BIZOMAT 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). |
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: Thread
- What it is
- Whether the thread is cut on the outside of a shaft or inside a bore. It sets the total radial depth of the thread profile.
- Units and format
- Choose one of 2 options from the list: External; Internal.
- Example
- The form opens with “External” selected as a worked example. Choose the option that matches your case.
- Get it right
- An internal thread has a smaller basic depth than an external thread of the same pitch.
What this means: Major diameter
- What it is
- The major (nominal) diameter of the thread, used with the cutting speed to find the spindle speed.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 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
- At the same cutting speed, a larger diameter means a lower spindle speed and a longer time.
- Get it right
- Use the nominal size, for example 20 for M20, for both internal and external threads.
What this means: Pitch
- What it is
- The distance from one thread crest to the next along the axis, which is also how far the tool moves per spindle revolution.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 20 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2.5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger pitch makes the thread deeper and raises the axial feed rate.
- Get it right
- For an inch thread, pitch = 25.4 ÷ threads per inch.
What this means: Cutting passes
- What it is
- The number of passes with infeed that cut the thread to full depth. The infeed is shared so each pass removes about the same chip area.
- Units and format
- Enter a plain number with no unit. The form accepts 2 to 60. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More passes make each infeed smaller, especially the first.
- Get it right
- Count only passes with infeed; zero-infeed spring passes have their own input.
What this means: Spring (zero-infeed) passes
- What it is
- Extra passes at full depth with no further infeed, to clean up the flanks and remove spring-back.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 10. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Each spring pass adds one pass to the threading time.
- Get it right
- These add time but no depth; use 0 if you do not take spring passes.
What this means: Thread length
- What it is
- The length of the threaded portion along the axis, the distance the tool cuts on each pass.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 5000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Threading time rises with length.
- Get it right
- Use the full thread length on the drawing, without the run-in.
What this means: Run-in (acceleration) distance
- What it is
- The distance the tool starts before the thread, so the axis can reach synchronised feed before it begins cutting.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 200 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- It adds to every pass, so it lengthens the time.
- Get it right
- The tool warns if the run-in is shorter than three pitches.
What this means: Cutting speed
- What it is
- The cutting speed at the major diameter recommended for the insert grade and work material.
- Units and format
- Enter a number in m/min: metres per minute. The form accepts 0.000001 m/min to 500 m/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 m/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher cutting speed raises the spindle speed until a machine limit takes over.
- Get it right
- Take it from the insert maker for threading, which is usually lower than for turning.
What this means: Largest spindle speed
- What it is
- The highest spindle speed the lathe allows, which can cap the speed set by the cutting speed.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 100000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3000 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Include any chuck or workholding speed limit, which may be below the spindle limit.
What this means: Largest axial feed rate while threading
- What it is
- The highest axial feed rate the control can keep synchronised with the spindle while threading. It can cap the spindle speed on coarse pitches.
- Units and format
- Enter a number in mm/min: millimetres per minute. The form accepts 0.000001 mm/min to 100000 mm/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5000 mm/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from the machine or control specification for threading, which is often below the rapid rate.
What this means: Largest infeed per pass
- What it is
- The largest radial infeed the insert can take in one pass, compared with the first-pass infeed.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.35 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from the insert maker for the insert and pitch.
What this means: Smallest infeed per pass
- What it is
- The smallest radial infeed that still cuts cleanly rather than rubbing, compared with the last-pass infeed.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 1 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.05 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from the insert maker; too many passes can push the last infeed below it.
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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