Chamfers: a clean bottom edge without supports

What a chamfer is

A chamfer is a bevelled edge made by cutting off a corner with a flat face. It differs from a fillet in that the transition is not an arc but a straight sloping surface.

A chamfer is used to remove sharp edges, to make parts go together more easily and to simplify printing. For these reasons it is often more practical than a fillet in 3D printing.

Why it suits the bottom edge

If the bottom edge of a model is rounded, the base is an arc and the plastic sags on it. With a 45 degree chamfer each layer is shifted a little, but it sits firmly on the one below, so no support is needed and the edge comes out sharp.

A chamfer on the bottom edge also hides elephant foot, the slight widening of the first layer caused by nozzle pressure and bed heat.

Where else a chamfer helps

• Holes. A chamfered rim helps when inserting a screw or pin and hides small imperfections.
• Horizontal overhangs. A 45 degree slope turns an overhang into a self-supporting shape.
• Sharp edges. A chamfer of 0.5 to 1 mm takes off edges that catch on clothing.

What chamfer to design

With a 0.4 mm nozzle a chamfer of at least 0.6 to 1 mm makes sense, smaller ones get lost in the layers. On the bottom of a model, 1 to 2 mm is fine. Keep the angle around 45 degrees, with a steeper angle the supports come back.

When you export from a CAD program to STL or 3MF, a chamfer survives without any problem, because it is a flat surface.