Question

Through holes of $10mm$ thickness. Drill spindle speed is $300rpm$, feed $0.2mm/rev$ and drill point angle is ${120}^o$. Assuming drill overtravel of $2mm$ the time for producing a hole will be

• A. $4$ seconds
• B. $25$ seconds
• C. $100$ seconds
• D. $110$ seconds

Answer 1

The correct option is B $25$ seconds

Given data:
Diameter of hole,

$d=10mm$

thickness of steel plate,

$t=20,mm$

$\alpha =\frac{120}{2}={60}^o$

Break through distance,

$A=\frac{d}{2tan\alpha }=\frac{10}{2tan{60}^o}$

$=2.8867mm$

Total length of tool travel,

$l=t+A+2$

$=20+2.8867+2=24.88mm$

$\text{Time for drilling}=\frac{l}{f\times N}$

$\frac{24.88}{0.2\times 300}=0.4147min$

$=0.4147\times 60s$

$=24.882s=25s$