YouTuber demonstrates method for cleaner bridging in FDM 3D printing

Anyone who prints using FDM is familiar with the problem: cantilevered bridges tend to sag and look stringy. The maker behind Make Wonderful Things has systematically investigated this issue and achieved significantly better results. His approach seems trivial, but is based on consistent testing with three parameters: bridge flow, bridge speed, and extruder temperature.

“Bridging” refers to printing paths across a gap without underlying layers as a support. The strands behave like taut ropes and often do not adhere sufficiently to their neighbors. This is where bridge flow (BF) comes in, i.e., the targeted over- or under-feeding of the bridge segment, which the slicer applies only to these paths.

In the experiment, he increased BF above 1.0, which resulted in wider extrusions and better line adhesion. At the same time, he reduced the bridge speed (BS) to 10 mm/s. The combination of more material and slower speed gives the strands time to tension and bond laterally instead of sagging loosely. Temperature remained a variable because plastic that is too hot sags and plastic that is too cold adheres poorly. Many gaps disappeared on the test snippets and the edges became cleaner. Corners still show residual sagging, and the developer is continuing to search for a robust solution here. It is also important to have a uniform geometry of the bridge surface, as varying spans create unpredictable sagging.

If you want similar results, it is best to start with BF just above 1.0, reduce BS significantly, and check the effect step by step on small test pieces before tackling productive parts. Make Wonderful Things provides the test models and measurement series on the project page. This allows you to cleanly document your own profiles in the slicer and compare them in a reproducible manner. The approach is pragmatic and suitable for common FDM devices with Bowden or direct drive extruders. Because the parameters only affect bridging segments, the rest of the print path remains unchanged.