Dividing-Head Simple Indexing
Simple (plain) indexing on a 40:1 (or custom) dividing head.
Example
You enter
- Divisions wanted N 9
- Worm ratio (turns per rev) 40
- Index-plate hole circles (comma list) 27,54
You get
- Turns 4.44444
- Plate settings 4
- Fraction 0.444444
Checked against published worked examples from: U.S. Navy, Naval Education and Training Command.
Details, formula, and sources
ScopeCrank turns per division = ratio / N, plus the exact full-turns-plus-holes setting for each supplied index-plate hole circle that divides evenly (first-principles ratio arithmetic).
Formula or tableTurns per division = ratio / N (40/N on a standard 40:1 head); angular indexing turns = angle x ratio / 360 (angle/9 degrees on 40:1). For a hole circle of H holes the move is the fractional part x H holes, reported when that product is a whole number.
Source and editionSimple (plain) indexing on a 40:1 dividing head - first-principles ratio arithmetic as in Machinery's Handbook (Industrial Press), by name; public domain.
Free accessPure arithmetic, public; differential indexing is out of scope, and angular indexing is the Index-by select (added 2026-10-09).
What governsEstimate. AHJ and licensed professional govern.
API field namesdivisions, worm_ratio, circles, turns, full_turns, fraction
- Worm ratio and plate circles the worm ratio (default 40:1) and the available index-plate hole circles are user-suppliedindexing geometry