper than failed assemblies.

Use a representative test feature when fit, load or surface quality is critical.

Test coupons

Resolution is not the same as accuracy.

Record the confirmed model revision and production assumptions for repeat orders.

FAQ

Common questions

Why are printed holes often too small?

Material flow, line width and circular approximation can shrink inner contours. Critical holes need clearance or drilling.

Should I order a test piece?

For tight fits, high load or repeated orders, a small test coupon is usually cheaper than a complete failed part.

Sources

Studies and technical sources