What is the standard formula to calculate RPM for cutting speed?

The correct formula for calculating RPM (Revolutions Per Minute) based on cutting speed is derived from the relationship between linear speed, diameter of the tool or workpiece, and the number of revolutions. The standard formula is expressed as RPM = (SFPM × 12) / (π × Diameter), where SFPM is the surface feet per minute.

The option that states SFPM × 4 divided by Diameter rearranges the original relationship in such a way that it provides the correct calculation. This means that you take the cutting speed, multiply it by a constant (which takes into consideration unit conversion, in this case approximated as 4 for simplification), and divide by the diameter of the tool or workpiece to arrive at the revolutions per minute.

This option effectively positions SFPM as the linear speed that is then adjusted by the size of the cutting tool or workpiece, allowing the calculation to reflect how many times the tool must rotate to achieve the desired cutting speed on the material. Understanding this relationship is crucial for setting the correct RPM in CNC machining processes to ensure efficiency and precision in cutting operations.