Xem Studiomeasured geometry

Library › Mechanisms › Linkages ·

Crank pin in a slotted yoke (Scotch yoke)

How does a Scotch yoke turn rotation into pure harmonic motion? · Hardware · basis: Xem Studio design following Brown No. 93 (1868)

Also called: scotch yoke, slotted yoke, harmonic crank, yugo escocés, Kurbelschleife (Scotch Yoke)

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

sizes
4 in table

Notes

  • The crank pin runs in a slot across a sliding yoke, so the yoke moves exactly r·cos θ: simple harmonic motion with no connecting rod and no rod angularity — Brown's 'crank wrist in a slotted yoke'.
  • Catalog Scotch-yoke parts, 30 mm stroke: crank pin at 15 mm carrying a 623 bearing in the 10 mm slot; drawn at 50°, the yoke 9.64 mm from centre. A guide block holds the rod straight.
  • Brown's No. 93.
  • Parts (each has its own page): scotch-yoke, ball-bearings-metric, scotch-yoke-rod-guide-8x8, dowel-pins-metric.
  • Brown's movement No. 93 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Crank pin in a slotted yoke size chart

parametervalue
stroke30 mm
crank radius15 mm
slot10 mm (623 bearing)
motionx = 15 cos θ

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. 93: 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

scotch-yoke-crank-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.
Set it up →

Plain text: sheet.txt · JSON: /api/geometry?object=scotch-yoke-crank-mechanism

Crank pin in a slotted yoke (Scotch yoke), isometric render of a generated part
Render of scotch-yoke-crank-mechanism-assembly from the free STEP; not to scale.

Fits with

Scotch yoke: slotted yoke and crank disc, 20 and 30 mm stroke, isometric render of a generated part
Scotch yoke: slotted yoke and crank disc, 20 and 30 mm stroke2 sizes★ 4 files
Ball bearings, 683 to 6210 and flanged F6xx (ISO 15), isometric render of a generated part
Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)44 sizes★ 44 files
Rod guide 20 × 20 × 18 with an 8 × 8 slot, isometric render of a generated part
Rod guide 20 × 20 × 18 with an 8 × 8 slot20.0×20.0×18.0 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 does a Scotch yoke turn rotation into pure harmonic motion?

The crank pin runs in a slot across a sliding yoke, so the yoke moves exactly r·cos θ: simple harmonic motion with no connecting rod and no rod angularity — Brown's 'crank wrist in a slotted yoke'.