Drill Sharpening
P&N drills are pointed on precision automatic grinding machines. The standard point geometry on P&N drills has an included angle of 118° with a lip relief angle of 12° to 15° .This drill is suitable for most materials. However, a user will sometimes find it necessary to repoint the drill to better suit the material being machined.
Web Thinning
Most P&N drills have a web that is thin near the point of the drill. As a drill is resharpened it becomes shorter, the web thickness becomes greater and the drill point develops a much longer chisel edge. This longer chisel edge will result in more pressure being required for penetration, resulting in greater heat generation and a reduction in drill life. The chisel edge can be reduced by web thinning.
For correct web thinning it is important that equal amounts of material be ground from either side of the chisel edge until the total length of the edge returns to the same value as that found on a new drill. (Excessive web thinning weakens the point of the drill and splitting of the web may occur.)
The ground surface produced by web thinning must blend evenly into the flutes without abrupt termination. The web thinning should extend 50 to 100% of the drill diameter along the flute.
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