BIZOMAT MAKEOS · Threads
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.
Open the calculatorRuns in your browser. No account needed.
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. |
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: Number of divisions
- What it is
- The number of equal divisions needed around the work, such as the number of teeth on a gear being cut.
- Units and format
- Enter a number in divisions: divisions. The form accepts 2 divisions to 2000 divisions. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 67 divisions as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- If simple indexing can already produce this number, the tool says so instead of giving differential gears.
What this means: Worm ratio
- What it is
- The worm-and-wheel ratio of the dividing head: the number of crank turns needed for one full turn of the spindle.
- Units and format
- Enter a number in :1: a ratio to one (type 3 for 3:1). The form accepts 1 :1 to 200 :1. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 :1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Check the plate on your dividing head; most use 40, but some use other ratios.
What this means: Change gears available
- What it is
- Which set of change gears you have for the dividing head, which limits the gear trains the tool can propose.
- Units and format
- Choose one of 2 options from the list: Standard dividing head set: 24, 24, 28, 32, 40, 44, 48, 56, 64, 72, 86, 100; 24 to 100 in steps of 4.
- Example
- The form opens with “Standard dividing head set: 24, 24, 28, 32, 40, 44, 48, 56, 64, 72, 86, 100” selected as a worked example. Choose the option that matches your case.
- Get it right
- Choose the set you actually have; a train using a gear you do not own cannot be set up.
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.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Differential Indexing on a Dividing Head calculator