Flexible filament bends in the feed path when the force needed to push it exceeds its buckling resistance. Friction, tight bends, excessive idler pressure, a long tube and high back pressure are the main causes.
Map the feed path
- Spool payoff
- Guide tube bends
- Extruder entry angle
- Nozzle back pressure
Reduce friction and pressure
Use a short, smooth path, avoid sharp bends and keep the spool free. Lower the speed and retraction, and verify that the nozzle is not partially blocked. Heat creep can also soften the filament before the drive gears.
Adjust the feeder
- Moderate idler tension
- Clean drive gear
- Correct diameter
- Support the filament
Validate at production speed
Run the same path and speed as production. If bending appears only at high flow, the limit is pressure or temperature, not just the feeder.
| Cause | Symptom | Control | Action |
|---|---|---|---|
| Long tube | S-bend or buckle | Path length | Shorten |
| High friction | Stalling | Tube and guides | Reduce friction |
| High back pressure | Filament bows | Nozzle and temperature | Clear or heat |
| Excess idler | Filament deforms | Tension screw | Reduce |
| Wet filament | Variable stiffness | Drying | Dry TPU |
Common engineering mistakes
- Increasing idler pressure.
- Ignoring tube bends.
- Using high retraction.
- Testing at low speed only.
- Not checking nozzle condition.
Checklist
- Is the path short?
- Is friction low?
- Is idler pressure correct?
- Is the nozzle clear?
- Does the fault repeat at production speed?
Describe your feed path through the quote form for a TPU review.