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Drag-link (double-crank) four-bar

What is a drag-link mechanism? · Hardware · basis: Xem Studio drawing; classic mechanism (Brown No. 231)

Also called: drag link mechanism, double crank mechanism, grashof four bar, mecanismo de doble manivela, mecanismo de dupla manivela, Doppelkurbel, double manivelle

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

sizes
4 in table

Notes

  • A four-bar whose shortest link is the fixed frame: both cranks turn fully round. Grashof: s + l ≤ p + q (20 + 50 ≤ 45 + 40).
  • Input turns at constant speed, output at varying speed — the base of quick-return drives and some shaper and press mechanisms.
  • Built from four-bar links of the lengths in the table.
  • Parts (each has its own page): four-bar-links, pins-3mm. Brown's movement No. 231 shows it (1868).

Drag-link (double-crank) four-bar size chart

parametervalue
frame (shortest) s20 mm
input crank40 mm
coupler50 mm
output crank45 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

Free files

★ Free files 1 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json

drag-link-mechanism-assemblyAssembled mechanism, all parts placed (STEP keeps each part separate)STEP · STL
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Plain text: sheet.txt · JSON: /api/geometry?object=drag-link-mechanism

Drag-link (double-crank) four-bar, isometric render of a generated part
Render of drag-link-mechanism-assembly from the free STEP; not to scale.

Fits with

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
Crank and wrist pins Ø3 × 12, 16, 19, 20 and 23, isometric render of a generated part
Crank and wrist pins Ø3 × 12, 16, 19, 20 and 235 sizes★ 5 files

Questions

What is a drag-link mechanism?

A four-bar whose shortest link is the fixed frame: both cranks turn fully round. Grashof: s + l ≤ p + q (20 + 50 ≤ 45 + 40).