A click-driven cog-wheel feed is an intermittent rotary drive where a spring-loaded pawl — the click — rocks back and forth on each stroke and pushes a cog wheel forward by one tooth at a time. Unlike a continuous gear train that spins smoothly, this drive converts a reciprocating input into precise step-wise rotation. It exists to advance work in fixed increments without a clutch, brake or servo. You see it in printing presses, paper feeders and old letterpress typecasting where each pull of a lever moves the sheet exactly one pitch.
Click-driven Cog-wheel Feed Interactive Calculator
Vary tooth count, teeth advanced per stroke, and stroke count to see the indexed rotation of a pawl-and-ratchet feed.
Equation Used
The calculator uses the ratchet indexing relationship: each stroke advances k teeth on a cog with N teeth, so the angular index is 360k/N degrees per stroke. Multiplying by the number of strokes gives the accumulated output angle.
- Pawl seats cleanly and advances an integer number of teeth.
- Holding pawl prevents reverse motion on the return stroke.
- Ratchet teeth are evenly spaced.
- No slip, rebound, or skipped teeth are included.
The animation uses an oscillating disk and pivoted click based on Brown movement 121, with an added holding click for one-direction indexing. Its teeth and pawl springs are illustrative. The calculator counts ideal tooth advances; it does not predict feed force, skipping, speed limits or wear. N/k is an equivalent stroke count; an actual machine completes an integer number of strokes.
How the click-driven feed works
An input rod rocks a disk about the output shaft. The disk carries a pivoted click that engages a cog tooth during the drive stroke. On return, the click rises over the teeth. Brown’s movement 121 illustrates this disk-and-click arrangement and describes reversing it by throwing the click over. The animation shows one selected drive direction and adds a separate holding click so the output remains stationary on return.
Connected parts
- The carrier disk oscillates freely around the output shaft.
- The cog wheel is fixed to the output shaft.
- The driving click pivots on the carrier; its tip meets the drawn tooth profile.
- The illustrated holding click has a frame-mounted pin.
- The input connecting rod has constant length and a guided sliding end.
Successful indexing also depends on backlash, tooth and pawl geometry, spring response and load. Those effects require a detailed design and are outside this tooth-count calculator.
Where an intermittent click feed is useful
Brown identifies feed motions for planing machines and other tools. The broader principle is useful when a reciprocating input must produce discrete rotary increments. A roller or screw on the output shaft can convert those increments into a linear feed, but its dimensions and any intermediate transmission ratio must also be included.
Indexing equations
For N evenly spaced teeth and k teeth advanced each stroke:
Step angle = 360k/N degrees; total angle after s strokes = 360ks/N; index per stroke = 100k/N percent.
The equivalent stroke count for one revolution is N/k. When this is not an integer, no whole stroke ends at exactly one revolution; the wheel completes an exact whole-turn cycle after N/gcd(N,k) strokes.
If an output roller of diameter D turns directly with the cog, the ideal linear feed is πDk/N per stroke. A transmission multiplies that by the roller-to-cog angular speed ratio. Slip is not included.
Worked example: 16-tooth indexing wheel
With N = 16 and k = 1, each drive stroke advances 22.5°, or 6.25% of a revolution. Sixteen strokes complete one revolution. Selecting a batch of five strokes gives 112.5° of total rotation.
For comparison, a 38 mm roller directly attached to a 12-tooth cog advances π × 38/12 = 9.95 mm per tooth, not 60 mm. Achieving 60 mm per stroke would require a different roller diameter or a roller-to-cog speed ratio of about 6.03:1. A speed reduction would decrease the feed further.
Choosing an indexing mechanism
A click feed suits a reciprocating source and fixed tooth increments. A Geneva mechanism accepts continuous rotary input and creates an index-and-dwell sequence. A controlled motor can provide programmable angles. Required load, backlash, indexing accuracy and operating speed determine which approach is suitable; this calculator does not assign universal speed or life ratings.
Questions about click feeds
Why does the cog stop during the return stroke?
The driving click rides over the teeth while the holding click prevents reverse rotation. The calculation assumes successful engagement without rebound or slip.
Can this arrangement reverse?
Brown’s original illustration uses a reversible click. This visualization shows one direction and a holding click; a reversible machine must also release or rearrange its holding device.
Does the stroke count set speed?
No. It sets the number of indexing cycles represented by one displayed batch. The animation runs at an illustrative rate, not a rated machine speed.
What happens if N/k is fractional?
It is an equivalent number of strokes per revolution. For example, 13 teeth with two teeth advanced per stroke gives 6.5 equivalent strokes per revolution, but the wheel needs 13 whole strokes to return to its initial angular orientation after two turns.
References & Further Reading
- Henry T. Brown, Five Hundred and Seven Mechanical Movements, printed pages 34–35, movement 121. Original disk, click and reciprocating-rod arrangement.
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