What unit is typically used to measure spindle speed in CNC mills?

The unit used to measure spindle speed in CNC mills is revolutions per minute (RPM). This measurement indicates how many complete turns the spindle makes in one minute. Spindle speed is a critical parameter in CNC milling operations as it directly affects cutting performance, surface finish, and tool life.

When the spindle rotates, it drives the cutting tool, and the RPM must be optimized based on the material being machined, the tool's specifications, and the desired cutting speed. For example, higher RPMs can be advantageous for machining softer materials, while lower RPMs may be suitable for harder materials to avoid tool wear or failure.

The other units listed, such as inches per minute, millimeters per second, and feet per hour, are more related to feed rates, which measure the speed at which the workpiece moves through the cutting tool rather than the spindle itself. Understanding the distinction between these measurements is essential for effective machining and achieving the best results on a CNC mill.