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Planet-gear crank on a carrier round a fixed sun (variable traverse)

How does a planet-gear crank vary a slider's stroke? · Hardware · basis: Xem Studio design following Brown No. 142 (1868)

Also called: planetary crank, variable stroke crank, epicyclic crank traverse, manivela planetaria de carrera variable, Planetenkurbel mit veränderlichem Hub

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

sizes
5 in table

Notes

  • A 30-tooth sun gear is fixed; a carrier disc turns about it carrying a 30-tooth planet that rolls round the sun, making two turns per carrier turn. A crank pin on the planet (10 mm out) therefore traces a curve whose distance from the centre swings between 20 and 40 mm, and the rod from the pin to the slider gives a traverse that lengthens and shortens from stroke to stroke: Brown's variable-traverse motion for winding and tool feeds.
  • Drawn at carrier angle 50° (planet turned 274°): pin at (20.5, 13.06), slider at x = 119.65 on the catalog slot guide, rod 100 mm.
  • Brown's No. 142; module 1 throughout, centre distance 30 mm, the catalog 30 T crank gear and the catalog 30 T gear (sun) on a Ø10 shaft.
  • Parts (each has its own page): spur-gears-module-1, crank-gear-m1-30t-pin-r10, planet-crank-carrier-disc-52-r30-boss10, four-bar-links, slide-block-12x6, slot-guide-plate-90, linear-shafts-h6, dowel-pins-metric.
  • Brown's movement No. 142 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Planet-gear crank on a carrier round a fixed sun size chart

parametervalue
sun / planet30 T / 30 T, module 1
carrier radius30 mm
crank pin10 mm on the planet
effective crank20 – 40 mm
rod100 mm

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. 142: 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

planetary-crank-variable-traverse-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=planetary-crank-variable-traverse-mechanism

Planet-gear crank on a carrier round a fixed sun (variable traverse), isometric render of a generated part
Render of planetary-crank-variable-traverse-mechanism-assembly from the free STEP; not to scale.

Fits with

Spur gears, module 1: 10 to 80 teeth (20° involute), isometric render of a generated part
Spur gears, module 1: 10 to 80 teeth (20° involute)26 sizes★ 26 files
Crank gear, module 1, 30 T with a Ø3 crank-pin hole at 10 mm, isometric render of a generated part
Crank gear, module 1, 30 T with a Ø3 crank-pin hole at 10 mm31.99×31.89×8.0 mm★ 1 file
Planet carrier disc Ø52 × 5 with a Ø10 × 13 planet boss at 30 mm, isometric render of a generated part
Planet carrier disc Ø52 × 5 with a Ø10 × 13 planet boss at 30 mm61.0×52.0×18.0 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
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
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
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

How does a planet-gear crank vary a slider's stroke?

A 30-tooth sun gear is fixed; a carrier disc turns about it carrying a 30-tooth planet that rolls round the sun, making two turns per carrier turn. A crank pin on the planet (10 mm out) therefore traces a curve whose distance from the centre swings between 20 and 40 mm, and the rod from the pin to the slider gives a traverse that lengthens and shortens from stroke to stroke: Brown's variable-traverse motion for winding and tool feeds.