Question

A drilling operation is performed on a steel part using a 12.7 mm diameter twist drill with a point angle of 118 degrees. The hole is a blind hole with a depth of 50 mm. Cutting speed=15 m/min, and feed=0.20 mm/rev.
Determine the following:

a. Rotational speed of the drill
b. Feed rate
c. Approach allowance
d. Cutting time
e. Metal removal rate after the drill bit reaches full diameter.

Answer 1

Answer:

a. Rotational speed of the drill  = 375.96 rev/min

b. Feed rate  = 75 mm/min

c. Approach allowance  = 3.815 mm

d. Cutting time  = 0.67 minutes

e. Metal removal rate after the drill bit reaches full diameter. = 9525 mm³/min

Explanation:

Here we have

a. N = v/(πD) = 15/(0.0127·π) = 375.96 rev/min

b. Feed rate = fr = Nf = 375.96 × 0.2 = 75 mm/min

c. Approach allowance = tan 118/2 = (12.7/2)/tan 118/2 = 3.815 mm

d. Approach allowance T∞ =L/fr = 50/75 = 0.67 minutes

e. R = 0.25πD²fr = 9525 mm³/min.