KEVOS® MAKEOS · Threads
Lathe Threading Plan (Infeed per Pass, Spindle Speed and Time)
How should I split the thread depth into passes, what spindle speed can I use for this pitch, and how long will the thread take to cut?
Plan of single-point thread turning on a lathe: total radial depth for an external or internal 60° metric thread and constant-chip-area infeed per pass (as the thread infeed tool), spring passes, spindle speed from the cutting speed limited by the machine maximum and by the largest axial feed rate the machine can synchronise, the actual cutting speed, and cutting time for the passes over the thread length with run-in.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Thread | choice | External (on a shaft) or internal (in a bore) thread. |
| Major diameter | mm | Major (nominal) diameter. |
| Pitch | mm | Thread pitch. |
| Cutting passes | Number of cutting passes with infeed. | |
| Spring (zero-infeed) passes | Extra passes at full depth with no infeed, to clean up. | |
| Thread length | mm | Length of thread. |
| Run-in (acceleration) distance | mm | Distance before the thread for the axis to reach synchronised speed. |
| Cutting speed | m/min | Cutting speed for the insert and material. |
| Largest spindle speed | rpm | Highest spindle speed of the machine. |
| Largest axial feed rate while threading | mm/min | Highest axial feed rate the control can keep synchronised while threading. |
| Largest infeed per pass | mm | Largest radial infeed in one pass for the insert (your value). |
| Smallest infeed per pass | mm | Smallest infeed that still cuts rather than rubs (your value). |
Method and formulas
- Depth a_p = 0.6134P (external) or 0.5413P (internal); constant-area infeed: cumulative depth after pass x = a_p √(x − 1) ÷ √(n − 1), first pass a_p √0.3 ÷ √(n − 1) (as the thread infeed tool).
- Spindle speed n = min(1000 v_c ÷ π d, n_max, v_f,max ÷ P).
- Time = (passes + spring passes) × (L + run-in) ÷ (P n).
- Example: M20×2.5 needs 1.5335 mm depth; the first pass takes 0.31746 mm, the spindle runs at 1,591.5 rpm and the thread takes 4.7501 s.
Limitations
- Radial depth for basic 60° metric profiles; other forms and modified flank infeed differ.
- Rapid return moves between passes are not included in the time.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Program a threading cycle on a CNC lathe
- Check the first and last pass infeeds
- Estimate threading time for a quote
Who it is for
- CNC machinists
- Process planners
- CNC programmers
What you get
- Total depth and the infeed of each pass
- Spindle speed and what limits it
- Threading time
Interpreting the result
- Too many passes make the last infeed so small that the insert rubs; too few overload the first pass.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2037–2042, 1289–1300. Topic reference; no source tables or recommended settings are reproduced.
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Open the Lathe Threading Plan (Infeed per Pass, Spindle Speed and Time) calculator
