BIZOMAT MAKEOS · Threads
Simple Indexing on a Dividing Head
How many crank turns and holes give this number of divisions on a dividing head?
Crank movement for simple indexing (whole turns plus holes in a circle) for a 40:1 or other worm ratio, using Brown & Sharpe or Cincinnati standard plate hole circles.
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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 (e.g. gear teeth). |
| Worm ratio (crank turns per spindle turn) | :1 | Turns of the crank for one turn of the spindle; 40 on most dividing heads. |
| Index plates available | choice | The index plates fitted to your 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 in one turn of the spindle, for example the number of gear teeth or slots to cut.
- Units and format
- Enter a number in divisions: divisions. The form accepts 2 divisions to 10000 divisions. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 27 divisions as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter the count of divisions, not the angle between them.
What this means: Worm ratio (crank turns per spindle turn)
- What it is
- The number of index crank turns that rotate the dividing head spindle once, set by the head’s worm and wheel.
- Units and format
- Enter a number in :1: a ratio to one (type 3 for 3:1). The form accepts 1 :1 to 1000 :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.
- Effect on the result
- Crank turns per division rise in proportion.
- Get it right
- Read it from the head’s plate or manual; do not assume the common value.
What this means: Index plates available
- What it is
- The set of index plates fitted to your dividing head, which sets the hole circles available for fractional turns.
- Units and format
- Choose one of 2 options from the list: Brown & Sharpe plates 1–3; Cincinnati standard plate (both sides).
- Example
- The form opens with “Brown & Sharpe plates 1–3” selected as a worked example. Choose the option that matches your case.
- Get it right
- Choose the plates you actually have; the tool searches only their hole circles.
Method and formulas
- Crank turns per division = ratio ÷ divisions = whole turns + remainder ÷ divisions.
- A circle with h holes works when remainder × h ÷ divisions is a whole number of holes.
- Brown & Sharpe circles: 15, 16, 17, 18, 19, 20, 21, 23, 27, 29, 31, 33, 37, 39, 41, 43, 47, 49. Cincinnati: 24, 25, 28, 30, 34, 37, 38, 39, 41, 42, 43, 46, 47, 49, 51, 53, 54, 57, 58, 59, 62, 66.
- Example: 27 divisions on a 40:1 head need 1 turns and 13 holes in the 27-hole circle.
Limitations
- Simple indexing only; numbers it cannot produce need differential, compound or angular indexing.
- Hole counts assume standard plates; check the plates on your head.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Index gear teeth, splines and bolt holes on a dividing head
- Check whether simple indexing can produce a number
- Choose the index plate and sector arm setting
Who it is for
- Machinists
- Toolmakers
What you get
- Crank turns per division
- Hole circles that give exact indexing
- Holes to move in each circle
Interpreting the result
- Set the sector arms to span the holes to move plus the one the pin is in.
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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