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Lazy tongs (three-cell scissor linkage)

How much do lazy tongs multiply motion? · Hardware · basis: Xem Studio design following Brown No. 144 (1868)

Also called: lazy tongs, scissor linkage, scissor mechanism, extending tongs, tenazas extensibles (mecanismo de tijera), Nürnberger Schere

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

sizes
4 in table

Notes

  • Crossed bars pinned at their middles and ends: closing the handles a little extends the far end a lot. With n cells the end moves n times as far as the first cell's joint (3 here), and every joint stays on the centre line.
  • Each bar is the 80 mm centre-hole link; length along the axis = 2·n·40·cos α (207.8 mm at α = 30° here).
  • Brown's No. 144 (lazy tongs); the scissor lift and the extending mirror arm are the same linkage.
  • Parts (each has its own page): centre-hole-link-80, dowel-pins-metric.
  • Brown's movement No. 144 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Lazy tongs size chart

parametervalue
cells3
bars6 × 80 mm centre-hole links
angle drawn30° to the axis
reach at 30°207.8 mm

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. 144: figure, his text and an animationwebPublisher's page; dimensions are facts

Free files

★ Free files 1 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json

lazy-tongs-mechanism-assemblyAssembled mechanism, all parts placed at one pose (STEP keeps each part separate)STEP · STL
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Plain text: sheet.txt · JSON: /api/geometry?object=lazy-tongs-mechanism

Lazy tongs (three-cell scissor linkage), isometric render of a generated part
Render of lazy-tongs-mechanism-assembly from the free STEP; not to scale.

Fits with

Centre-hole link, 80 mm (three Ø3 holes: −40, 0, +40), isometric render of a generated part
Centre-hole link, 80 mm (three Ø3 holes: −40, 0, +40)90.0×10.0×5.0 mm★ 1 file
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

How much do lazy tongs multiply motion?

Crossed bars pinned at their middles and ends: closing the handles a little extends the far end a lot. With n cells the end moves n times as far as the first cell's joint (3 here), and every joint stays on the centre line.