14.75 mm

14.50 mm

15.25 mm

14.65 mm

Drill is not sharp

Unequal lip length

Feed rate is too high

Cooling is insufficient

Drilling

Spot facing

Countersinking

Counterboring

To drive out the chips

To reduce the weight

To reduce the cost

To increase the speed

75 Degree

80 Degree

90 Degree

120 Degree