Over Extrusion and Blobs: Diagnosis and Fix

Jackson B.

Too Much of a Good Thing

Over extrusion is when the printer deposits more filament than calculated for a given path segment. The result manifests as several characteristic defects: walls that are thicker than specified, surfaces with blobs and zits where excess plastic accumulated, dimensions that are larger than designed, and in severe cases, the nozzle dragging through previously extruded material. Understanding the causes and working through them systematically resolves over extrusion without guessing.

Over extrusion and under extrusion are related problems, and both indicate that the actual extrusion rate doesn't match the commanded rate, just in different directions. The diagnostic and correction approach is similar: work through potential causes systematically rather than randomly adjusting settings. The most common causes of over extrusion are distinct from under extrusion causes, though some (like incorrect e-step calibration) can cause either problem depending on the direction of error.

Causes and Fixes: Systematic Approach

Cause 1: Flow rate too high. 

• The most direct cause is the slicer's flow rate multiplier is set above 100% (or higher than calibrated). Check your filament profile's flow rate setting. If it's been set above 100% as a "fix" for another problem, investigate the root cause rather than compensating. Reduce to 100% and run a fresh flow rate calibration.

Cause 2: E-steps calibrated too high. 

• The extruder is commanded to move 100mm but actually moves 105mm. Verify with the 100mm extrusion test (see our e-steps guide) and correct if necessary. This problem affects all filaments equally, which is a useful distinguishing factor from per filament flow rate issues.

Cause 3: Pressure advance is miscalibrated high. 

• Pressure advance over compensation can cause over extrusion at the start of extrusion lines. If blobs specifically appear at the start of new perimeter lines after direction changes, suspect the PA K-value is too high. Reduce and retest. See our PA calibration guide.

Seam Blobs Specifically

Blobs specifically at the seam point (where each perimeter layer starts and ends) are a common and distinct issue. The nozzle parks briefly at the seam while changing direction, and accumulated ooze drops at that point. Fixes: enable seam scarf (available in OrcaSlicer), which overlaps the seam ends smoothly. Use "Random Seam" mode to distribute blobs around the model. Enable "Wipe Before Retract," which moves the nozzle along the wall while retracting, mechanically shearing the forming blob. Pressure advance calibration also directly reduces seam blobs by compensating for the pressure difference at the seam point. Quality filament with a consistent diameter reduces the variability that contributes to inconsistent seam behaviour.