Rich Felker

Coasting could help confirm if this is the cause but it's not a solution. It would cause severe underextrusion of outer walls and other structures that aren't redundant.

I'm not using the frontend, only CuraEngine, so what would you like as the "project file"? Would the json config file I pass with `-j` work for you?

I've played with multiple perturbations of settings that might affect excess material in the walls, including even lowering inner wall flow by as much as 80%, with no major change....

Further update: problem disappears entirely with `wall_line_count=1` (and `infill_line_distance=0`) which produces just one outer wall and one "inner wall" (the outer wall of the inner surface). It's possible that's just...

Looking at the output with an analyzer, the affected layers have something like 2.4-3.0 mm² more material extruded with Arachne than with stable, but less with the 80% extrusion modifier...

> Could it be that there were gaps in between the walls in 4.9 that allowed the material to flow in? Yes, I think this is very likely. But it...

Command line and files to reproduce: ``` CuraEngine slice -j my.def.json -s support_enable=true -s support_type=buildplate -s layer_height=0.12 -s layer_height_0=0.12 -l d20crht.stl ``` [arachne_warts.zip](https://github.com/Ultimaker/CuraEngine/files/6460210/arachne_warts.zip) Most of the config is likely not...

Most prominent layer heights at which warts appear: - 8.64-8.88 - 9.48 - 15.84+

The warts are where the seam would be, but normally I don't have any bulge from a seam, certainly nothing on the order of the nozzle width. So something else...

I'm going to run some tests to see if it's just overextrusion exposed by Arachne's more thorough filling. Measured by filament length moved, my esteps are slightly underextruding (by ~1-2%)...