This slotted-rack indexer uses an oscillating lever, a driving pawl and a holding pawl. The calculator assumes one successful slot-pitch advance per completed cycle; the animation shows drive and reset as distinct phases.
Lever to Slotted Rack via Two Hooked Pawls Interactive Calculator
Choose a declared slot pitch and a number of successful indexing strokes. The calculator reports ideal cumulative travel while the visual shows one explanatory drive-and-hold cycle plus a clearly labelled, disengaged diagram replay cut.
Equation Used
- Each counted cycle completes exactly one successful pitch advance.
- The holding pawl prevents reverse motion during the lever reset phase.
- Pawl lift and return timing are prescribed in the drawing and require an external cam, spring or stop constraint that is not modeled.
- Slip, missed indexes, double indexes, deformation, impact and wear are excluded.
Each counted successful index adds one slot pitch to total travel. Pawl timing is prescribed for illustration, and the disengaged replay interval simply restarts the diagram. Engagement reliability requires the actual contact geometry, loads and operating conditions.
Drive, hold and reset
On the working stroke, the lever-carried driving pawl bears on a slot face and advances the rack. A frame-carried holding pawl then retains the indexed position while the lever and driving pawl return for the next cycle.
The animation displays one declared pitch of rack motion during drive and no reverse rack motion during held reset. Its timed pawl lift and return path is prescribed, representing an external cam, spring or stop constraint that is not modeled; it is not presented as a passive single-lever solution.
At the end, both pawls visibly disengage under a Diagram replay label before the one-index example restarts at its zero reference. That replay cut is not physical reverse travel.
Use the result as ideal index arithmetic
The calculation can convert a declared rack pitch and count of successful indexes into cumulative ideal travel. It does not establish that an arbitrary mechanism will index once per stroke.
A physical design needs exact slot and pawl profiles, pivot locations, spring characteristics, clearances, stops, load, speed, impact, friction, materials, strength, wear and a release or reset method where required.
Declared one-pitch indexing
Here p is centre-to-centre slot pitch and N is the number of completed successful one-pitch indexes. The result is an ideal commanded distance. It contains no probability or efficiency factor because engagement reliability is not derivable from the two entered values.
Worked arithmetic example
For a declared 5.0 mm slot pitch and 20 completed successful indexes, ideal cumulative advance is 20×5.0 = 100.0 mm. The ideal per-stroke advance is 5.0 mm and ideal reverse travel during each held reset is zero.
Model boundaries
Index reliability depends on slot contact, spring behavior and the dynamics of the complete mechanism. Hook angle and spring preload cannot be assessed independently of the exact geometry, material, load and speed.
The explanatory drawing does not specify tooth width, hook angle, spring force, clearance, safe load, accuracy or service life.
Two-pawl rack questions
Why are there two pawls?
One advances the rack during the working stroke; the other holds the indexed position while the drive pawl resets.
What actuates the illustrated pawl path?
The animation prescribes pawl lift and return timing as if an external cam, spring or stop constrained it. Those parts are not modeled; a physical mechanism needs an arrangement to control the illustrated pawl motion.
Why does the diagram restart?
The final labelled replay interval lifts both pawls clear, then the explanatory one-index scene cuts back to its zero reference. It is a presentation restart, not reverse rack motion.
Does one stroke always equal one pitch?
Only by the declared ideal assumption. A real design must constrain the stroke and contact geometry so the pawl enters the intended slot without missing or double-indexing.
Can this calculate the probability of a missed index?
No. Slot pitch and stroke count determine ideal travel, but do not describe the contact, spring and dynamic behavior needed to assess indexing reliability.
Does the drawing specify a buildable pawl?
No. It is a phase diagram. Manufacturing geometry needs a detailed contact and strength design.
Historical mechanism references
- US Patent 620,441, Automatic Gate (1899): documents a lever arrangement with a pair of spring-biased pawls acting on a rack.
- US Patent 3,953,119, Slide Projector and Indexing Mechanism (1976): documents an indexing lever carrying pawls through a travel corresponding to adjacent rack teeth.
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