If a bar of SAE 1040 is to be turned with a high speed steel tool with a feed of 0.015" per revolution, and a depth of 0.050". Previous experiments have revealed that the following cutting velocities yielded the following tool lives,
90 fpm for 30 min.
80 fpm for 90 min.
75 fpm for 150 min.
a) estimate the cutting speeds to get tool lives of 60 and 120 minutes.
b) calculate the mrr at the two speeds found in part a).