Troubleshooting

Blobs and zits

Small bumps on the outside of a print, often lined up where each wall starts and ends.

Why they form

The nozzle stops and restarts every time it finishes one outer wall and moves on. Each restart can leave a little too much or too little plastic, and the mark it leaves is a blob or zit.

Watch an outer wall print. A mark that appears the moment the wall starts points to the restart. One that appears as the wall closes points to the stop.

Fixes

Mark at the start

The nozzle is priming too much plastic when it restarts. Reduce the extra length your slicer adds back after a retraction.

Mark at the end

Pressure in the nozzle keeps pushing plastic out as the wall closes. Turn on coasting or wipe while retracting so it stops a little before the end of the wall.

Retract less often

Set retraction to happen only when crossing open space, and have travel moves avoid crossing walls. Any ooze then stays inside the part.

Move the seam

Set the seam position to aligned or rear, or paint it onto a hidden edge, so the marks sit where nobody looks.

Sources

Simplify3D's blobs and zits guide covers retraction, coasting and seam placement. OrcaSlicer and PrusaSlicer name these settings differently, but the same controls are in both.

Common questions

No. Blobs sit on the wall, where the nozzle starts and stops. Strings are thin hairs across open space between parts.

It can reduce ooze, but check retraction and seam settings first. Too low a temperature brings under-extrusion instead.

Not on most prints, because each closed wall has to start and end somewhere. You can hide it, spread it randomly, or tune it until it is barely visible.

Specifications come from manufacturers' published pages and can change. Check your printer's current documentation before you change a setting or fit a part.