In such a way, when the bore tip is worn by use, said tip can be recoated after sharpening without the nominal diameter of the drill tip substantially increasing, in particular even after being sharpened several times.

Accordingly, even though no oil hole is formed in a drill through a complicated manufacturing process, it is possible to stably supply the cutting oil to the point of the drill.

The concave or hollow surface of the drill tip allows nails or skin tissue to be drilled and channeled away from the point of drilling for reducing the difficulty, and pain of the procedure.

A keyed bearing (20) can be installed inside a sleeve (30) of the ram (9) in order to protect the tip of the masonry drill bit from shearing.

These calibrated depressions (11) give a visible indication of when the tip or point of the drill is at the full length of depth of a drilled hole.

The twist drill bits of the invention comprise a layer of abrasive compact of substantially uniform axial thickness extending over substantially the whole top surface of the tip of the drill bit.

In this arrangement, the centre line (X) of the shank intersects with the centre line (Z) of the head at the countersink point.

The procedure in this steps will heat the drill bit’s face up, so getting a cup of cold water readily available by your side to dip the tip of the drill bit into is advisable to cool it off.

Usually, in modern mines, the dust is prevented by a continuous stream of water directed out of the drill tip.

The drill bit can be re-ground or fitted with new screw-cutting plates or replaced after use with a new plate by simply releasing the positive-fit mount.

Another way of finding problems is to again visually examine the drill-bit, looking especially at the clearance angles.

Usually, the point angle of twist drill bit is about 118°，it could also be treated 120°, the sharpening skills as follows:

The invention proposes that the cutting edges (2) should be aligned symmetrically about the drill bit axis and the cutting edges should be in cutting engagement over the entire radius of the bore to be drilled.