KEVOS® MAKEOS · Threads
Change Gears for Thread Cutting
Which change gears cut this thread lead on this lathe?
Best simple and compound change-gear trains from a standard gear set to cut a required metric or inch lead with a given leadscrew, with the resulting lead error.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Thread to cut is given as | choice | Whether the thread is metric (pitch) or inch (TPI). |
| Thread to cut | mm or TPI | Pitch in millimetres or threads per inch of the thread to cut. |
| Leadscrew is given as | choice | Leadscrew specification. |
| Leadscrew | mm or TPI | Leadscrew pitch or threads per inch, from the lathe plate or manual. |
| Fixed ratio in the headstock (spindle to stud) | :1 | Any fixed reduction between the spindle and the first change-gear stud (1 if none). |
| Gear set | choice | The change gears available; check your actual set (one of each size assumed). |
Method and formulas
- Required ratio (driver ÷ driven product) = lead to cut ÷ (leadscrew lead × fixed ratio), all leads in mm.
- Simple train A ÷ B; compound train (A ÷ B) × (C ÷ D), each gear used once.
- Error = (train ratio ÷ required − 1) × 100%; 25.4 mm = 127 ÷ 5 × 1 mm makes 127-tooth gears exact for metric–inch conversions.
- Example: 1.5 mm pitch on an 8 TPI leadscrew: drivers 20 and 75, driven 25 and 127 (error 0%).
Limitations
- Gear meshing and clearance on the banjo are not checked; some compound trains may not fit your lathe.
- One of each gear size is assumed.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set up a manual lathe for a non-standard pitch
- Cut metric threads with an inch leadscrew (or the reverse)
- Check the error of an approximate gear train
Who it is for
- Machinists
- Toolmakers
What you get
- Required gear ratio
- Best two-gear train and its error
- Best four-gear compound train and its error
Interpreting the result
- For an approximate train, multiply the error by the thread length to see the accumulated lead error.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2043–2049. Topic reference; no source tables or recommended settings are reproduced.
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