Bridging in 3D Printing: Everything You Need to Know

Using a 3D printer, whether for professional or hobbyist purposes, can be an exciting journey filled with surprises. However, not all surprises are positive; some may present challenges. We have previously discussed common printing issues like stringing, ghosting, and warping, providing tips to overcome them. Today, we want to shed light on another potential challenge in FDM/FFF 3D printing: bridging. When you hear the term “bridging,” you might think of a bridge, and you’re absolutely correct! In simple terms, bridging refers to extruding plastic between two points in an empty space or gap. However, it often results in undesirable extrusions that sag and deviate from the intended straight line, leading to poor bridging. Let’s explore how to address this issue effectively.

You may have come across the comparison of FDM 3D printing as a hot glue gun on a robotic arm. Visualizing the issue of poor bridging in FDM 3D printing can be done by imagining operating a hot glue gun while pulling the trigger. Even if the first dot of glue makes contact with a surface, the subsequent glue will likely drip down in the air. Bridging in FDM is somewhat similar; when attempting to apply material in the air between two points, it tends to sag and not maintain a perfectly horizontal position. This article delves into why this bridge-like structure often fails and provides specific insights on how to address it effectively.

Why your overhang or bridge doesn’t succeed in 3D printing can depend on several factors (photo credit: N3DTech via Prusa Forum).

Temperature, Material and Printing Speed Are Decisive Factors

Certainly, like any challenge in 3D printing, there are specific reasons why poor bridging can occur. Drawing from the earlier analogy of the hot glue gun, we can identify some clues that contribute to this problem. One key property is the temperature of the material. Just as with the hot glue gun, if we attempt to use liquid adhesive as a bridge between two points (A and B), the extreme temperature makes it challenging to achieve the desired result. Similarly, in 3D printing, improper filament heating can lead to issues. If the filament is heated excessively, it becomes highly viscous, causing it to drip excessively and resulting in significant bridging problems. Conversely, insufficient heating leads to low filament viscosity, causing it to sag due to gravity.