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Crank and slotted lever quick-return mechanism

How does a quick-return mechanism work? · Hardware · basis: Xem Studio drawing; classic mechanism (Brown No. 100)

Also called: quick return mechanism, crank and slotted lever, whitworth quick return, shaper mechanism, mecanismo de retorno rápido, Kurbelschleife Schnellrücklauf, mécanisme à retour rapide

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

sizes
4 in table

Notes

  • A crank of radius r turns about a centre a distance d from the lever pivot; its pin, in a slide block, drives a slotted lever. The lever reaches its ends when the crank is square to it, at crank angles ±acos(r/d).
  • Return stroke takes 2·acos(r/d) of crank rotation, the working stroke the rest: time ratio = (360° − 2·acos(r/d)) / (2·acos(r/d)) = 2 : 1 for r = 25, d = 50 mm.
  • Shaping machines use it: slow cut, fast return. Whitworth's version puts the crank pivot inside the lever's path so the lever turns fully round.
  • Parts (each has its own page): crank-discs-5mm-bore, slotted-lever-140, slide-block-12x6, pins-3mm. Brown's movement No. 100 shows it (1868).

Crank and slotted lever quick-return mechanism size chart

parametervalue
crank radius r25 mm
pivot distance d50 mm
time ratio2 : 1
lever140 mm slotted

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

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

Crank and slotted lever quick-return mechanism, isometric render of a generated part
Render of crank-slotted-lever-quick-return-assembly from the free STEP; not to scale.

Fits with

Crank discs for a Ø5 shaft, 10 to 30 mm stroke, isometric render of a generated part
Crank discs for a Ø5 shaft, 10 to 30 mm stroke5 sizes★ 5 files
Slotted lever (quick-return lever), 140 mm, isometric render of a generated part
Slotted lever (quick-return lever), 140 mm3 sizes★ 1 file
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
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

How does a quick-return mechanism work?

A crank of radius r turns about a centre a distance d from the lever pivot; its pin, in a slide block, drives a slotted lever. The lever reaches its ends when the crank is square to it, at crank angles ±acos(r/d).