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Request A ToolBasic Spindle Speed Calculator
Convert a known cutting speed into RPM using the effective cutting diameter. This is a rotation calculation, not a material recommendation. Enter cutter diameter for milling or drilling and workpiece diameter for conventional turning. Keep the diameter and source cutting-speed units visible when comparing two setups, especially if one tooling chart uses inches and the other uses millimetres.
Used For
Check cutting speed and the diameter at the cutting edge.
Formula
Metric: RPM = 1000 × Vc ÷ (π × D). Imperial: RPM = 12 × SFM ÷ (π × D).
Spindle Speed Basic
Enter the values you know. The result is calculated in your browser.
Calculation only. Verify toolmaker data, material grade, engagement, machine limits, workholding and actual cutting conditions before production.
Advanced Spindle Speed Calculator
Review the additional variables shown in this tool.
Spindle Speed
Enter the values you know. The result is calculated in your browser.
Calculation only. Verify toolmaker data, material grade, engagement, machine limits, workholding and actual cutting conditions before production.
Convert Surface Speed To Spindle RPM
- Choose the unit mode that matches the cutting-speed source.
- Enter cutting speed and the cutting diameter. For conventional turning, enter workpiece diameter at the cut.
- Calculate the theoretical RPM. In the advanced panel, enter the machine ceiling to compare capped RPM and its resulting surface speed.
Formula And Units
Metric: RPM = 1000 × Vc ÷ (π × D). Imperial: RPM = 12 × SFM ÷ (π × D).
Illustrative Calculation
An illustrative cutting speed of 100 m/min and diameter of 10 mm give 3,183 RPM. At 20 mm, the same cutting speed gives 1,592 RPM. Doubling diameter halves RPM when cutting speed is held constant.
Use The Diameter At The Cut
The shank diameter is not always the cutting diameter. For a rotating workpiece, a change in machined diameter changes the relationship between RPM and surface speed. Check which diameter the toolmaker formula expects.
When The Machine Cannot Reach The Result
A spindle ceiling changes actual cutting speed. With 10 mm diameter and a 2,000 RPM ceiling, actual speed is about 62.8 m/min. Check whether that condition is appropriate rather than treating the cap as a machining recommendation.
Check the formula reference or report a result that does not match your calculation.
Calculation Process With Example Values
Illustrative arithmetic only. Select cutting inputs from the applicable tool and material reference.
| Step | Substitution | Result |
|---|---|---|
| RPM | 1000 × 100 ÷ (π × 10) | 3,183.10 RPM |
A Diameter Error Carries Into RPM
RPM varies inversely with diameter. Entering a shank diameter where an effective cutting diameter is required changes the result even when the surface-speed input is correct. Keep full precision until the final RPM is chosen. The reverse cutting-speed calculation can check the surface speed at that command.
Formula reference: Sandvik Coromant milling formulas and definitions. Use the exact tool supplier for recommended cutting values.
Applications And Related Calculation Workflows
RPM For Milling, Drilling And Turning
RPM and spindle speed name the same rotational quantity in this calculation. A milling spindle speed calculation uses the cutter diameter; drilling uses drill cutting diameter. On a conventional lathe, use workpiece diameter at the cut. The CNC spindle speed formula remains a cutting-speed-to-diameter conversion rather than a decision about which cutting speed is suitable.
Theoretical RPM And A Machine Limit
Check whether the calculated spindle speed is available on the actual machine. If a limit reduces RPM, calculate the resulting surface speed with the cutting speed calculator. For milling, recalculate linear feed from the actual RPM if you intend to preserve nominal feed per tooth. A numerical ceiling does not establish a suitable cutting condition.
Spindle Speed Questions
Is An RPM Calculator Different From A Spindle Speed Calculator?
In this calculation they describe the same result (revolutions per minute). Surface speed and diameter are the inputs. Feed rate is a separate quantity.
What Happens If The Spindle Is Slower Than The Result?
The actual surface speed is lower. The advanced panel shows that surface speed at the entered ceiling. Revisit the tool data and, for milling, recalculate feed using actual RPM.
Help Improve This Resource
Report An Error
Share this page address, the entered values and the result you expected. Include the source of your comparison so the formula, units and explanation can be investigated.
Report An ErrorCNC Feeds & Speeds Editorial Desk
The site brings calculation tools and machining references into one workspace. Use the editorial and site information to understand its purpose and limitations. Send corrections with a reproducible example through the error report form.
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