Cutting tools are made of hard, rigid materials such as tungsten carbide and high-speed steel (HSS). Despite this, they do deflect ever so slightly when subjected to machining forces, a phenomenon that becomes increasingly troublesome the farther out the tool protrudes from the toolholder—depending on the operation, carbide cutters are good to a “stickout” of roughly four times the tool diameter, maybe a bit more on soft materials, while HSS tools become problematic at about half that distance. This leads to chatter (an ugly rippled surface), difficulty meeting part tolerances, and poor tool life. The lesson for a designer? Watch out for deep, narrow pockets, or part features situated alongside tall walls, lest cutter deflection create problems for those doing the machining.
