Question

A $\varphi -20mm$ through hole is to be drilled in a $30mm$ thick plate using a double fluted, ${120}^o$ lip angle drill. The drill tip is at a distance of $3mm$ from the plate surface when cutting is started and an overtravel of $2mm$ is recommended as a margin to ensure drilling through the full thickness of the plate. If the drill rotates at $500rev/mn$ and the feed per tooth is $0.01mm$, the machining time of the operation (in $min$) will be

• A. $4.5$
• B. $7.5$
• C. $9$
• D. $10.5$

Answer 1

The correct option is A $4.5$

Given data:
$D=20mm,t=30mm$

Double fluted
$AP=3mm$
$OR=2mm$
$N=500rpm$

Feed/tooth $=0.01mm$
$L=30+3+2+0.25\times 20=45mm$
$f=0.01\times 2=0.02mm$

Machining time
$=\frac{L}{f\times N}=\frac{45}{0.02\times 500}=4.5min$