{
 "version": "2026-10-20",
 "license": "Dimension sheets: CC BY 4.0. Standard and published-size files: CC BY 4.0. Xem Studio's own designs (files_license = Xem Studio Design License): free to use and sell things from, not to redistribute as files — https://xemstudio.com/license/. Other publishers' files: their own license, linked beside them.",
 "slug": "variable-crank-mechanism",
 "name": "Variable crank: a spiral-slotted plate moves the pin along a radial slot",
 "kind": "hardware",
 "category": "Mechanisms",
 "group": "Linkages",
 "year": null,
 "question": "How can the throw of a crank be changed while it runs?",
 "tags": [
  "mechanism",
  "linkages",
  "kinematics",
  "507 mechanical movements"
 ],
 "aliases": [
  "variable crank",
  "adjustable stroke crank",
  "spiral crank",
  "manivela variable",
  "verstellbare Kurbel"
 ],
 "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/variable-crank-mechanism/",
 "sheet_txt": "https://xemstudio.com/objects/variable-crank-mechanism/sheet.txt",
 "sheet": {
  "basis": "Xem Studio design following Brown No. 94 (1868)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Two plates on the crank shaft: one with a radial slot, one with a spiral slot. The crank pin passes through both. Turning one plate against the other moves the pin in or out along the radial slot, changing the crank radius (and the stroke) without stopping.",
   "Here Ø80 plates, slots 6 mm, spiral rising 26 mm per turn (R8 → R34): 0.072 mm of radius per degree. Drawn with the pin at 20 mm (40 mm stroke), the spiral plate turned 166.15°.",
   "Brown's No. 94 (variable crank).",
   "Parts (each has its own page): variable-crank-disc-radial-slot-80, variable-crank-disc-spiral-slot-80, dowel-pins-metric, linear-shafts-h6.",
   "Brown's movement No. 94 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "plates",
     "2 × Ø80 × 6"
    ],
    [
     "pin radius",
     "8 – 34 mm (drawn 20)"
    ],
    [
     "adjustment",
     "26 mm per turn of the spiral"
    ]
   ]
  }
 },
 "sheet_text": "Variable crank: a spiral-slotted plate moves the pin along a radial slot — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/variable-crank-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)\nBasis: Xem Studio design following Brown No. 94 (1868)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Two plates on the crank shaft: one with a radial slot, one with a spiral slot. The crank pin passes through both. Turning one plate against the other moves the pin in or out along the radial slot, changing the crank radius (and the stroke) without stopping.\n- Here Ø80 plates, slots 6 mm, spiral rising 26 mm per turn (R8 → R34): 0.072 mm of radius per degree. Drawn with the pin at 20 mm (40 mm stroke), the spiral plate turned 166.15°.\n- Brown's No. 94 (variable crank).\n- Parts (each has its own page): variable-crank-disc-radial-slot-80, variable-crank-disc-spiral-slot-80, dowel-pins-metric, linear-shafts-h6.\n- Brown's movement No. 94 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.\n\nparameter  value\nplates  2 × Ø80 × 6\npin radius  8 – 34 mm (drawn 20)\nadjustment  26 mm per turn of the spiral\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. 94: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_094.html\n\nFree files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/variable-crank-mechanism/index.json\nAPI: https://xemstudio.com/api/geometry?object=variable-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. 94: figure, his text and an animation",
   "url": "https://507movements.com/mm_094.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": [
  "variable-crank-disc-radial-slot-80",
  "variable-crank-disc-spiral-slot-80",
  "dowel-pins-metric",
  "linear-shafts-h6"
 ],
 "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 can the throw of a crank be changed while it runs?",
   "a": "Two plates on the crank shaft: one with a radial slot, one with a spiral slot. The crank pin passes through both. Turning one plate against the other moves the pin in or out along the radial slot, changing the crank radius (and the stroke) without stopping."
  }
 ],
 "files_license": {
  "name": "Xem Studio Design License",
  "holder": "Xem Studio",
  "url": "https://xemstudio.com/license/",
  "note": "Xem Studio's own design: free to use, print, modify and sell things made from it; not to be republished or redistributed as files."
 },
 "offers": [
  {
   "file": "variable-crank-mechanism-assembly",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "Xem Studio Design License",
   "step": "https://xemstudio.com/files/hardware/variable-crank-mechanism/variable-crank-mechanism-assembly.step",
   "stl": "https://xemstudio.com/files/hardware/variable-crank-mechanism/variable-crank-mechanism-assembly.stl",
   "note": "Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/variable-crank-mechanism/index.md"
}