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Watt's linkage (straight-line motion), 60 / 30 / 60

How straight is Watt's linkage? · Hardware · basis: Xem Studio design following Brown No. 337 (1868)

Also called: watts linkage, watt parallel motion, straight line linkage, watt linkage suspension, mecanismo de Watt, Wattsches Gestänge

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

sizes
4 in table

Notes

  • Two equal radius arms swinging in opposite directions, joined by a short coupler: the coupler's midpoint moves on a figure-eight whose middle part is very nearly straight — Watt's 1784 parallel motion for a beam-driven rod.
  • Here: arms 60 mm, coupler 30 mm, fixed pivots ±60 mm apart horizontally and 30 mm vertically. At 12° the midpoint is at x = 0.01 mm (straight line x = 0); over ±10° of arm swing it stays within about 0.1 mm of the line.
  • Brown's No. 337 (radius rod on the lower end of a short link hung from the beam, rod at its centre); the same linkage locates car axles sideways.
  • Parts (each has its own page): four-bar-links, watt-linkage-coupler-30, dowel-pins-metric.
  • Brown's movement No. 337 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Watt's linkage (straight-line motion), 60 / 30 / 60 size chart

parametervalue
radius arms2 × 60 mm
coupler30 mm
fixed pivots(−60, 15) and (60, −15) mm
tracercoupler midpoint

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. 337: 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

watts-linkage-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=watts-linkage-mechanism

Watt's linkage (straight-line motion), 60 / 30 / 60, isometric render of a generated part
Render of watts-linkage-mechanism-assembly from the free STEP; not to scale.

Fits with

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
Watt linkage coupler, 30 mm, centre tracer hole, isometric render of a generated part
Watt linkage coupler, 30 mm, centre tracer hole40.0×10.0×5.0 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 straight is Watt's linkage?

Two equal radius arms swinging in opposite directions, joined by a short coupler: the coupler's midpoint moves on a figure-eight whose middle part is very nearly straight — Watt's 1784 parallel motion for a beam-driven rod.

Is Watt's linkage exactly straight?

No: the midpoint traces a lemniscate-like curve, nearly straight near the middle; Peaucellier's linkage (1864) is the first exact one.