When scarf is enabled, seam placement shifts location by one scarf length from expected position. #45

New Issue

MrUnknownDE · 2026-04-05T16:18:15+02:00

MrUnknownDE commented

2026-04-05 16:18:15 +02:00

Originally created by @derei on 4/1/2026

Is there an existing issue for this problem?

I have searched the existing issues

OrcaSlicer Version

2.3.2

Operating System (OS)

Windows

OS Version

10

Additional system information

Not relevant for this bug.

Printer

Bambu Lab A1 Mini

How to reproduce

Load a simple model with a clearly visible external perimeter seam.
Place the seam at a known location, either by manual seam painting or by automatic placement in a predictable corner.
Slice with scarf disabled and inspect seam preview.
Enable scarf seam and slice again without changing seam placement inputs.
Compare seam preview locations.
Optionally print both versions to verify that the printed scar matches the previewed seam location.

Scarf OFF
seam placement appears where expected

Scarf ON
seam placement is automatically shifted by one scarf length

Scarf ON and Reverse-on-Even ON (applied to external perimeters too)
seam placement appears twice, due to reversing

Showing how line start/end and seam placement relate when Scarf is ON:

... and also with Reverse-On-Even Enabled

Actual results

With scarf disabled, the seam preview appears where the user would expect it to be.
With scarf enabled, the seam preview shifts to the end of the scarf overlap.

This behaviour is consistent in automatic and manual seam placement.
Also, with reverse on even enabled for external perimeters, the shifted seam preview appears on both sides on alternating layers, producing two scar tracks.

Which points to another issue:

The manual seam painting seems to mark the "start of the perimeter line", and not the end, where the seam usually leaves a scar (either dip or blob).

Note:
The observed scars on the printed parts coincide with where the seam is seen in the preview. This confirms the end of the perimeter line is the one responsible with generating scars.

Expected results

Enabling scarf should not move the seam placement location. It should only change how the seam is blended.
The seam preview should remain at the same seam placement location with scarf on and off.

Also, manual seam placement (painting) should be intuitive: to have the seam where it's painted, not to have it shifted with one scarf overlap length when scarf is on.

Project file & Debug log uploads

Dome - Truncated Icosahedron_for_bug-report.zip

Checklist of files to include

Log file
Project file

Anything else?

Proposed fix:

Fix the seam position logic. Currently it appears that Orca places the start of the perimeter line at the "designated seam placement", but the seam extrusion happens at the end of the perimeter line. Orca should ensure the end of the perimeter line is the one coinciding with the "designated seam placement", because that part is the one causing the scarring in general.
For Reverse-On-Even, the start of the lines should be shifted along the perimeter accordingly, so the ends are the ones that coincide with "designated seam placement", thus removing "double scarring".
Manual seam painting should also designate the end of the perimeter line position, not the start of it.

*Originally created by @derei on 4/1/2026* ### Is there an existing issue for this problem? - [x] I have searched the existing issues ### OrcaSlicer Version 2.3.2 ### Operating System (OS) Windows ### OS Version 10 ### Additional system information Not relevant for this bug. ### Printer Bambu Lab A1 Mini ### How to reproduce 1. Load a simple model with a clearly visible external perimeter seam. 2. Place the seam at a known location, either by manual seam painting or by automatic placement in a predictable corner. 3. Slice with scarf disabled and inspect seam preview. 4. Enable scarf seam and slice again without changing seam placement inputs. 5. Compare seam preview locations. 6. Optionally print both versions to verify that the printed scar matches the previewed seam location. **Scarf OFF** _seam placement appears where expected_ <img width="1311" height="901" alt="Image" src="https://github.com/user-attachments/assets/00f0d96b-9486-46e8-a387-6000d6f9577d" /> **Scarf ON** _seam placement is automatically shifted by one scarf length_ <img width="1310" height="898" alt="Image" src="https://github.com/user-attachments/assets/ac2c9419-2cad-4d7d-9457-5c1caaff298f" /> **Scarf ON and Reverse-on-Even ON (applied to external perimeters too)** _seam placement appears twice, due to reversing_ <img width="1322" height="899" alt="Image" src="https://github.com/user-attachments/assets/c0fac812-f733-4932-a7f3-0cd331931721" /> **Showing how line start/end and seam placement relate when Scarf is ON:** <img width="2068" height="701" alt="Image" src="https://github.com/user-attachments/assets/7d987644-4d8b-49ce-93be-62e10958394e" /> _... and also with Reverse-On-Even Enabled_ <img width="1257" height="867" alt="Image" src="https://github.com/user-attachments/assets/9e927b4d-9d97-4560-a308-c6a0741c764c" /> ### Actual results - With scarf disabled, the seam preview appears where the user would expect it to be. - With **scarf enabled, the seam preview shifts** to the end of the scarf overlap. This behaviour is consistent in automatic and manual seam placement. Also, with reverse on even enabled for external perimeters, the shifted seam preview appears on both sides on alternating layers, producing two scar tracks. **Which points to another issue:** - The manual seam painting seems to mark the "start of the perimeter line", and not the end, where the seam usually leaves a scar (either dip or blob). Note: The observed scars on the printed parts coincide with where the seam is seen in the preview. This confirms the end of the perimeter line is the one responsible with generating scars. ### Expected results Enabling scarf should not move the seam placement location. It should only change how the seam is blended. The seam preview should remain at the same seam placement location with scarf on and off. Also, manual seam placement (painting) should be intuitive: to have the seam where it's painted, not to have it shifted with one scarf overlap length when scarf is on. ### Project file & Debug log uploads [Dome - Truncated Icosahedron_for_bug-report.zip](https://github.com/user-attachments/files/26403646/Dome.-.Truncated.Icosahedron_for_bug-report.zip) ### Checklist of files to include - [ ] Log file - [x] Project file ### Anything else? **Proposed fix:** - Fix the seam position logic. Currently it appears that Orca places the start of the perimeter line at the "designated seam placement", but the seam extrusion happens at the end of the perimeter line. Orca should ensure the end of the perimeter line is the one coinciding with the "designated seam placement", because that part is the one causing the scarring in general. - For Reverse-On-Even, the start of the lines should be shifted along the perimeter accordingly, so the ends are the ones that coincide with "designated seam placement", thus removing "double scarring". - Manual seam painting should also designate the end of the perimeter line position, not the start of it.

MrUnknownDE added the bug bug bug bug bug bug bug bug bug bug bug bug bug bug bug bug bug bug bug bug bug labels 2026-04-05 16:18:15 +02:00

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Reference: github/OrcaSlicer#45