Bug Report: Print cooling fan behavior doesn’t match G-code on A1 mini (Firmware 01.04.00.00)
Printer: Bambu Lab A1 mini
Firmware version: 01.04.00.00
Material: PETG
Slicer 1: OrcaSlicer 2.3
Slicer 2: Bambu Studio 2.0.2.57
Model: (attached)
Issue summary:
During overhang printing, the cooling fan (M106) behaves inconsistently with the G-code and preview.
The fan:
- may turn off too early,
- or never turn on,
- or turn on briefly but revert instantly to a previous value.
This results in poor cooling during narrow or long overhangs.
Case 1: OrcaSlicer 2.3 – “Start fan early” setting enabled
1. Screenshot: OrcaSlicer setting: “Start fan early by 0.5s” = enabled
2. Screenshot: Preview shows fan at 100% for both inner and outer overhang walls
3. Screenshot: Paint annotation of nozzle path shows:
- Fan turns off too early, right at the start of a long overhang
- It never turns back on, even though G-code expects 100%
Case 2: OrcaSlicer 2.3 – “Start fan early” disabled
4. Screenshot: Setting disabled
5. Screenshot: G-code preview: 100% fan only for overhangs
6. Screenshot: Annotated nozzle path shows:
- Fan turns on briefly
- Immediately reverts to the previous value before overhang is complete
Case 3: Bambu Studio 2.0.2.57 preview
7. Screenshot: Fan speed preview in Bambu Studio
- Outer overhang walls are marked for 100% cooling
- Inner overhangs are not cooled (treated as non-overhangs)
8. Screenshot: Real behavior sketch
- Cooling does not match preview or G-code
- Fan turns on/off in unpredictable patterns
Expected behavior:
- Fan speed from
M106should follow G-code strictly - Especially on overhangs where consistent airflow is required for print quality
Actual behavior:
- Fan doesn’t follow G-code commands as expected
- Inner overhangs remain uncooled despite preview showing airflow
- Real fan behavior contradicts both slicer preview and inserted
M106commands
Attachments:
-
Screenshots 1–8
-
Model file (.3mf)
Overhang test.3mf (31.2 KB)
