Blobs / Zits
Small bumps on the surface at points where the nozzle starts, stops, or restarts extrusion. Most visible along the Z-seam line.
Low severity
Extrusion
What It Is
Small bumps on the surface at points where the nozzle starts, stops, or restarts extrusion. Most visible along the Z-seam line.
How It Forms
Two main causes:
-
Seam point pressure surge — Each perimeter loop has a start and end point. When extrusion restarts, pressure builds before the nozzle starts moving at full speed. The brief excess deposits a blob. When the loop ends, residual pressure deposits another.
-
Post-travel restart — After a retraction + travel move, the extruder primes (pushes filament back). If priming is slightly too much, or starts too early, a small blob forms at the landing point.
Visual Signature
- Vertical line of pimples along the Z-seam
- Random small bumps on surfaces (post-travel blobs)
- More visible on smooth, flat surfaces
- Often one per layer, aligned vertically
Root Causes
| Cause | Calibration Variable | Direction |
|---|---|---|
| Pressure Advance not tuned | Pressure Advance | ↓ |
| Retraction/prime mismatch | Retraction | misconfigured |
| No coast/wipe settings | — (slicer) | — |
| Temperature too hot | Extrusion Temp | ↑ |
How the Auto-Tuner Detects It
- Camera: Surface analysis at seam line, comparing seam area to adjacent surface
How the Auto-Tuner Fixes It
- Calibration: Pressure Advance tuning eliminates most seam blobs. Retraction fine-tuning handles travel restart blobs.