AiVibeSpindle Speed (RPM)
Spindle speed is the rotational speed of the machine spindle in revolutions per minute, set in a CNC program by the S word. It is calculated from the recommended cutting speed and the tool or workpiece diameter.
For a given cutting speed Vc in metres per minute and a diameter D in millimetres, spindle speed n in rev/min is n = 1000 Vc / (pi D). In milling D is the tool diameter; in turning it is the workpiece diameter at the cutting point. The program sets speed with the S word and starts the spindle with an M-code. Lathes often use constant surface speed, which adjusts rev/min continuously as the diameter changes, with a programmed upper limit.
Correct spindle speed keeps the cutting edge at the speed the tool supplier recommends for the workpiece material, which balances productivity, tool life and surface finish. Small tools need high spindle speeds to reach their recommended cutting speed, which is one reason high-speed spindles are used for small-tool and mould work.
Usable speed is limited by the machine's maximum, the rating and balance of the tool holder and tool, the limits of chucks and workholding, and available power and torque at that speed. Some speeds excite chatter while others are stable, and stability lobe diagrams can help select them. Operators can scale speed with the spindle override, but persistent overrides indicate the programmed data should be reviewed.
Key points
- Spindle speed n = 1000 Vc / (pi D) with Vc in m/min and D in mm
- Set in the program with the S word
- Constant surface speed on lathes needs an upper speed limit
- Limited by machine, holder, tool and workholding ratings
Where AiVibe comes in
AiVibe designs and manufactures the AiAmbA AI Factory: edge devices plus AI agents that let people talk to CNC, PLC and robot controllers in plain language. Agents only propose changes, and a trained operator confirms each one.
Related terms
- Cutting Speed (Surface Speed, Vc)CNC & Precision Machining
- Feed RateCNC & Precision Machining
- Machine Tool SpindleCNC & Precision Machining
- Chip Load (Feed per Tooth, fz)CNC & Precision Machining
- Stability Lobe DiagramCNC & Precision Machining