What bulging layers look like
Layers bulge outward, the top surface is rough with ridges, and dimensions come out slightly large. Small features fill in and lose detail.
Why the printer over-extrudes
Simplify3D's under-extrusion guide explains that the slicer estimates how much plastic to push, but the printer gives no feedback on how much actually leaves the nozzle. When too much comes out, you get over-extrusion: the direct levers are the extrusion multiplier (the flow rate) and the filament diameter the slicer assumes.
Flow settings to change
- Extrusion multiplier — Simplify3D calls this the flow rate: going from 1.0 to 1.05 extrudes 5 % more plastic. It is typical for PLA to print near 0.9 (ABS is closer to 1.0). For over-extrusion, lower the multiplier in 5 % steps and re-test. (Simplify3D under-extrusion guide)
- Filament diameter — first confirm the slicer has the real diameter (most common are 1.75 mm and 2.85 mm); measure with calipers. An overstated diameter makes the printer over-extrude. (Simplify3D under-extrusion guide)
Testing with a calibration cube
Print a 20 mm tall cube with at least 3 perimeter outlines and check the top: the perimeters should be fused with no bulging, and the walls close to the expected size. Lower the multiplier in 5 % steps and re-measure until the top surface is smooth and the sides stop bulging.