“Most 3D printable parts are designed to limit overhangs to 45 degrees or less. That’s because maker-style 3D printers (technically FDM) build each layer from the bottom up, fusing the current layer onto the previous, and if there’s nothing below a layer, the plastic will sag (or worse yet, form a glob and potentially ruin your part).
To get around the overhang limit, parts are often significantly modified (with chamfers to reduce overhangs) or support material is used to hold up sections that extend too far. But neither approach works all the time; sometimes you can’t chamfer away the overhangs and/or rely on support material to bail you out.”