Read: Twist Drill Nomenclature/ Parts of a Twist Drill
The geometry and sharpening of the tool are crucial in the performance of twist drill. The special tool grinders are available for sharpening and reshaping of tools cutting edge.
The various angles of twist drill are given below
Rake angle/helix angleIt is the angle of the flute in relation to the work surface. The value of rake angle varies between 18° to 45°; its typical value is 30°.
The rake angle governs the tightness with which chip curls and hence the amount of space occupied by the chip. The higher rake angle cause tightly rolled chip while the small rake angle tends to chip curl into more loosely rolled helix. Large rake angle causes excessive vibration and chatter of drill.