How to spot it

The same stand drawn see-through, with the lines where parts cross in black
See-through: black lines are where the parts cross.
  • Bambu StudioNo warning for a peg joined into a block; volume shown 11,166 mm³ instead of 10,853Tested: Bambu Studio 2.8 on macOS, tested 2026-10-27
  • Bambu StudioNo warning for a boolean cutter left in the file; it printed as a solid cylinderTested: Bambu Studio 2.8 on macOS, tested 2026-10-27
  • UltiMaker CuraUnion Overlapping Volumes "may cause unintended internal cavities to disappear"Cura 5.13 definitions

Why it happens

  • Parts joined without a boolean union
  • A hidden boolean cutter exported with the model
  • Kits and assemblies saved as one file

In our tests

12/ 198

12 of the 198 public test files had overlapping parts. FixSTL reported them and left them in place in all 12.

FixSTL reports these and leaves them: merging parts changes the design, so it is your call.

Public Thingi10K test set, FixSTL engine 0.6.0 (a7ea280), default repair. How we test

How to fix it

What FixSTL does

  • Reports overlapping parts and points to a boolean union

What it leaves

  • Merging or splitting parts along the line where they cross
  • The check runs on files up to 1,000,000 triangles and sees the first 32 crossing pairs

Elsewhere

  • Blender Boolean modifier, Union: one part, no crossings
  • Blender export Disable a cutter in renders, or export with Selection Only
Check your STL