Hiding the Z seam: setting the seam position correctly
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You will see a vertical line of small dots or bulges running along the whole height of many prints. That is the Z seam. With FDM printing it cannot be prevented completely, but you can control where it sits and how noticeable it is.
What is the Z seam?
Every outer wall is a closed loop. The printer has to start somewhere and stop at the same point. Small flaws arise at this spot:
- At the start, pressure in the nozzle has to build up first, so the line is briefly too thin or a small blob comes out.
- At the end, some material still oozes out, producing a small bump.
- A tiny gap can remain between the end and the start.
Since every layer begins at such a spot, a seam forms along the height. How visible it is depends on the seam position and on calibration.
The seam position options
The names differ slightly depending on the slicer. The basic idea is the same everywhere.
| Option | What happens | Good for |
|---|---|---|
| Aligned | The seam sits in the same place in every layer, preferably in corners | most parts; a straight line is easy to hide |
| Nearest | The seam is wherever the nozzle happens to be, preferably in inner corners | quick prints where looks do not matter |
| Random | A different place in every layer | round parts without corners, vases |
| Rear (Back) | The seam is on the back of the part | parts with a clear front |
| Aligned back (OrcaSlicer) | Like Aligned, but shifted to the back | figures, decorations |
Aligned
The default in many profiles, including Bambu Studio and OrcaSlicer. The seam is placed in a corner or edge wherever possible. On angular parts it almost completely disappears there. On round parts it forms a continuous line, which you can deliberately move to the back.
Nearest
Saves travel moves and therefore a little time. However, the seam jumps between different places, which looks untidy on visible parts.
Random
Spreads the flaws over the whole surface. There is no line, but many small dots that make the surface look slightly rough. Good for smooth, round shapes without corners. According to OrcaSlicer, this can slightly increase strength, because the weak point is not always in the same place.
Rear
Places the seam on the back, that is, towards the back of the print bed. Handy if you orient the part so that the front faces forward.
Sharp corners
Not every slicer has a separate “sharp corner” option. Instead, Aligned and Nearest prefer corners on their own, especially concave inner corners. Cura also has the “Seam Corner Preference” setting, which lets you decide whether the seam should be hidden in inner or outer corners. On angular parts this is the simplest way to make the seam almost invisible.
Painting the seam
In PrusaSlicer, OrcaSlicer and Bambu Studio you can set the seam directly on the model. With a brush tool you mark areas where the seam should sit, or block areas for it. In Cura there is instead a user-defined seam position via coordinates. This is the most precise method for figures and decorations: put the seam in a fold, an edge or on a back side where nobody sees it.
Wipe and seam gap
These settings make the seam itself smaller, wherever it sits:
- Wipe: After the end of the outer wall, the nozzle travels a little further, often slightly inwards into the part. In doing so it wipes off oozing material. In OrcaSlicer this is called “Wipe on loops”, among other names.
- Seam gap: Leaves a tiny gap at the end of the loop so that the start and end do not overlap and form a bulge. The OrcaSlicer documentation gives 0 to 15 % of the nozzle diameter for well-tuned printers.
- Wipe before the outer wall: OrcaSlicer can shift the start point of the outer wall slightly inwards so that a blob at the start is not visible on the outside.
Scarf seam
The scarf seam is a newer technique offered by OrcaSlicer, Bambu Studio and PrusaSlicer. Instead of starting and ending the loop abruptly at one point, the line is started with a gradual ramp up over a distance and overlapped at the end with a gradual run-out. This produces a smooth transition instead of a butt joint.
According to the OrcaSlicer documentation:
- Length: about 20 mm as the default
- Steps: 10, which is usually enough
- Speed: below 100 mm/s for the outer wall, otherwise the result suffers
- Seam flow: leave at 100 %
The scarf seam works best on smooth, round surfaces. On sharp corners and overhangs it does little. The “conditional scarf seam” variant therefore applies it only where a normal seam would be noticeable. The print takes slightly longer.
Connection with pressure advance
A thick, untidy seam is often not a problem of seam position but of calibration. Without well-tuned pressure advance, too little material comes out at the start of a line and too much at the end. This is exactly what you see at the seam. Too high a flow also makes it thicker. Prusa therefore names Linear Advance and the extrusion multiplier as the most important levers for an inconspicuous seam. How to set both is explained in Calibrating your 3D printer.
Also helpful: a slower outer wall (see Print speed) and dry filament, because damp material spits more at the start of a line and pulls strings, see Stringing.
How to proceed
- Choose the seam position to suit the part: aligned for angular parts, rear for round ones, or random.
- On visible parts, paint the seam onto an edge or the back.
- Calibrate pressure advance and flow.
- Enable wipe and adjust the seam gap if needed.
- Try the scarf seam on round, smooth parts.
Continue with: Walls and top layers.