Grinding / Stripping
The extruder drive gear chews through the filament instead of pushing it forward. Once a groove is carved, the gear loses grip and extrusion stops entirely.
Critical severity
Extrusion
What It Is
The extruder drive gear chews through the filament instead of pushing it forward. Once a groove is carved, the gear loses grip and extrusion stops entirely.
How It Forms
The drive gear has teeth that grip the filament surface. When the gear pushes but the filament can’t move (back-pressure too high), the teeth carve into the same spot repeatedly. The filament develops a flat groove. Once the groove is deep enough, the gear teeth spin inside it without engaging — like a stripped screw.
This is a cascading failure: the more it grinds, the less it grips, the more it grinds.
Visual Signature
- Clicking/popping sounds from the extruder
- Filament shavings/dust around the gear
- Sudden under-extrusion that worsens rapidly
- Print stops extruding mid-way through
- Flat spot visible on filament when pulled out
Root Causes
| Cause | Calibration Variable | Direction |
|---|---|---|
| Too many retractions in one area | Retraction | ↑ (distance or frequency) |
| Temperature too cold (filament too stiff) | Extrusion Temp | ↓ |
| Nozzle clogged (back-pressure) | — (maintenance) | — |
| Extruder tension too high | — (hardware) | ↑ |
| Printing faster than hotend can melt | Max Volumetric Flow | exceeded |
How the Auto-Tuner Detects It
- Roller encoder: Actual movement drops while motor is still commanding → grinding detected immediately
- Audio (future): Characteristic clicking pattern detectable by microphone
How the Auto-Tuner Fixes It
- Live tuning: Instant pause when encoder detects slip. Reduce speed, raise temp, reduce retraction.
- Prevention: Calibrated retraction limits, volumetric flow limits prevent the conditions that cause grinding