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Lifting tongs: load-tightened scissor grip

Why do lifting tongs grip harder with a heavier load? · Hardware · basis: Xem Studio design following Brown No. 494 (1868)

Also called: lifting tongs, stone tongs, scissor tongs, self-tightening grab, tenazas de elevación, Hebezange

Exact dimensions. True size, with no printing tolerance added.

sizes
4 in table

Notes

  • Two arms crossed on a pivot, their upper ends drawn together by two equal links meeting at a shackle: the hoist pulls the shackle up, the links pull the arm tops inwards, and the feet below the pivot close on the load. The grip is proportional to the pull, so the heavier the load the tighter it is held.
  • Drawn gripping a 40 mm block: arms crossed at ±22.02°, link holes 60 mm above and feet 80 mm below the pivot, 40 mm links to the shackle pin 88.69 mm above the pivot.
  • Brown's No. 494 (lifting tongs with a shackle and links); ice tongs, log tongs and crane grabs.
  • Parts (each has its own page): lifting-tong-arm-140-foot, tongs-shackle-link-50, load-block-40, four-bar-links, dowel-pins-metric.
  • Brown's movement No. 494 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Lifting tongs: load-tightened scissor grip size chart

parametervalue
arms2, crossed, 60 / 80 mm
links2 × 40 mm
load drawn40 mm block
arm angle±22.02°

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

Henry T. Brown (1868, public domain)Five Hundred and Seven Mechanical Movements — scan on archive.orgwebPublisher's page; dimensions are facts
507movements.comBrown's movement No. 494: figure, his text and an animationwebPublisher's page; dimensions are facts

Free files

★ Free files 1 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json

lifting-tongs-mechanism-assemblyAssembled mechanism, all parts placed at one pose (STEP keeps each part separate)STEP · STL
Let your AI pull this. Add https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.
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Plain text: sheet.txt · JSON: /api/geometry?object=lifting-tongs-mechanism

Lifting tongs: load-tightened scissor grip, isometric render of a generated part
Render of lifting-tongs-mechanism-assembly from the free STEP; not to scale.

Fits with

Lifting tong arm 12 × 5: link hole 60 mm and foot 80 mm either side of the pivot, isometric render of a generated part
Lifting tong arm 12 × 5: link hole 60 mm and foot 80 mm either side of the pivot153.81×19.33×5.0 mm★ 1 file
Tongs shackle link 50 mm centres, 12 × 5, isometric render of a generated part
Tongs shackle link 50 mm centres, 12 × 562.0×12.0×5.0 mm★ 1 file
Block 40 × 40 × 40 (the gripped load), isometric render of a generated part
Block 40 × 40 × 40 (the gripped load)40.0×40.0×40.0 mm★ 1 file
Four-bar links: flat links with 20 to 100 mm hole centres, isometric render of a generated part
Four-bar links: flat links with 20 to 100 mm hole centres7 sizes★ 7 files
Dowel pins, 2–6 mm (ISO 2338 / DIN 6325), isometric render of a generated part
Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)5 sizes★ 23 files

Questions

Why do lifting tongs grip harder with a heavier load?

Two arms crossed on a pivot, their upper ends drawn together by two equal links meeting at a shackle: the hoist pulls the shackle up, the links pull the arm tops inwards, and the feet below the pivot close on the load. The grip is proportional to the pull, so the heavier the load the tighter it is held.