Xem Studiomeasured geometry

Library › Mechanisms › Linkages ·

Parallel cranks and coupling rods, two pairs at 90° (no dead centre)

Why are coupling rods set 90° apart? · Hardware · basis: Xem Studio design following Brown No. 230 (1868)

Also called: coupling rods, parallel crank coupling, quartered cranks, parallelogram linkage, manivelas paralelas con bielas de acoplamiento, Parallelkurbelkupplung (Kuppelstangen)

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

sizes
5 in table

Notes

  • Two shafts 80 mm apart each carry two cranks of equal radius; equal rods join crank to crank, so the shafts turn together at exactly the same speed (a parallelogram linkage). One pair alone would jam or flip at its two dead centres (rod in line with the cranks); a second pair set at 90° is at full leverage exactly then, so the drive never stops — no flywheel needed.
  • Catalog Ø36 crank discs (pin at 12 mm) and 80 mm links: the rod length equals the shaft distance, which makes every rod parallel to the line of shafts.
  • Brown's No. 230 (circular into circular motion by two pairs of connecting rods at right angles); the quartered cranks of locomotive coupling rods.
  • Parts (each has its own page): crank-disc-36-pin-r12, four-bar-links, dowel-pins-metric.
  • Brown's movement No. 230 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Parallel cranks and coupling rods, two pairs at 90° size chart

parametervalue
shaft centres80 mm
crank radius12 mm
rods2 × 80 mm
crank phase90°
ratio1 : 1, same direction

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. 230: 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

parallel-crank-coupling-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=parallel-crank-coupling-mechanism

Parallel cranks and coupling rods, two pairs at 90° (no dead centre), isometric render of a generated part
Render of parallel-crank-coupling-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
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
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

Why are coupling rods set 90° apart?

Two shafts 80 mm apart each carry two cranks of equal radius; equal rods join crank to crank, so the shafts turn together at exactly the same speed (a parallelogram linkage). One pair alone would jam or flip at its two dead centres (rod in line with the cranks); a second pair set at 90° is at full leverage exactly then, so the drive never stops — no flywheel needed.