A schematic diagram of peripheral milling is shown in the Figure.

If $$t$$ is the depth of cut and $$d$$ is the diameter of the milling cutter, then the length of approach $$\left( {la} \right)$$ is expressed as

Turning, drilling, boring and milling are commonly used machining operations. Among these, the operation (s) performed by a single point cutting tool is (are)

The Merchant circle diagram showing various forces associated with a cutting process using a wedge shaped tool is given in the Figure

The coefficient of friction can be estimated from the ratio

In a machining operation with turning tool, the tool life $$(T)$$ is related to cutting speed $$v$$ $$(m/s),$$ feed $$f(mm)$$ and depth of cut $$d(mm)$$ as $$$T = C\,v{\,^{ - 2.5}}\,{f^{ - 0.9}}\,{d^{ - 0.15}}$$$
where, $$C$$ is a constant. The suggested values for the cutting parameters are: $$V=1.5$$ $$m/s,$$ $$f=0.25$$ $$mm$$ and $$d=3$$ $$mm$$ for normal rough turning. If the operation is performed at twice the cutting speed and the other parameters remain unchanged, the corresponding percentage change in tool life is ______________.