Seam Placement

Seam placement decides where each layer’s outer wall loop starts and ends. That start/stop concentrates artifacts (zits, tiny gaps, gloss/texture shifts), so the goal is to deliberately put them where they’re least visible: on a corner, a rear/non-cosmetic face, inside a cavity, or distributed when a single vertical “zipper” line would look worse.

TL;DR

Set seam placement on purpose: use Aligned/Fixed on a hidden corner or rear edge for the cleanest look, or Random on fully round parts to avoid a single vertical zipper line. If the seam has big blobs or pinholes, tune restart behavior (temperature, retraction/wipe/coast) after you’ve put the seam somewhere easy to inspect.

Seam Placement: pick the least-visible optionTopic-specific diagram for the concept, checks, and tradeoffs in this lesson.Cosmetic faceHas sharp edge?Aligned seamRound surface
Choose Aligned/Fixed to hide one seam line on an edge, Nearest to reduce travel (but watch where it lands), or Random to spread marks when a single zipper line is worse.

What the seam is (physically)

On every layer, the outer wall is a closed loop. The “seam” is where that loop closes: extrusion decelerates, stops, then restarts at the next layer. Because nozzle pressure is changing at that moment (plus retraction, wipe, and any coasting), the plastic flow is rarely identical to the rest of the wall, leaving a tiny blob, notch, gap, or gloss change.

When seam placement matters most

Seams show up most on smooth, continuous surfaces: cylinders, vases, rounded enclosures, and glossy filaments. They’re easier to hide on parts with corners, texture, chamfers, or any vertical feature that can “own” the seam. If you see a straight vertical line running up the print, your seam is being placed in nearly the same XY location layer after layer.

Common seam modes (and the trade-offs)

  • Aligned or Fixed: keeps the seam in one XY area each layer. Best when you can hide it on a rear edge, sharp corner, concave notch, or inside; worst when it lands on a front cosmetic curve (creates a zipper line).
  • Nearest: starts the loop at the closest point to the previous path to reduce travel. Can reduce travel-related stringing, but may move the seam onto whatever face happens to be closest on that layer.
  • Random: distributes seam points around the perimeter. Avoids one obvious zipper line, but can pepper a smooth surface with many tiny start/stop marks.
  • Corner/Concave preference (if available): tries to put seams on sharp corners or inward curves where the geometry breaks up the visual defect. Often the best “set and forget” option on boxy parts.

How to choose a seam strategy (practical workflow)

  1. Pick a “cosmetic face” and a “hidden face” (rear, underside, inside a cavity, or a face that will be against another part).
  2. If the model has a sharp vertical edge or corner you can hide, use Aligned/Fixed and place the seam there (back edge is a common choice).
  3. If the model is round and visible from all sides, try Random first to avoid a single zipper line; if Random looks speckled, go back to Aligned and choose the least-viewed direction in real use.
  4. If travel/stringing is your bigger problem than seam visibility, try Nearest to shorten travels, then confirm in preview and on the part that the seam didn’t migrate to the front face.
  5. If you can edit the model, add a deliberate vertical feature (ridge, flat, chamfer, text strip) and align the seam to it. An intentional feature usually looks cleaner than hiding dozens of random marks.

Seam-related print symptoms

One obvious vertical zipper line on the “front”

Likely cause: Seam is aligned on a smooth, cosmetic face

Fix: Switch to corner/concave preference or move the fixed seam to a rear edge/inside; if the part is fully round, try Random.

Seam has big zits/blobs

Likely cause: Too much pressure at restart (often temperature too high, retraction/wipe not tuned, or aggressive speed changes)

Fix: Lower nozzle temperature slightly and tune retraction/wipe/coast for cleaner restarts; keep seam placement constant while tuning so changes are easy to see.

Seam shows tiny gaps/pinholes

Likely cause: Under-extrusion right after restart (too much coasting/wipe, insufficient restart/prime, or inconsistent filament feed)

Fix: Reduce coast/wipe or add a small restart/prime if supported; re-check seam before changing other quality settings.

Random seam makes the surface look peppered or scuffed

Likely cause: Random distributes start/stop artifacts across the whole wall

Fix: Return to Aligned/Fixed and hide it on an edge/feature, or add a vertical design feature to conceal it.

Fast test to validate seam changes

  1. Slice a simple test shape: a smooth cylinder (hard mode) or a box with one clean face (easy mode).
  2. Print only 20–40 mm tall so the seam pattern is visible without wasting time.
  3. Change only seam placement first; keep temperature, speed, and retraction the same so you’re comparing one variable.
  4. Use slicer preview seam markers, then verify on the printed part. Pick the option that looks best for how the part will actually be viewed in use.