BIZOMAT MAKEOS · Manufacturing
Cutting Speed and Spindle RPM
What RPM corresponds to the chosen cutting speed?
Convert a specified surface speed to spindle RPM, and check the surface speed at an actual machine setting.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Effective cutting diameter | mm | Tool supplier geometry at the actual cutting depth; work diameter for turning. |
| Specified cutting speed | m/min | Validated tooling data for the material, grade, operation and setup. |
| Spindle speed | rpm | Actual machine setting, checked against tooling and machine limits. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Effective cutting diameter
- What it is
- The diameter at which the cutting edge actually cuts: the tool diameter for drilling and milling, or the workpiece diameter at the cut for turning.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.001 mm to 1000000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Required rpm is inversely proportional to diameter; actual surface speed is directly proportional to it.
- Get it right
- For ball-nose or chamfer tools the effective diameter at the cutting depth is smaller than the nominal size.
What this means: Specified cutting speed
- What it is
- The surface speed at which the cutting edge should pass the material, from validated tooling data for this material, tool grade and operation.
- Units and format
- Enter a number in m/min: metres per minute. The form accepts 0.001 m/min to 1000000 m/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 120 m/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Required spindle rpm is directly proportional to the specified cutting speed.
- Get it right
- This is metres per minute at the cutting edge, not spindle rpm; the tool converts it.
What this means: Spindle speed
- What it is
- The spindle speed actually set on the machine, used to check what surface speed you are really running at this diameter.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.001 rpm to 1000000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1000 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Actual surface speed is directly proportional to spindle speed.
- Get it right
- It only affects the actual surface speed check, not the required rpm result.
Method and formulas
- Required RPM = 1000 × cutting speed ÷ (π × diameter).
- Actual surface speed = π × diameter × actual RPM ÷ 1000.
- Example: 20 mm at 120 m/min requires 1909.859 rpm. At 1000 rpm the speed is 62.832 m/min.
Limitations
- The input speed is supplied by you; this tool does not select cutting data.
- Effective diameter can differ from nominal diameter for ball-nose and round-insert cutters.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- spindle speed
- surface speed
- SFM planning
Who it is for
- Machinists
- Manufacturing engineers
What you get
- Required spindle speed
- Actual surface speed
Interpreting the result
- Choose an available RPM and check tool, spindle and workholding speed ratings.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1013–1017. Topic reference; no source tables or recommended settings are reproduced.
- Sandvik Coromant: Milling formulas and definitions — https://www.sandvik.coromant.com/en-gb/knowledge/machining-formulas-definitions/milling-formulas-definitions
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