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Constant-diameter cam between two rollers in a yoke

How can a cam drive a yoke both ways without a spring? · Hardware · basis: Xem Studio design following Brown No. 117 (1868)

Also called: constant diameter cam, cam and yoke, positive drive cam, cam between two rollers, leva de diámetro constante entre rodillos, Gleichdickkurve im Rollenrahmen

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

sizes
4 in table

Notes

  • The cam turns between two rollers carried on one yoke. Its pitch curve has a constant diameter (opposite radii always add to the roller spacing), so both rollers stay in contact all round and the yoke is pushed one way by one roller's side of the cam and back by the other's.
  • Pitch curve r = 22 + 6 sin θ − sin 3θ, rollers Ø10 (623 bearings on Ø3 pins) 44 mm apart: stroke 14 mm per turn. Drawn at 35°: yoke -2.48 mm from centre, both rollers touching.
  • Brown's No. 117 (a cam between two rollers in a yoke working a slide-valve rod).
  • Parts (each has its own page): constant-diameter-cam-c22-a6-b1-bore8, two-roller-cam-yoke-44-rods-8, ball-bearings-metric, dowel-pins-metric, linear-shafts-h6.
  • Brown's movement No. 117 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Constant-diameter cam between two rollers in a yoke size chart

parametervalue
pitch curve22 + 6 sin θ − sin 3θ
roller spacing44 mm
stroke14 mm
rollers623 bearings

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. 117: 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

cam-between-rollers-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.
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Plain text: sheet.txt · JSON: /api/geometry?object=cam-between-rollers-yoke-mechanism

Constant-diameter cam between two rollers in a yoke, isometric render of a generated part
Render of cam-between-rollers-yoke-mechanism-assembly from the free STEP; not to scale.

Fits with

Constant-diameter cam for two Ø10 rollers 44 mm apart, 4 thick, Ø8 bore, isometric render of a generated part
Constant-diameter cam for two Ø10 rollers 44 mm apart, 4 thick, Ø8 bore34.42×34.0×4.0 mm★ 1 file
Two-roller cam yoke, roller pins 44 mm apart, 8 × 8 rods, isometric render of a generated part
Two-roller cam yoke, roller pins 44 mm apart, 8 × 8 rods142.0×18.0×5.0 mm★ 1 file
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
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
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

Questions

How can a cam drive a yoke both ways without a spring?

The cam turns between two rollers carried on one yoke. Its pitch curve has a constant diameter (opposite radii always add to the roller spacing), so both rollers stay in contact all round and the yoke is pushed one way by one roller's side of the cam and back by the other's.