Reviewed and updated September 12, 2026
Four terms to separate
| Term | Common metric unit | Meaning |
|---|---|---|
| Cutting speed (Vc) | m/min | Speed at the cutting edge relative to the workpiece |
| Spindle speed (n) | rev/min (RPM) | Rotational speed of tool or workpiece |
| Feed per tooth (fz) | mm/tooth | Advance assigned to each engaged cutting edge |
| Feed rate (Vf) | mm/min | Linear advance of the tool relative to the workpiece |
Useful metric relationships
Vf = n × z × fz
Here, D is cutter or workpiece diameter in millimetres and z is the number of effective cutting edges. In inch-based shops, surface speed is often expressed in surface feet per minute (SFM) and feed in inches per tooth or inches per revolution. Do not mix unit systems inside a calculation.
Why published values are starting points
Toolmaker data assumes a defined insert or cutter, material group and engagement. A real setup also has machine-power limits, spindle characteristics, holder runout, tool overhang, workholding stiffness, coolant conditions and surface-finish goals. Turning research likewise shows that cutting speed, feed and depth of cut interact with force, temperature, roughness and tool wear.
Read the process, not only the calculator
| Observed symptom | Possible contributors to investigate |
|---|---|
| Chatter or repeating marks | Rigidity, tool overhang, engagement, spindle speed, workholding |
| Poor finish | Runout, worn edge, built-up edge, feed, vibration, tool geometry |
| Rapid tool wear | Excess heat, inappropriate speed, coating/material mismatch, poor chip evacuation |
| Rubbing rather than cutting | Feed too low, dull edge, deflection or runout |
These are diagnostic prompts, not automatic remedies. Change one controlled variable at a time and verify toolmaker guidance.
What designers should take from this
- Deep narrow pockets may force long-reach tools and conservative parameters.
- Very small corner radii can require smaller cutters and more passes.
- Thin walls can deflect as cutting force changes.
- Interrupted cuts and poor chip evacuation affect stability.
- Material condition can matter as much as the alloy name.