Controlled and Uncontrolled Separation of Parts: Cutting, Scraping and Spreading

This chapter provides an introduction to cutting, scraping, and spreading and discusses the tools employed to accomplish these tasks. A characteristic feature of some of the controlled cutting is that the cutting tool or blade is not deformed when cutting, and remains ready for reuse. The only significant deterioration may be wear and blunting; unless corrected, the quality of the cut deteriorates. An issue that needs to be addressed to ensure effective cutting is how hard a tool should be to avoid itself being deformed in cutting. Mutual cutting is possible where both tool and workpiece deform (bullets and the target). When it is difficult to insert a woodscrew, the high torque will distort the blade of a poor-quality screwdriver and also cut slivers from the side of the slot in the head of the screw. Many tools can be resharpened and used again. Sometimes tools are used once only (disposable scalpels) or thrown away when blunt (disposable razors, or indexable tool inserts). Hollow needles that pierce the skin and through which liquids may be inserted into the body (hypodermics) or removed (cannulae) may sometimes be reused depending on conditions. Improvements in tool material qualities, and reductions in cost, mean that it is often uneconomic to resharpen tools.