What over-extrusion is and how to confirm it
Over-extrusion is the opposite of under-extrusion: the nozzle deposits more plastic than the toolpath has room for. The extra material has to go somewhere, so it squeezes out sideways and upward. Walls bulge, top layers become ridged or wavy, small details blur, and the nozzle may drag through the excess and leave scars or blobs.
Confirm it by measuring. Print a 20 mm calibration cube and a single-wall box. If the cube measures 20.3 mm or more on X and Y, and the single wall is noticeably thicker than the set line width, you are over-extruding. Holes coming out undersize and parts that will not fit together are typical symptoms. A rough top surface with ridges between lines is another strong clue.
Before changing anything, rule out look-alikes. Elephant foot only widens the bottom few layers, not the whole part. Blobs at the seam come from retraction and pressure, not overall flow. And a first layer that looks over-squished is often a Z-offset issue rather than too much plastic. If the excess shows on every wall and every layer, flow is the likely cause.
Causes, most likely first
- Flow too high in the filament or print profile, sometimes 105 percent or more left over from an old tweak.
- Uncalibrated extruder steps or rotation distance.
- Wrong filament diameter in the slicer, such as 1.70 when the filament really measures 1.78.
- Filament with inconsistent diameter, common with cheap spools.
- Temperature too high, making plastic run more freely and ooze.
Fixes, cheapest and fastest first
1. Check the slicer profile
Look for a flow, extrusion multiplier or flow ratio setting above 100 percent and reset it. Confirm the filament diameter is set to 1.75 mm. Make sure the first-layer flow is not applied to the whole print by mistake.
2. Measure your filament
Use calipers at five or six places along a meter of filament. Good filament stays within about plus or minus 0.02 to 0.03 mm. If your average is off, enter the measured value in the slicer.
3. Calibrate the extruder
Mark filament 120 mm above the extruder entry, extrude 100 mm slowly with the hotend at temperature, and measure what remains. If 105 mm went in, reduce steps per millimeter or rotation distance proportionally. Save to firmware.
4. Fine-tune flow
Print a flow calibration test or a single-wall cube and adjust flow in 2 percent steps until the measured wall matches the line width. Many filaments end up between 92 and 100 percent.
5. Lower temperature a little
Drop 5 °C if the surface still looks wet or blobby. This also helps stringing.
6. Check top-layer settings
Ironing and high top-surface flow can mimic over-extrusion. Reset them to defaults while diagnosing.
Material notes
- PLA: the easiest to calibrate; profile flow is usually near 100 percent.
- PETG: often benefits from slightly lower flow, around 93 to 97 percent, because it swells and drags on the nozzle.
- ABS: similar to PLA; high temperatures in an enclosure can make it ooze more.
- TPU: compresses in the extruder, so measured flow varies with tension. Calibrate with the same tension you print with.
Prevention checklist
- Calibrate extruder steps once after any extruder change.
- Calibrate flow per filament brand and type, not just once.
- Measure filament diameter on new spools.
- Keep a log of the flow value that works for each filament.
- Avoid stacking adjustments in several places (printer, filament and process profiles).
- Print a calibration cube after major changes.