Calculate CNC spindle RPM from cutting speed and tool diameter, compare RPM with a machine limit, and determine the actual cutting speed at the usable spindle speed.
Enter cutting speed and diameter to calculate spindle speed.
How do I calculate CNC spindle speed? Multiply cutting speed by 1000 and divide by π times tool diameter when using m/min and millimetres.
What is spindle RPM? RPM means revolutions per minute and describes how quickly the CNC spindle rotates.
Why does a smaller tool need higher RPM? For the same cutting speed, a smaller diameter travels a shorter distance per revolution, so more revolutions are required per minute.
Why does a larger tool need lower RPM? A larger tool travels farther around its circumference during every revolution, so fewer revolutions are required to achieve the same surface speed.
What is the difference between RPM and cutting speed? RPM measures rotational speed. Cutting speed measures the linear velocity at the cutting edge and depends on diameter as well as RPM.
Can this be used for CNC milling? Yes. Enter the milling cutter diameter and recommended cutting speed to calculate spindle RPM.
Can this be used for drilling? Yes. Enter the drill diameter and appropriate cutting speed for the material and drill geometry.
Can this be used for CNC turning? Yes. Enter the workpiece diameter and turning cutting speed. CNC constant-surface-speed modes may continuously adjust RPM as diameter changes.
What if the calculated RPM exceeds my spindle's maximum? The calculator reduces the usable RPM to the entered machine limit and reports the resulting actual cutting speed.
Should I always run at the maximum RPM? No. The correct RPM depends on the selected cutting speed, tool diameter, workpiece material, tooling and machining operation.
Why can actual recommended RPM differ from this calculator? Tool manufacturers may limit RPM because of cutter construction, balance, toolholder, stick-out, coating, machine capability or application-specific conditions.