Here are very useful calculators from custompart.net
Milling Speed and Feed Calculator
Determine the spindle speed (RPM) and feed rate (IPM) for a milling operation, as well as the cut time for a given cut length. Milling operations remove material by feeding a workpiece into a rotating cutting tool with sharp teeth, such as an end mill or face mill. Calculations use the desired tool diameter, number of teeth, cutting speed, and cutting feed, which should be chosen based on the specific cutting conditions, including the workpiece material and tool material. Learn more about Milling.
Milling Speed and Feed Calculator
Calculate the horsepower required for a milling operation based on the feed rate and depth of cut, which are used to determine the material removal rate (or metal removal rate). Also required is the unit power, which is a material property describing the amount of power required to cut that material. The horsepower at both the spindle and the motor are shown, as well as the spindle torque for a given spindle speed (RPM). The motor horsepower required for the milling operation can then be compared to the horsepower capability of the machine. Learn more about Milling.
Milling Step-over Distance Calculator
In many milling operations, the cutting tool must step over and make several adjacent cuts to complete machining a feature. As a result, a small cusp of material, called a scallop, will remain between these cuts on any surrounding walls or on the machined surface if a ball end mill is used. The size of the step-over distance and the tool diameter will determine the scallop height between each step. Decreasing the step-over distance will minimize the scallop height, but will require more steps, and therefore more time, to machine the feature. Learn more about Milling.
Milling Step-over Distance Calculator