When working with different metals and various machining operations, it is important to be able to calculate working speeds and feeds on the fly. These two most important parameters relate directly to surface finish, efficiency, and tool life. Most people just starting to get comfortable in the machine shop are establishing familiarity with the operation large machines. As they become less interested in the operation of the machine itself their attention is turned to workpiece. The question of 'how fast?' is suddenly of great importance.
Experience will eventually replace nearly all habits of returning to reference tables or blind guesses. In the meanwhile, or when a particular speed/feed is called to question, their are some general rules of thumb which can be used with great success to establish starting points for speeds and feeds. On a manual mill, the speed (rpm) is usually needed, while feedrates are established by feedback sensed by the operator through the handwheels. On a manual lathe, both speed and feed are useful to know. And of course, if programming for a CNC mill or lathe, both of these parameters are determined beforehand and to great benefit if done with any degree of accuracy.
Because these 'rules of thumb' are often hard to come by, I have compiled them here as a reference to anyone in need. I believe that this first document is more for the newcomer and student, but should be useful as an educational tool as well: