Spiral Vase seam on smooth objects / Spiral vase not following object contour

[fritzw]

Is there an existing issue for this problem?

• I have searched the existing issues

OrcaSlicer Version

2.1.1 and 2.2.0 RC

Operating System (OS)

Linux, Windows

OS Version

Mint 22, Windows 11

Additional system information

irrelevant

Printer

irrelevant

How to reproduce

• Add standard cone primitive to build plate
• Switch to vase mode
• Slice
• Notice seam-like artifact in preview and in print

Actual results

Print shows a "seam-like" artifact on the smooth surface of the cone:

The problem becomes more severe for more severe overhangs (making the cone wider but not taller). Here's the same cone but scaled down from 25.6mm to 9mm height:

The root cause seems to be that the slicer cuts the object into horizontal slices as usual in the "normal" non-spiral mode, and then joins them afterward to create a spiral, instead of following the actual surface of the object in a spiral trajectory. This can be seen by overlaying a circle on the preview, which aligns perfectly with the contours of the toolpath. This should not be the case if the toolpath was an actual spiral ascending a cone:

Activating the "Smooth spiral" mode merely hides the fact by blending the seam over a larger distance. Nevertheless, most of the extrusion path is still circular and does not faithfully follow the contour of the object. Only about 1/3 of it actually approximates a spiral due to the smooth blending:

Expected results

• There should be no seam in vase mode for a smooth object
• The toolpath should faithfully follow the contour of the object as Z increases, not follow the contour of the object at a single Z height.

Project file & Debug log uploads

orcaslicer_vase_mode_bug.zip

Checklist of files to include

• Log file
• Project file

Anything else?

• Not sure if this this is the same as Still issues with vase mode / spiral mode after "full re-write of spiral vase" (1.9.1) #4298 because that mainly deals with complex models. This issue occurs even with very simple shapes like a cone.
• PrusaSlicer appears to do the same "blending" of circular paths as the "Smooth Spiral" mode, as far as I can tell from drawing circles on Screenshots.