broach(redirected from brooch)
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a metalcutting tool with multiple blades used on broaching machines to machine outer surfaces and through-holes. The following broaches are distinguished, based on the shape of the surface to be worked: cylinder, faceted (square, hexagonal, and so forth), spline, keyway, flat surface, and shaped surface broaches.
In broaches used for internal broaching (Figure 1, a), the teeth are arranged on a tapered cutting section; they carry out the major work of cutting the final layer of stock to size. The finishing section of the broach has from three to eight teeth. The first of these cut a very thin layer of metal and give the hole its final shape; the other teeth are spares and are used after the broach is reground. Broaches for external broaching (Figure 1, b) are manufactured in the shape of a rectangular bar and have cutting and finishing sections.
In addition to cutting broaches, there are burnishing broaches, which do not cut, but rather smooth and flatten metal. The flattened layer produced by such broaches has high resistance to wear. The teeth of burnishing broaches do not have cutting angles; they are sometimes positioned on the finishing section of the broach.