Countersink for sheet metal circular holes - has oversize pilot hole drilled or punched and countersink produced by deforming hole edges

摘要

The method for countersinking round holes into metal parts, particularly metal parts of narrow width, first produces a pilot hole by boring or punching. The dia. of the pilot hole is greater than the nominal dia. of the final hole, but smaller than the max. size of the cone-shaped hole (3). A circular groove (6) is worked co-axial to the pilot hole and into the opposite face to that of the countersunk hole. The countersinking takes place by partial deformation of the metal in the pilot hole through punching. The stamping tools include a circular protrusion which is triangular-shaped and forms the groove.