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Differential Indexing on a Dividing Head
How can this number of divisions be indexed when simple indexing cannot do it?
An approximate number, crank movement and change gears for differential indexing on a 40:1 dividing head with the standard gear set, for numbers simple indexing cannot produce.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Number of divisions | divisions | Number of equal divisions required. |
| Worm ratio | :1 | Crank turns per spindle turn (40 on most heads). |
| Change gears available | choice | Change gears supplied with your dividing head. |
Method and formulas
- Choose an approximate number A that simple indexing can produce; index for A. Numbers giving a simple two-gear train are preferred, then the closest A.
- Gear ratio (driver on spindle ÷ driven on worm) = (A − N) × 40 ÷ A (use N − A when A < N).
- A > N: index plate turns the same way as the crank; A < N: the opposite way (set with idlers).
- Example: 67 divisions: index for 70 and gear 48 on the spindle driving 28 on the worm.
Limitations
- Gearing must be fitted with the plate unlocked; check your head’s instructions for idler positions.
- Only exact gear trains from the selected set are offered.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Index prime and awkward numbers of teeth
- Set up the dividing head gearing
- Check a differential indexing table
Who it is for
- Machinists
- Toolmakers
What you get
- Approximate number used
- Crank movement for the approximate number
- Change gears (spindle to worm) and idler arrangement
Interpreting the result
- Check the first few divisions with a test cut before cutting the full part.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2107–2121. Topic reference; no source tables or recommended settings are reproduced.
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