Arachne perimeter generator creates distorted perimeters in high-precision STL files (Classic works fine)

[NoidNouser]

Is there an existing issue for this problem?

• I have searched the existing issues

OrcaSlicer Version

2.2.0

Operating System (OS)

Windows

OS Version

Windows 10

Additional system information

No response

Printer

Artillery X4 Plus S1

How to reproduce

1. Export an STL file from a high-precision CAD workflow, ensuring a high-resolution mesh with settings like:

• Sag: 0.001 mm
• Step: 0.001 mm
• Grouped mode enabled (when available)

2. Import the STL into OrcaSlicer (Tested on version 2.2.0).

3. Set precision in slicer settings as follows:

• Resolution: 0.012 mm (Even reducing it to 0.001 mm does not solve the issue)
• Closing radius: 0.049 mm

4. Slice with Arachne perimeter generator (Default settings).

5. Observe the distorted perimeters in the preview and in the final print.

6. Change the perimeter generator to Classic and slice again → The issue disappears.

Actual results

I noticed that the Arachne perimeter generator produces distorted perimeters when slicing high-precision STL files. The issue does not occur when using the Classic perimeter generator.

The STL models are created from Class A surfaces, ensuring high precision and smooth geometry. However, Arachne struggles to generate clean perimeters, especially on curved surfaces.

Expected results

Arachne should generate perimeters without distortion, maintaining the same quality as the Classic generator.

Project file & Debug log uploads

Classic_vs_Arache.zip

Checklist of files to include

• Log file
• Project file

Anything else?

This happens with STL files from different sources, always ensuring high surface quality.
Using Classic fixes the issue, but Arachne should ideally handle these cases better.
Adjusting Arachne’s transition width, minimum perimeter width, and other parameters does not solve the issue.
The problem is more visible on curved surfaces or complex geometries.
Even lowering the resolution to 0.001 mm does not fix the problem.