Map the marks to the sliced path
A seam marks where a closed perimeter starts and finishes. Look for a vertical row, a cluster at a corner, or scattered marks occurring once per layer. Open the exact sliced file and locate perimeter starts in preview. If the marks follow those locations, begin with seam placement. If blobs occur along uninterrupted lines, moving the seam is unlikely to solve their cause. Check for contaminated material, unstable extrusion, or pauses instead.
Choose a position for the actual object
For a display object with a hidden rear face, place the seam where that face will be. On a box, an existing corner can make the interruption less conspicuous. A cylinder has no natural corner, so a single straight seam may be easier to sand than random marks. Random placement trades one concentrated feature for distributed texture; it does not erase the start and stop events. Compare the actual intended viewing angle before deciding.
Separate placement from extrusion tuning
First print the same object with a different seam location while keeping temperature and flow unchanged. If the raised area moves with the seam, the placement diagnosis is supported. Only then consider the printer’s documented pressure, wipe, or restart controls. Large adjustments can turn a bump into a gap. Avoid copying pressure-advance values between extruders, materials, or firmware implementations.
Verify wall continuity
A short open container is useful because both outer and inner surfaces remain visible. Inspect the seam for a gap, raised ridge, or local weakness after cooling. Evaluate surface appearance and continuity separately: a hidden gap is still a defect. Keep a profile that gives a closed wall, then use location to manage appearance. Vase mode can avoid repeated perimeter seams for suitable single-wall objects, but it changes the structure and is not a general repair.
Choose between a hidden line and distributed marks
| Object | Placement to compare | What to inspect |
|---|---|---|
| Display shell with a defined rear | A seam on the hidden face | Check the actual displayed orientation and rear detail. |
| Box with corners | A seam associated with a suitable corner | Confirm preview places it there without damaging a mating edge. |
| Round container | Aligned versus distributed starts | Decide whether one cleanup line or distributed texture is preferable. |
| Part with a sliding fit | A location away from the contact surface where possible | Check continuity and fit, not only visibility. |
These are planning comparisons, not guaranteed results. A placement label such as “rear” may refer to bed coordinates rather than the face you call the back of the finished object. Inspect the exact preview after rotating or rearranging the model.
Example: a round cover that faces the viewer
Save two versions of the same short cover. In one, concentrate the perimeter starts on a hidden side where the slicer permits it. In the other, distribute them. Keep material, temperature, flow, layer height, and orientation fixed. Compare the cover from its intended viewing direction and check the inside for gaps.
If raised marks move with the previewed start points, placement is relevant. If irregular blobs remain elsewhere, do not keep painting new seam positions: investigate uninterrupted-path extrusion or pauses. This is a hypothetical comparison, not a measured Bambu or Prusa result.
Know what seam controls cannot establish
Hiding a seam does not prove that the wall is watertight or mechanically adequate. A negative appearance change also does not establish the correct pressure-advance or flow value. Use only the calibration method supported by your printer, firmware, and slicer; Bambu flow-dynamics settings and another firmware’s pressure controls are not values to exchange blindly.
If threads connect separate features, use the retraction-test guide instead. If missing lines appear away from perimeter starts, follow under-extrusion diagnosis. Keep placement changes separate from extrusion changes so the next comparison answers one question.
Seam comparison record
| Check | Evidence to keep |
|---|---|
| Path position | Match the mark to the perimeter start in the exact sliced file. |
| Location change | Keep temperature and flow fixed while moving the seam. |
| Wall result | Record raised material and missing material separately. |
Reference and limits
Prusa’s seam-position documentation describes perimeter starts and placement choices in PrusaSlicer. Other slicers and versions can expose different controls. The round-cover comparison is a proposed method, not a measured surface-quality or strength result.