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Scotch yoke: crank pin in a slotted crosshead on pillar guides

What motion does a Scotch yoke give? · Hardware · basis: Xem Studio design following Brown No. 331 (1868)

Also called: scotch yoke, slotted link mechanism, crank and slotted crosshead, simple harmonic motion mechanism, yugo escocés, Kreuzschleife (Schottisches Joch)

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

sizes
4 in table

Notes

  • A crank pin slides in a slot across a crosshead that can only move along two guide pillars: the crosshead position is exactly y = r·sin θ — pure simple harmonic motion, stroke 2r = 24 mm, with no connecting rod.
  • Drawn at θ = 40° with the catalog Ø36 crank disc (pin at 12 mm), a Ø3 pin in the 3 mm slot (contact on both faces) and two Ø5 × 100 linear shafts as the guides.
  • Brown's No. 331 (crank wrist in a slotted cross-head between pillar guides, as in Nos. 93 and 279).
  • Parts (each has its own page): crank-disc-36-pin-r12, scotch-yoke-crosshead-48x14-b5, linear-shafts-h6, dowel-pins-metric.
  • Brown's movement No. 331 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Scotch yoke: crank pin in a slotted crosshead on pillar guides size chart

parametervalue
crank radius r12 mm
stroke24 mm
motiony = r sin θ (simple harmonic)
guides2 × Ø5 shafts, 36 mm apart

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. 331: 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-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-mechanism

Scotch yoke: crank pin in a slotted crosshead on pillar guides, isometric render of a generated part
Render of scotch-yoke-mechanism-assembly from the free STEP; not to scale.

Fits with

Crank disc Ø36 × 5, Ø5 bore, Ø3 pin hole at 12 mm, isometric render of a generated part
Crank disc Ø36 × 5, Ø5 bore, Ø3 pin hole at 12 mm36.0×36.0×5.0 mm★ 1 file
Scotch-yoke crosshead 48 × 14 × 8, 3 mm slot, two Ø5 guide bores, isometric render of a generated part
Scotch-yoke crosshead 48 × 14 × 8, 3 mm slot, two Ø5 guide bores48.0×14.0×8.0 mm★ 1 file
Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long, isometric render of a generated part
Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long10 sizes★ 70 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

What motion does a Scotch yoke give?

A crank pin slides in a slot across a crosshead that can only move along two guide pillars: the crosshead position is exactly y = r·sin θ — pure simple harmonic motion, stroke 2r = 24 mm, with no connecting rod.

How is a Scotch yoke different from a slider-crank?

There is no connecting rod: the pin drives the slot directly, so the motion is an exact sine, not the rod-ratio-distorted motion of a slider-crank.