Fillet (mechanics)

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In mechanical engineering, a fillet (pronounced /ˈfɪlɪt/, like "fill it") is a rounding of an interior or exterior corner of a part. An interior or exterior corner, with an angle or type of bevel, is called a "chamfer". Fillet geometry, when on an interior corner is a line of concave function, whereas a fillet on an exterior corner is a line of convex function (in these cases, fillets are typically referred to as rounds). Fillets commonly appear on welded, soldered, or brazed joints.

Depending on a geometric modelling kernel different CAD software products may provide different fillet functionality. Usually fillets can be quickly designed onto parts using 3D solid modeling engineering by picking edges of interest and invoking the function. Smooth edges connecting two simple flat features are generally simple for a computer to create and fast for a human user to specify. Once these features are included in the CAD design of a part, they are often manufactured automatically using computer-numerical control.