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Constant-breadth cam turning in a yoke (three strokes per turn)

How does a constant-breadth cam reciprocate a bar? · Hardware · basis: Xem Studio design following Brown No. 276 (1868)

Also called: constant breadth cam, reuleaux cam yoke, three throw cam, leva de anchura constante en yugo, Gleichdick im Rahmen

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

sizes
4 in table

Notes

  • A cam of constant breadth (a Reuleaux triangle with rounded corners) turns about its centre between two parallel faces of a yoke exactly its breadth apart, so it touches both at every angle and drives the yoke both ways. Its distance to each face changes from the corner radius to the flank radius: the yoke moves 4.64 mm to and fro three times per turn of the cam.
  • Breadth 40 (side 30, corners R5); drawn at 20°, the yoke 2.06 mm from centre.
  • Brown's No. 276 (cam giving a reciprocating motion to a bar); the corner-pivoted triangle of No. 91 gives one long stroke with dwells instead.
  • Parts (each has its own page): constant-breadth-cam-s30-r5-bore5, constant-breadth-cam-yoke-40, dowel-pins-metric.
  • Brown's movement No. 276 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Constant-breadth cam turning in a yoke size chart

parametervalue
breadth40 mm
pivotcentre
stroke4.64 mm
strokes per turn3

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. 276: 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

constant-breadth-cam-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=constant-breadth-cam-yoke-mechanism

Constant-breadth cam turning in a yoke (three strokes per turn), isometric render of a generated part
Render of constant-breadth-cam-yoke-mechanism-assembly from the free STEP; not to scale.

Fits with

Constant-breadth cam: rounded Reuleaux triangle, breadth 40, Ø5 bore at its centre, isometric render of a generated part
Constant-breadth cam: rounded Reuleaux triangle, breadth 40, Ø5 bore at its centre40.0×40.0×8.0 mm★ 1 file
Yoke 52 × 62.64 with a 40 mm wide opening and two 8 × 8 rods, isometric render of a generated part
Yoke 52 × 62.64 with a 40 mm wide opening and two 8 × 8 rods132.0×62.64×8.0 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 constant-breadth cam reciprocate a bar?

A cam of constant breadth (a Reuleaux triangle with rounded corners) turns about its centre between two parallel faces of a yoke exactly its breadth apart, so it touches both at every angle and drives the yoke both ways. Its distance to each face changes from the corner radius to the flank radius: the yoke moves 4.64 mm to and fro three times per turn of the cam.