Question

A 31.8 MM HSS drill is used to drill a hole in cast iron block 100 mm thick at cutting speed of 20 m/min and feed 0.3 mm/rev. If the over travel of drill is 4 mm and approach 9 mm, the time required to drill the hole is

• A. 1 min 40 s
• B. 1 min 44 s
• C. 1 min 49 s
• D. 1 min 53 s

Answer 1

The correct option is D 1 min 53 s

Given data:
t = 100, D = 31.8 mm, $V_c$ = 20 m/min,

t = 0.3, OR = 4 mm, AP = 9 mm

$N=\frac{1000\times 20}{\pi \times 31.8}=200$

Break through distance,

$A{P}_1=\frac{1}{2}D=\frac{1}{2}\times 31.8=15.9$

$\text{Time/hole}=\frac{L}{f\times N}$

$=\frac{100+4+9}{0.3\times 200}$ =1.88 = 1 min. 53 sec.

Note: If we consider and calculate the
machining time, then there is no answer in the multiple choice.