A tray that came out whiskered
You finish a small parts tray with a dozen slots, and every slot is bridged with a hair of PLA — a thin strand where the nozzle travelled, with a tiny blob at each stop. The part is ruined by oozing, and it is almost always retraction or temperature, not the filament.
The two levers
Simplify3D's stringing and oozing guide describes it as filament oozing out of the nozzle while it travels. The two levers are retraction (distance and speed) and temperature. PLA strings less than PETG, so the retraction usually does not need to be extreme.
Retraction and temperature, by the numbers
Each number below is quoted from the Simplify3D stringing and oozing guide.
- Retraction distance — for a direct-drive extruder use roughly 0.5–2.0 mm; for a Bowden setup the longer tube needs more, as high as 15 mm. Increase in small steps and retest. (Simplify3D)
- Retraction speed — the sweet spot is about 20–100 mm/s (1200–6000 mm/min). Too slow lets filament ooze; too fast can grind or separate the filament. (Simplify3D)
- Nozzle temperature — if retraction is already correct, lower the extruder temperature by 5–10 °C. (Simplify3D)
Testing the result
Slice a flat comb or a part with several small teeth and run it after each single change. The fix is right when the gaps between the teeth are clean and the teeth stay sharp. If a blob remains at the start of a move, raise retraction speed before adding more distance — distance is the last lever to pull.