{
 "version": "2026-10-20",
 "license": "Dimension sheets are written by Xem Studio from the cited sources and are free to use (CC BY 4.0, attribute 'Xem Studio'). Linked files belong to their publishers under the license shown; Xem Studio does not host them. 'license_verified: false' means the license shown is from memory or the publisher's page as last read and should be confirmed at the link before commercial use.",
 "slug": "offset-slotted-crank-mechanism",
 "name": "Offset cranks with slotted arm (variable-speed coupling, Whitworth principle)",
 "kind": "hardware",
 "category": "Mechanisms",
 "group": "Linkages",
 "year": null,
 "question": "How do two offset cranks give a varying speed?",
 "tags": [
  "mechanism",
  "linkages",
  "kinematics",
  "507 mechanical movements"
 ],
 "aliases": [
  "whitworth quick return",
  "offset crank coupling",
  "slotted crank",
  "manivelas descentradas con brazo ranurado",
  "Versetzte Kurbeln mit Schlitzarm"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": false,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/offset-slotted-crank-mechanism/",
 "sheet_txt": "https://xemstudio.com/objects/offset-slotted-crank-mechanism/sheet.txt",
 "sheet": {
  "basis": "Xem Studio design following Brown No. 220 (1868)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Two parallel shafts 5 mm apart: a crank pin on the first slides in a slot on the second. The driven arm runs fast when the pin is nearest its shaft and slow when farthest: speed ratio swings between r/(r − e) and r/(r + e) = 1.71 and 0.71 here.",
   "Whitworth's quick return uses exactly this pair (the driven crank then works a slider), with the pin radius larger than the offset so both turn fully round.",
   "Brown's No. 220.",
   "Parts (each has its own page): crank-disc-36-pin-r12, slotted-crank-arm-30, dowel-pins-metric.",
   "Brown's movement No. 220 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "shaft offset e",
     "5 mm"
    ],
    [
     "pin radius r",
     "12 mm"
    ],
    [
     "speed range",
     "0.71 – 1.71 × input"
    ]
   ]
  }
 },
 "sheet_text": "Offset cranks with slotted arm (variable-speed coupling, Whitworth principle) — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/offset-slotted-crank-mechanism/  (CC BY 4.0)\nBasis: Xem Studio design following Brown No. 220 (1868)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Two parallel shafts 5 mm apart: a crank pin on the first slides in a slot on the second. The driven arm runs fast when the pin is nearest its shaft and slow when farthest: speed ratio swings between r/(r − e) and r/(r + e) = 1.71 and 0.71 here.\n- Whitworth's quick return uses exactly this pair (the driven crank then works a slider), with the pin radius larger than the offset so both turn fully round.\n- Brown's No. 220.\n- Parts (each has its own page): crank-disc-36-pin-r12, slotted-crank-arm-30, dowel-pins-metric.\n- Brown's movement No. 220 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.\n\nparameter  value\nshaft offset e  5 mm\npin radius r  12 mm\nspeed range  0.71 – 1.71 × input\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- 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\n- 507movements.com: Brown's movement No. 220: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_220.html\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/offset-slotted-crank-mechanism/index.json\nAPI: https://xemstudio.com/api/geometry?object=offset-slotted-crank-mechanism\n",
 "sources": [
  {
   "publisher": "Henry T. Brown (1868, public domain)",
   "title": "Five Hundred and Seven Mechanical Movements — scan on archive.org",
   "url": "https://archive.org/details/fivehundredseven00browiala",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "507movements.com",
   "title": "Brown's movement No. 220: figure, his text and an animation",
   "url": "https://507movements.com/mm_220.html",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "crank-disc-36-pin-r12",
  "slotted-crank-arm-30",
  "dowel-pins-metric"
 ],
 "fits": [],
 "dimensions": "exact (nominal, no printing tolerance)",
 "dimension_rule": "All geometry on Xem Studio is exact (nominal, true size) with no printing tolerance. Where a part meets another part, the object lists its mating features (feature, exact size, what it mates with, fit class: press, slide, run, socket, clamp or designed). Apply your process's allowance to those features only; 'designed' gaps are part of the design and stay as drawn.",
 "mating": [],
 "faq": [
  {
   "q": "How do two offset cranks give a varying speed?",
   "a": "Two parallel shafts 5 mm apart: a crank pin on the first slides in a slot on the second. The driven arm runs fast when the pin is nearest its shaft and slow when farthest: speed ratio swings between r/(r − e) and r/(r + e) = 1.71 and 0.71 here."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "offset-slotted-crank-mechanism-assembly",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/offset-slotted-crank-mechanism/offset-slotted-crank-mechanism-assembly.step",
   "stl": "https://xemstudio.com/files/hardware/offset-slotted-crank-mechanism/offset-slotted-crank-mechanism-assembly.stl",
   "note": "Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/offset-slotted-crank-mechanism/index.md"
}