Question

In a shaping operation, the average cutting speed is ( Stroke length S, Number of strokes per minute N, Quick return ratio R)

(a) NSR

(b) NSR/2

(c) NS(1 + R)

(d) NS(1 + R)/2

This question was addressed to me by my school principal while I was bunking the class.

Origin of the question is Types of Kinematic Chains in section Simple Mechanisms of Machine Kinematics

Answer 1

Correct answer is (d) NS(1 + R)/2

The explanation: Time for forward stroke + Tf

Time for return stroke = Tr

R = Tr/Tf

Therefore, time for only one cutting stroke(T) = 1/N x Tf/(Tf + Tr)

Average cutting speed = S/T = SN(Tf + Tr)/Tf = SN(1 + R).