HOW TO FIX ZITS AND BLOBS ON 3D PRINTS

Zits and blobs are small raised bumps on the surface of a 3D print. They appear at the point where a layer starts and ends (the Z-seam), or randomly across surfaces. They're caused by excess pressure in the nozzle that forces out a tiny extra blob of filament.

Zits and blobs have several causes: • Z-seam placement — Every layer starts and stops somewhere. Where these seams line up determines where you see the most visible blobs. • Retraction settings — Insufficient retraction at the end of a wall, or too much priming at the start, leaves excess material. • Coasting not enabled — Without coasting, the extruder is still pushing filament right up to the seam point. • Pressure buildup — During extrusion, pressure builds in the nozzle. When the extruder stops (at a seam or retraction point), residual pressure pushes out a blob. • Wet filament — Moisture in filament creates steam, which causes random bubbles and zits. • Temperature too high — Over-fluid filament is harder to control.

First, configure your Z-seam. Set it to "Sharpest Corner" in Cura or "Nearest" in PrusaSlicer. This hides the seam at corners where it's least visible. For cylindrical objects, use "Aligned" to create one consistent seam line rather than random bumps. Enable coasting: this stops extrusion slightly before the end of each wall, using residual pressure to complete the line. In Cura, set coasting volume to 0.04–0.08 mm³. Tune retraction: increase extra restart distance to a small negative value (-0.02 to -0.05 mm) to slightly reduce the prime after retraction. Lower nozzle temperature by 5°C. Less fluid filament is easier to control. Enable Linear Advance (Marlin) or Pressure Advance (Klipper) in your firmware. These features compensate for pressure buildup automatically and are the single most effective fix for zits. Dry your filament if you notice random (not seam-aligned) blobs.

Always configure your Z-seam position in the slicer. Enable Linear/Pressure Advance if your firmware supports it. Store filament in dry conditions. Print a small test cube to verify seam quality before long prints.