Consider the corners of a machined pocket—the inside of an electronics housing, perhaps, or a bracket used to capture the body of a rectangular component. One common design oversight is leaving the intersection of the vertical walls on those part features perfectly sharp. To illustrate, think about machining a stainless steel box to hold a collection of baseball trading cards. The only way to get the perfectly square corners needed to fit those Babe Ruths and Hank Aarons is with electrical discharge machining (EDM), a slow and expensive process.
Instead, we'll equip one of our machining centers with the smallest end mill available to clean out the corners. In 304 stainless steel, that means a 0.031 in. (0.8mm) end mill, which leaves a corner radius of 0.016 in. (0.4mm). That's pretty sharp, but the depth is limited. The length of most steel-cutting end mills in this size range maxes out at five times the cutter diameter, barely deep enough to fit your favorite center fielders. Machining with small end mills such as this is also slow and delicate work, driving up the cost of your project.