Twist drills
AssigneeOsborn-Mushet Tools Limited
InventorKeith Siddall
Life of this patent
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Abstract
A twist drill the cross-sectional shape of which is such that, although it can be sharpened on a conventional machine so that its cutting edges are contained in the surface of an imaginary cone, its cutting edges are curved and their lip rake is substantially constant radially outwards of the drill core.
Claims6
A twist drill having a cross-sectional shape which is convex in the surfaces of the drill faces, the convexity being of such an extent that it conforms substantially to a radius of between 0.9 and 1.2 of the drill radius, the lip rake angle being substantially constant along the cutting edges radially outwards of the core portion of the drill, the helix angle being between 25.degree. and 45.degree., and the point angle being between 90.degree. and 150.degree., whereby the cutting edges are curved but contained in the surface of an imaginary cone so that the drill can be sharpened on a conventional machine.
Dependencies are inferred from the claim text.