The document discusses the science behind machining metal with cutting tools. It explains that cutting tools have rake and clearance angles that influence how metal chips are formed and removed. Rake angle in particular is a major control factor, as tilting the cutting edge changes how the chip is deformed and redirected. Microscope photos reveal the shear line where deformation occurs and the boundary zone of high heat and pressure near the cutting edge. Coolant application and other factors can influence the shear angle and heat generation. A deep understanding of tool geometry and chip formation physics is needed to control machining for better results.