When 3D printed dimensions do not match the CAD model
A printed part can differ from its CAD dimensions without the entire printer being incorrectly calibrated. Outside dimensions, inside openings, round holes and the first layer can each show different behaviour. Before changing global scaling or motion calibration, identify which geometry is wrong and whether the error is repeatable.
Do not rely on one calibration cube
Test more than one feature:
- outside dimension
- internal opening
- round hole
- longer dimension
- Z height
Outside dimensions too large
Possible causes:
- over-extrusion
- elephant foot
- perimeter behaviour
- material behaviour
- slicer settings
Internal dimensions too small
Common practical causes include:
- over-extrusion
- feature geometry
- print orientation
- hole behaviour
- polygon approximation in round geometry
Global scaling is rarely the first fix
If the outside dimension is wrong, the inside feature is wrong in another way, and Z is correct, a global XYZ scale factor is not a clean solution.
Separate print error from intentional clearance
Print-process error: the printer does not reproduce the intended geometry consistently. Design clearance: two physical parts intentionally need space between them. These are different problems.
Use a test part that matches the real feature
For an end cap, a short section of the actual mating geometry is more useful than only a calibration cube.
Calculate a fit
Calculate the correct model dimension directly instead of guessing it through test prints.
Calculate a fit