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Scott Russell straight-line linkage (half-scissor)

How does the Scott Russell linkage make a straight line? · Hardware · basis: Xem Studio design following Brown No. 339 (1868)

Also called: scott russell linkage, scott russell mechanism, exact straight line linkage, mecanismo de Scott Russell, Scott-Russell-Geradführung

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

sizes
4 in table

Notes

  • A bar AB of length 2r has its midpoint C pinned to a radius link OC = r; end A slides on a straight guide through O. Because A, B and O always lie on a circle round C, B moves on the exact straight line through O at right angles to the guide.
  • Here r = 40: bar 80 mm (centre-hole link), radius link 40 mm, A in a 6.2 mm slot; at 35° B is 45.89 mm up the perpendicular. A moves 80·cos φ, B 80·sin φ.
  • Brown's No. 339 (bar on the rod, one end sliding in a fixed slot, radius bar to its middle).
  • Parts (each has its own page): centre-hole-link-80, four-bar-links, slot-guide-plate-90, slide-block-12x6, dowel-pins-metric.
  • Brown's movement No. 339 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Scott Russell straight-line linkage size chart

parametervalue
bar AB80 mm
radius OC40 mm
guide6.2 mm slot
path of Bexact straight line

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. 339: 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

scott-russell-straight-line-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=scott-russell-straight-line-mechanism

Scott Russell straight-line linkage (half-scissor), isometric render of a generated part
Render of scott-russell-straight-line-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
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
Slot guide plate 90 × 30 × 5, 6.2 mm slot (74 long), isometric render of a generated part
Slot guide plate 90 × 30 × 5, 6.2 mm slot (74 long)90.0×30.0×5.0 mm★ 1 file
Slide block 12 × 6.2 mm for a 6.4 mm slot, isometric render of a generated part
Slide block 12 × 6.2 mm for a 6.4 mm slot2 sizes★ 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 does the Scott Russell linkage make a straight line?

A bar AB of length 2r has its midpoint C pinned to a radius link OC = r; end A slides on a straight guide through O. Because A, B and O always lie on a circle round C, B moves on the exact straight line through O at right angles to the guide.