YouTuber measures breaking forces: Toolpath tuning noticeably changes FDM strength

By default, many slicers first print the outer walls of FDM parts and then add the infill to the component. Maker NeedItMakeIt investigated a potential weak point in this sequence and tested an alternative line layout. The focus is on the question of how strongly layer adhesion depends on temperature and deposition distances during printing.

Using a thermal imaging camera, NeedItMakeIt observed that the walls printed first have time to cool down. If the printer later deposits infill against or on top of them, fresh material more often encounters already cooled paths. This can impair the connection between the strands. As a countermeasure, he used an aligned, rectilinear infill pattern for solid areas. In this case, the printer typically extrudes directly next to the last layer deposited, which is still warm. In addition, the pattern is vertically aligned, which could improve adhesion at the transition points between layers.

For comparison, he printed a lever-like test piece and measured the force required to break a column out of the base. He compared three variants: a standard infill pattern, the aligned infill, and the aligned infill with a single outer wall. The tests were carried out with PLA, normal PETG, and carbon fiber-reinforced PETG.

The results varied depending on the material. With aligned infill, the strength of PLA and carbon fiber-reinforced PETG increased by about 46 percent. With normal PETG, however, the aligned pattern performed worse than the standard setting. The variant with aligned infill plus an outer wall also showed mixed results: it was above the standard variant for PLA, but below it for both PETG versions. NeedItMakeIt concludes that the aligned pattern is particularly helpful when adhesion between layers is otherwise limited. If adhesion is already good, as in its PETG tests, the pattern may be weaker as an overall structure.