Spindle RPM is derived from cutting speed and cutter diameter. Table feed is then derived from feed per tooth Ă— RPM Ă— number of effective cutting teeth.
Four quantities you should keep separate
- Cutting speed (vc): surface speed at the cutting edge, usually m/min.
- Spindle speed (n): revolutions per minute.
- Feed per tooth (fz): chip load per effective cutting edge.
- Table feed (vf): programmed feed rate, usually mm/min.
Example
If a 10 mm end mill is to run at 120 m/min, the calculated spindle speed is approximately 3820 rpm. With a 4-flute cutter and 0.04 mm/tooth chip load, table feed is approximately 611 mm/min.
Why copying someone else’s RPM can fail
The correct cutting condition depends on workpiece material, hardness, cutter grade/coating, diameter, radial/axial engagement, rigidity, coolant strategy and machine limits. Use the cutting-tool supplier’s recommended starting range and adapt using measured tool life and part quality.
Signs that the process needs review
- Chatter or vibration.
- Rapid flank wear/chipping.
- Built-up edge.
- Excessive spindle load.
- Poor finish or dimensional drift.
- Chips that are powdery, blue/overheated or not evacuating.
Shop-floor discipline
Record the tool, holder, stick-out, material, operation, vc/fz, depth/width of cut and result. A repeatable process sheet is more valuable than a single “magic RPM”.
This article is general guidance for preliminary engineering and shop-floor understanding. The drawing, applicable standard, machine/tooling OEM instructions, process-specific safety requirements and qualified engineering judgment take priority.