What is fillet used for?

Fillets appear as concave rounded edges for interior corners and as convex rounded edges for exterior corners. The rounded edges blend smoothly with the connecting surfaces in every direction, producing a seamless appearance.

Fillets are helpful in improving the mechanical properties of load-bearing parts produced by casting, machining, molding, and 3D printing. For casting, fillets help increase the manufacturability of cast parts because it helps in the removal of the part after molding. The smooth, rounded edges allow the part to easily slide out as opposed to sharp edges.

Fillets reduce stress concentrations in changes of section and direction on a part. They increase the part’s load-bearing capacity and fatigue life. Fillets accomplish this by distributing stresses over a larger area. Fillets are more effective than chamfers at reducing stress concentrations. This is because stress concentrations in chamfers are focused on the edges of the chamfer where the two surfaces meet. Beyond their mechanical benefits, fillets can improve the aesthetics of a part by removing the harsh appearance of sharp edges and corners.