A machinist who knows a machine tool's maximum level of productivity can run the machine at its highest-capable speeds and feeds without stalling it. To help determine the maximum productivity when turning, I developed the methodology and supervised the testing of 20 workpiece materials. Based on these test results, five equations were developed to generate actual numbers that represent the workpiece material for various machining conditions with different cutting parameters.Traditionally, machining power when turning is estimated through the metal-removal rate multiplied by the power constant of a workpiece material (also known as the "p-factor"). The method is simple, but not accurate. The reason is that the power constant of any work-piece depends on many variables, including the microstructure and hardness of the work material, cutting tool geometry, sharpness of the cutting edge, depth of cut and feed rate. This explains why power-constant values are usually overestimated, sometimes by more than 40 percent. This overestimating results in lost productivity, since the machine isn't operated at its highest speeds and feeds.
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