Crank and slotted lever quick-return mechanism — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/crank-slotted-lever-quick-return/  (CC BY 4.0)
Basis: Xem Studio drawing; classic mechanism (Brown No. 100)
Catalog version: 2026-10-20

Sizes: see table below
- 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).

parameter  value
crank radius r  25 mm
pivot distance d  50 mm
time ratio  2 : 1
lever  140 mm slotted

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Henry T. Brown (1868, public domain): Five Hundred and Seven Mechanical Movements — scan on archive.org — web — Publisher's page; dimensions are facts — https://archive.org/details/fivehundredseven00browiala

Free files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/crank-slotted-lever-quick-return/index.json
API: https://xemstudio.com/api/geometry?object=crank-slotted-lever-quick-return