Page 99 - CITS - Fitter Trade Pactical - Volume - 2

FITTER - CITS

Also note that, if the drill is twisted too far, the other cutting edge will swing down to contact the wheel face.

Proceed now to sharpen one edge, removing as little metal as possible.
Procedure to obtain equal angles
Move the drill back, clear of the wheel face.
Turn the drill over without moving the position. This presents the second edge to the wheel face at the same angle
as the first cutting edge.
Proceed to sharpen the second cutting edge, using the same amount of drill movement as before. When these
actions are carried but carefully, the drill will be sharpened with equal cutting angles. The lip clearance will be
correct and equal.
Use a drill angle gauge to check that the cutting angle is correct (118° for mild steel), the cutting edges are of
equal length and the lip clearances are equal and correct (about 12°). (Fig 6)

Fig 6

Lift the drill off the wheel face. Retain the grip on the drill with the right hand.
Make such inspection or checks as are necessary. Move the right hand back on-the tool-rest in the same position
as before.

Hold the drill shank again in the left hand with the elbows against the side. The drill will locate back against the
wheel face in the same position and at the same angle as before.
Points to be considered when sharpening drills

Grind as little as possible from the drill. Remove only enough to sharpen the cutting edges.
Rough down the drill point with a coarse grit wheel when the edges are badly chipped.(Fig 7)

Fig 7

Never re-sharpen a cracked or split drill. Avoid overheating the drill.

Apply light pressure against the wheel face. Lift the edge clear of the wheel face frequently. This allows the air
stream produced by the wheel to cool the drill point.(Fig 8)

84

CITS : CG & M - Fitter - Exercise 29