Explore how two crossed jaw members open and close through a pair of lifting links. This symmetric model compares pivot span, contact-face gap and eye height; it simplifies the arrangement in US7673917B2 and does not assign a lifting capacity.
Lifting Tongs Interactive Calculator
Vary jaw-member half-length, direct lifting-link length and maximum arm angle to inspect the declared symmetric analogy. Pinned swivelling shoes are shown explicitly, and the actual visible contact-face gap is reported separately from jaw-end pivot span.
Equation Used
- The two idealized jaw members are equal and cross at their midpoint pin.
- The two idealized direct links have equal length B and share a common apex.
- Each shoe swivels about the white jaw-end pin and is displayed horizontal; its schematic physical reach is limited to 8-30 mm by the declared formula.
- The model is planar and symmetric; no load, grip, contact-pressure or capacity inference is made.
The shoes swivel about the jaw-end pins, so the visible contact gap differs from the distance between those pins. The outputs describe these geometric positions, not grip force or load capacity.
Simplified lift-to-close analogy
The cited patent supports opposed jaw members on a central fastener and a lifting-linkage assembly joined at an apex. Its disclosed mechanism also includes lobes, retainer plates, fixed and slotted apertures and multiple fasteners.
The calculator deliberately simplifies that architecture to two equal crossed members and two equal direct links. Each lower shoe is drawn as a separate pinned swivel. This is an idealized teaching geometry, not an exact patent reconstruction or a lifting-device design.
Use as a geometry illustration only
The animation can show how a declared symmetric linkage opens and closes and how jaw-end pivot span differs from visible contact-face gap. It cannot select, rate, inspect or approve lifting tongs.
Real below-the-hook devices require device-specific design, marking, testing, inspection, maintenance and operating instructions.
Declared symmetric coordinates
Jaw-end pivot span is 2x. Each schematic swivelling shoe reaches inward by min(30,max(8,0.18x)) mm, so the visible contact-face gap is 2(x-shoe reach). The jaw-member vertical span is 2v. These are idealized distances only.
Worked geometry example
At any selected phase, the calculator solves the two jaw-end pivots, the two upper pivots and the common eye from A, B and beta. It then subtracts the declared reach of both pinned shoes to report the contact-face gap actually drawn.
No force, friction coefficient, safety factor, working load or proof-test value is inferred.
Model boundary
The simplified analogy omits the patent's lobes, slots, retainers and multiple fasteners, as well as plate thickness, locks, contact mechanics, friction, material strength and stability. It cannot be used for fabrication or rigging decisions.
Lifting-tongs geometry questions
Is this the exact mechanism in US7673917B2?
No. It is a simplified symmetric analogy inspired by the patent's qualitative lift-to-close architecture.
Why are the shoes horizontal while the jaws rotate?
They are separate pinned swivelling members, shown by the white end pins. Their orientation is a declared schematic constraint.
Does contact-face gap predict grip or capacity?
No. It is only the visible distance between the two brown faces.
Mechanism and scope references
- US7673917B2, Variable diameter lifting tongs: describes opposed jaw members pivoting about a central fastener and a two-arm lifting linkage joined at an apex that closes the jaws when lifted.
- ASME B30.20, Below-the-Hook Lifting Devices: places clamps and other below-the-hook devices within operational requirements; it does not validate or rate this geometry calculator.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
