Clearance for print-in-place & assembled parts
Two surfaces that should move — a hinge, a lid, a captive nut — will fuse if you draw them touching. The trick is a deliberate gap that’s at least a nozzle-width wide.
⚡ Rule of thumb
Leave a modeled gap between any two parts that must move or assemble — start around one nozzle width and open it until they run free.
Starting point
Gap ≈ 0.4 mm (one 0.4 mm nozzle width)
Measured
Total gap between the two faces
Confidence
Process-dependent
▶ Source video — How to Design a Print with Perfect Tolerance EVERY Time — Slant 3Dwatch on YouTube ↗
Applies to
- Process
- FDM / filament
- When
- Print-in-place mechanisms, lids, hinges, captive fits
- Machine
- 0.4 mm nozzle (scale gap to your line width)
Why it matters
If two moving surfaces are modeled touching, the printer lays plastic across the gap and welds them together — the mechanism comes off the bed as one solid lump.
A gap of at least one extrusion width guarantees the slicer draws two separate walls, so the parts release from each other and move.
What good looks like
- Every moving interface has a visible gap in CAD, not a shared face
- The gap is at least one nozzle width so the slicer keeps the walls separate
- Tighter fits are dialed in from a test, not guessed
How to apply it
- Identify every pair of surfaces that must move or assemble.
- Model a gap of at least one nozzle width (≈ 0.4 mm) between them.
- For sloppy-but-free motion open it further; for a snug fit tighten toward the nozzle width.
- Print and check the joint releases and moves before scaling the design up.
Slant 3DSource & visual reference
Modeling a nozzle-width clearance between parts that must move or assemble — How to Design a Print with Perfect Tolerance EVERY Time ↗.
Summarized and independently edited by Start Here. Starting values and cautions are our editorial notes, not a quotation from the creator.