When is support material necessary in FDM printing?

Support material is necessary in Fused Deposition Modeling (FDM) printing primarily when there are overhanging surfaces that exceed a specific angle from the vertical. Structures that have overhangs greater than 45 degrees from vertical begin to pose challenges during the printing process because they lack adequate support underneath. Without support, the extruded filament may sag or collapse as it is being laid down, leading to print failures and defects.

In contrast, while vertical surfaces and certain angles might not require support, anything beyond that critical threshold typically does. Printing with flexible materials does not inherently require support; the need for support is primarily influenced by the geometry of the model being printed. Lastly, while support can sometimes enhance surface finish in tricky spots, its main purpose is to ensure the integrity and stability of overhangs and complex geometries during the printing process. Thus, the requirement for support material is most accurately defined by the characteristics of overhanging surfaces.