A two-pawl rack lift raises a toothed bar in steps. The lifting pawl advances the rack, while a separate holding pawl supports it during the return stroke. Calculate ideal travel and elapsed time from rack pitch, completed strokes and stroke cadence.
Pawl-Lift Indexing Explorer
Enter rack pitch, a declared number of complete raising strokes and a declared stroke cadence. The worksheet reports ideal indexed travel and elapsed time.
Equation Used
- The rack has uniform pitch p.
- Each complete ideal raising stroke advances exactly one tooth pitch.
- The lifting pawl and holding pawl remain constant-length rigid links in the schematic.
- The holding pawl retains the rack while the lifting pawl returns to the next tooth.
- Load, hand force, efficiency, tooth profile, clearance, spring force, impact, wear, strength and safety are excluded.
The calculation assumes one tooth pitch of travel per completed raising stroke. The drawing uses fixed proportions and slowed playback; entered pitch and cadence determine the numerical travel and time results.
Separate lifting and holding pawls
US Patent 1,918,934 describes a ratchet lifting jack with two pawls. The lifting pawl is operated by a handle and advances the rack bar; the holding pawl prevents descent while the lifting pawl returns to a new engagement position.
During raising, both pawls remain in contact with the rack. The rack teeth pass the holding pawl during upward motion, and the holding pawl supports the rack during the return stroke.
Step-by-step rack lifting
The source establishes a lifting-jack topology: a toothed lifting element, lever-operated lifting pawl and separate holding pawl. This page explains that historical mechanism class only.
It does not assign a capacity or transfer the geometry to bottle jacks, stage machinery, hoists or other devices.
Exact ideal pitch accounting
Under the declared idealization of one pitch per complete raising stroke, s strokes on pitch p give p times s travel. At c strokes per minute, elapsed time is 60s/c.
Declared indexing example
Twelve complete strokes on a 10 mm-pitch rack give 120 mm, or 0.120 m, of ideal indexed travel. At 20 strokes per minute, those strokes take 36 seconds.
Indexing arithmetic is not a jack design
Real load capacity and engagement depend on tooth and pawl geometry, material, section dimensions, pivot placement, contact normals, springs, clearances, impact, wear and the complete load path.
Pitch and stroke count determine travel under the stated assumption. Assessing a real jack also requires its complete geometry, material data and measured engagement behavior; the arithmetic provides no load rating.
Pawl-lift questions
What advances the rack?
The lever-operated lifting pawl.
What prevents descent during return?
The separate holding pawl.
Does one stroke always equal one pitch?
Only in the explicit ideal model used for the arithmetic.
Can this size or certify a jack?
No.
Pawl-lift references
- US Patent 1,918,934, Lifting jack: two-pawl ratchet lifting jack, lever-operated lifting pawl, holding pawl and raising sequence.
- US Patent 1,459,194, Pawl and ratchet jack: spring-pressed lifting and check pawls engaging a vertical rack bar.
- US Patent 1,528,236, Lifting jack: casing, sliding rack, operating lever, lifting pawl and retaining pawl.
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