KEVOS® MAKEOS · Manufacturing
Multi-Start Thread Turning Set-up
What lead, start spacing and Z shift do I program to turn this multi-start thread?
CNC set-up for multi-start threads: lead (programmed feed) from pitch and starts, the angular spacing of the starts, the Z-axis shift between starts and number of shifts, the helix angle at the pitch diameter for tool side clearance, and the spindle speed limit from the axis feed limit.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Pitch | mm | Pitch (axial distance between adjacent threads). |
| Number of starts | Number of independent thread starts. | |
| Pitch diameter | mm | Pitch diameter of the thread. |
| Maximum Z-axis feed rate | mm/min | Highest feed rate the Z-axis can follow while threading. |
| Planned spindle speed | rpm | Spindle speed you plan to use. |
Method and formulas
- Lead = number of starts × pitch (the F value for G32 or G76).
- Start spacing = 360° ÷ starts; each start is cut after shifting Z by one pitch, with starts − 1 shifts.
- Helix angle = atan[lead ÷ (π × pitch diameter)]; maximum speed = axis feed limit ÷ lead.
- Example: a 3-start thread of 1.5875 mm pitch has a 4.7625 mm lead and a 3.4701° helix angle.
Limitations
- Start the Z shift from the same synchronised position; acceleration distance must clear the part.
- Controls differ in G76 syntax; check the control manual.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Program a two- or three-start thread on a CNC lathe
- Check tool side clearance for a steep lead
- Find the spindle speed the Z-axis can follow
Who it is for
- CNC programmers
- Machinists
- Manufacturing engineers
What you get
- Lead and programmed feed
- Start spacing and Z shift
- Helix angle and speed limit
Interpreting the result
- Steep multi-start leads need extra side clearance on the leading flank of the tool.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1304–1305. Topic reference; no source tables or recommended settings are reproduced.
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