What we tested
| File | UltiMaker Cura said | Actual problem | Result |
|---|---|---|---|
| 40 × 20 × 12 mm block saved in meters | Auto scaled model to 100000% of original size | Clean solid at 1/1000 scale | 40 × 20 × 12 mm |
| Same block saved in inches | Auto scaled model to 10000% of original size | Clean solid at 1/25.4 scale | 157.5 × 78.7 × 47.2 mm |
| Same block saved in centimeters | No message | Clean solid at 1/10 scale | 4 × 2 × 1.2 mm |
What is going on
Cura scales a model up when it is more than 100 times smaller than the build volume in every direction, rounding the factor down to a power of ten (source). The preference "Scale extremely small models" is on by default (source). The percentage therefore depends on the printer: on the Ender-3's 235 × 235 × 250 mm volume, a meter file gets 100000% and an inch file 10000%. A file in centimeters is only 10 times too small, so Cura leaves it alone without a message.
The mesh itself is fine; FixSTL reported each file as a clean solid at its stored size.
What was actually wrong
How to fix it
- Compare the size under the object list with the size you designed.
- File saved in inches: scale the model to 25.4% (157.5 mm becomes 40 mm).
- File saved in centimeters: scale it to 1000%.
- Fix the export so the next file is in millimeters; to stop the automatic scaling, turn off "Scale extremely small models" in Preferences.
Source: Seen in our tests · UltiMaker Cura 5.13.0 on macOS