Dividing Head Indexing Calculator

Inputs

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Divide a full circle into N parts, or advance by a given angle.
Equal divisions of a full circle (gear teeth, flutes, holes). Used in divisions mode.
Whole or decimal degrees. Used in angle mode.
°
Arc-minutes (1/60 degree). Used in angle mode.
Arc-seconds (1/3600 degree). Used in angle mode.
Crank turns per spindle revolution: 40:1 standard dividing heads, 90:1 common rotary tables.
: 1
Standard Brown & Sharpe three-plate set, or a single circle you specify (Cincinnati and import sets differ).
Hole count of your plate circle. Used when the index plate is set to custom.

Results

Default result
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Crank turns per index(T)
1.48148
Pass

1 turn + 13 holes on the 27-hole circle.

Exact turns required: whole turns plus a fraction made on the plate.

Also computed

Whole turns1

Hole circle(c)Pass27

Plate circle to pin — smallest exact circle when several work.

Holes to advance(h)13

Hole spaces beyond the starting hole — set the sector arms to this count.

Achieved increment13.3333°

Error per index0

The circle divides exactly.

Arc-seconds; zero when a circle divides exactly.

Method notes 3 notes
  • Turns = R / N; one crank turn moves the spindle 9° at this worm ratio.
  • Holes to advance are hole SPACES beyond the starting hole — set the sector arms to span them and the start hole does not count.
  • Standard B&S plates: 15-16-17-18-19-20 · 21-23-27-29-31-33 · 37-39-41-43-47-49. Cincinnati and import sets differ — enter yours as a custom circle.

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