Question

A hole of $20mm$ diameter is to be drilled in a steel block of $40mm$ thickness. The drilling is performed at rotational speed of $400rpm$ and feed rate of $0.1mm/rev$. The required approach and over run of the drill together is equal to the radius of the drill. The drilling time (in minute) is

• A. $1.00$
• B. $1.25$
• C. $1.50$
• D. $1.75$

Answer 1

The correct option is B $1.25$

$\text{Drilling time: t}=\frac{L}{fN}$

$L=$ thickness $+$ Approach $+$ Overrun
$=40+10=50mm$

$f=0.1mm/rev$
$N=400rpm$

Drilling time
$\therefore t=\frac{50}{0.1\times 400}=\frac{500}{400}=1.25min$