Drilling small-dia bore in solid metal - involves short drill with unequal cutting portions of specified geometry integral with hard metal shank

摘要

The short drill is intended for drilling a bore in solid metal and comprises two, pref. hard-metal, cutting portions (3,4) of unequal length whose chip clearance faces extend approximately radially relative to the drill axis (7). Each portion (3,4) has forwardly converging end faces. (9) and (11) are the inner faces of the respective portions. They meet at an obtuse angle forming a cutting point. These two points are at the same radial distance from the axis (7) and nearer to this axis than to the periphery (19) of the drill. The longer portion (3) extends radially inward to or slightly beyond (as shown) the centre (7) whilst the shorter portion (4) does not extend as far as the centre. The portions (3,4) are preferably integral parts of the drill.