What is the Arachne wall generator?
Arachne is an algorithm for generating outer and inner walls. Instead of relying on nearly fixed extrusion widths, it can make paths wider or narrower to match the actual model geometry. OrcaSlicer offers both Classic and Arachne wall generators.
Why variable line width helps
A model wall is rarely an exact multiple of a fixed extrusion width. A 0.70 or 1.05 mm local wall can be awkward to fill with nominal 0.42 mm lines. A fixed strategy may leave gaps, add special gap fill or omit a detail. Arachne can redistribute widths across the available space. This is especially useful for thin ribs, small lettering, organic contours and changing wall thickness.
Arachne is not automatically better
Classic can still be the cleaner comparison for simple geometry and large smooth cosmetic walls. Variable width also means variable commanded flow. If Flow Ratio or Pressure Advance is poorly calibrated, transitions can become more visible. An artifact that appears after switching to Arachne is therefore not proof that Arachne itself is the root cause.
Important controls
OrcaSlicer exposes minimum wall width, minimum feature size, wall transition controls and, in current 2.4 releases, Maximum Wall Resolution and Maximum Wall Deviation. Lower values can preserve more contour detail, but increase slicing workload.
When Arachne is a strong choice
- thin walls or text disappear with Classic,
- wall thickness changes frequently,
- Classic creates many tiny gap-fill paths,
- complex contours do not divide cleanly into fixed line widths.
When to compare Classic
- large smooth visible walls,
- simple technical parts with constant wall thickness,
- new surface artifacts appeared only after switching generators.
Practical workflow
- Slice with both generators.
- Compare line-width and feature preview.
- Inspect critical details, wall count and overhang support.
- For dimensional errors, check flow, Pressure Advance and XY compensation before blaming the wall generator.
Arachne is best understood as a geometry tool, not a universal “quality mode”.