The seam is a kind of gap between the start point and the end point of each perimeter of the layer( Unless you enable the Spiral Vase mode, refer to Spiral Vase | Bambu Lab Wiki). It leaves vertical seams on the surface of the model, which is unavoidable in FDM 3D printing. Seams can be well hidden on irregular surfaces such as those with concave and convex vertices. On the other hand, some models with circular surfaces (such as cylinders) will not be able to hide the seams, which will be very obvious.
As shown in Fig.2-2, the white points are the seams of layer 53.
For better print quality, the seam position can be set in the process presets. There are four types of seam positions to choose from: Recent, Aligned, Back, and Random.
“Nearest” first finds all possible candidate positions by the following priority: concave non-overhang vertex > convex non-overhang vertex > a non-overhang vertex > overhang vertex.
That is, it will preferentially select concave or convex non-overhanging vertices to make the seam position better hidden. If your model has sharp corners, this will make the seam effectively invisible.
However, if the current layer does not have either of these vertices available, it selects from among the other candidate non-overhang vertices so that it is closest to the end of the previous print path. As a result, this option optimizes the traveling path to minimize the impact of filament stringing.
The seam placing logic is the same as “Nearest” for finding the candidates, but it will choose the one that is nearest to the start point of the previous layer. This will ensure the seam is mostly aligned throughout the whole object.
The seam will be set behind the model. If you want to get a smooth surface in the front, such as an Iron Man mask, it will be a good choice.
Random seams will select a different location on each layer to place the seams, making the seams look less uniform and less obvious than "aligned" or "back". But it will cause some "zits" effects on the surface of the model.
Sometimes the auto seam position may be not ideal, you can customize the seam position by manually painting the method. The seam painting function can be enabled here:
Specific operations are shown in the following GIF: