During orthogonal cutting of mild steel with a $$10$$ degrees rake angle tool the chip thickness ratio was obtained as $$0.4.$$ The shear angle (in degrees) evaluated from this data is

For turning $$NiCr$$ alloy steel at cutting speeds of $$64m/min$$ and $$100m/min,$$ the respective tool lives are $$15min$$ and $$12$$ $$min.$$ The tool life for a cutting speed of $$144m/min$$ is

A conventional lathe and a $$CNC$$ lathe are under consideration for machining a given part. The relevant data are shown below :

The machine preferred for producing $$100$$ pieces is

What is the approximate $$\% $$ change in the life, $$t,$$ of the tool with zero rake angle used in orthogonal cutting when its clearance angle, $$\alpha ,$$ is changed from $$10$$ to $$7$$ deg?

(Hint: flank wear rate is proportional to $$\cot \,\alpha $$)