Glossary · Setting

3D printing

Z seam

The vertical line of small dots or bumps that is visible on many prints. It forms where each outer wall begins and ends.

Explained in more detail

Every outer wall is a closed loop that has to start somewhere and end at the same point. At the start, pressure in the nozzle has to build up first, at the end some material oozes on, and a tiny gap can be left in between. Because every layer begins at such a point, a seam forms over the height of the part. In FDM printing it cannot be avoided entirely, but it can be controlled: slicers offer positions such as Aligned, Nearest, Random or Back, and in PrusaSlicer, OrcaSlicer and Bambu Studio you can paint the seam directly onto the model. How noticeable it is also depends on pressure advance, flow, wipe and the scarf seam.

Where does the term come from?

The Z stands for the vertical axis of the printer: the seam runs vertically upwards through all layers. In English it is called z seam.

In practice

• For angular parts, place the seam in a corner, where it almost disappears.
• For round parts, place the seam at the back or choose Random, which spreads the flaws across the surface.
• A thick, untidy seam often indicates uncalibrated pressure advance or too high a flow.
• According to the OrcaSlicer documentation, the scarf seam by default lets the line ramp up and fade out over about 20 mm, which helps mainly on smooth, round surfaces.
• For figures, paint the seam into a fold or edge.

Not to be confused

The Z seam is not a layer shift and not a defect of the printer: it occurs in every FDM print and can only be hidden or reduced. Not to be confused with stringing, that is fine strands between parts.

Frequently asked questions

Can you avoid the Z seam completely?

No, in FDM printing every closed outer wall has a start and an end point. The exception is vase mode, in which the printer prints a continuous spiral without stopping.

Which seam position is the best?

For angular parts use Aligned, for parts with a clear front use Back, and for round, smooth parts use Random or the scarf seam. The most accurate approach is to paint the seam in the slicer itself.