Why do historians continue to gather historical evidence for even well-known events? They want to find artifacts to sell.
They are looking for evidence to predict the future.
They know that new evidence may lead to new interpretations.
They assume that new technology will prove all of the old theories incorrect.

Aturning operation is performed with following conditions: rake angle of 12°, a feed of 0.35 mm/rev, and a depth of cut of 1.1 mm. the work piece is aluminum alloy 6061 with t6 heat treatment (a16061-t6). the resultant chip thickness was measured to be 1.0 mm. estimate the cutting force, fc. use shear stress of 207 mpa and coefficient of friction on the tool face of 0.6.