Version

PrusaSlicer Version 2.2.0

Operating system type + version

Windows 10 64-bit

3D printer brand / version + firmware version (if known)

Prusa MK3S (Modified, custom firmware based on FW 3.9.0). Note, no problem exists with the machine, the issue exists with G-Code generation of support material

Expected Behavior:

• Support material paths should be extruded only once per layer. At most, nozzle may "cross over" its own path, but should never re-extrude the same line twice in a single layer.
• If any part of a support path cannot be traced without the nozzle re-extruding the same path segment twice, a retraction should be executed so the nozzle can move to the appropriate location and begin extruding again.

Actual Behavior:

• Some segments of support structures are double-extruded on each layer. This results in excessive plastic buildup, nozzle crashes, layer shifts, etc.
• Double-extrusion frequently occurs at "loose ends" of support material near perimeter edges of large models. Sometimes occurs in internal support structure area at locations where rectilinear support paths re-converge.
• Nozzle crashes are especially prevalent when extruding wide layers (~ 1.5x nozzle orifice dia) as excess plastic cannot "run off" to the sides as easily. Can be mitigated by using slim extrusion widths (~1.1x nozzle orifice dia), but double-extrusion behavior should not occur in the first place.
• Occurs for "Rectilinear" & "Rectilinear Grid" support structures only. Does not occur for Honeycomb supports, where each support segment is only traced once. Does not occur when extruding features of the sliced part itself.

Steps to Reproduce:

• Place moderate or large STL (100x100mm+) onto build plate. Use part with large overhangs or incline to ~30degrees such that large areas of support structures are required.
• Enable supports and auto-support generation using Rectilinear or Rectilinear Grid support pattern
• Slice file. Many areas of resulting support structure will be double-extruded each layer (see red circles in attached photo)
  

Project File (.3MF) where problem occurs

Example.zip