Regrinding the point of the twist drill bits

After removing the worn areas of the drill, the surfaces of the point must be reground.

The two cone-shaped surfaces intersect the faces of the flutes to form the cutting lips. They also form the chisel edge where they intersect with each other in the center.

Similar to other cutting tools, the surface of the cutting lip of the twist drill bits must not rub against the work, but must be relieved to allow the edge to penetrate. Without such relief the drill would not penetrate, and would only rub against the surface.

This clearance is called lip relief. The lip relief angle of the twist drill bits is measured at the outer edge of the drill bits in order to obtain the correct chisel-edge angle.

Point grinding by hand involives great care and skill on the part of the operator.

In order ot achieve accurate point angles, lip angles, and chisel-edge angles, a point grinder is recommended.

It is essential that the two cutting edges be exactly the same length and have the same slope to the axis.

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