{
 "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": "eccentric-gear-and-pinion-mechanism",
 "name": "Eccentric spur gear and pinion on a swinging arm (variable speed)",
 "kind": "hardware",
 "category": "Mechanisms",
 "group": "Gears",
 "year": null,
 "question": "How does an eccentric gear give a varying speed?",
 "tags": [
  "mechanism",
  "gears",
  "kinematics",
  "507 mechanical movements"
 ],
 "aliases": [
  "eccentric gear drive",
  "variable speed gear",
  "off centre gear and pinion",
  "engranaje excéntrico y piñón",
  "Exzenterrad mit Ritzel"
 ],
 "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/eccentric-gear-and-pinion-mechanism/",
 "sheet_txt": "https://xemstudio.com/objects/eccentric-gear-and-pinion-mechanism/sheet.txt",
 "sheet": {
  "basis": "Xem Studio design following Brown No. 222 (1868)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A 40-tooth gear turns on a shaft 5 mm off its centre; a 20-tooth pinion on a swinging arm follows it, held at the exact 30 mm centre distance by a link from the gear's centre stud. The pinion's speed varies each turn as its contact point moves nearer and farther from the shaft: between about 0.75 and 1.25 of the mean 2 : 1 ratio.",
   "Drawn at 60° of shaft rotation: gear centre at (2.5, 4.33), pinion at (27.9, 20.29), arm pivot at (50, 0). Module 1, teeth in mesh with no backlash drawn.",
   "Brown's No. 222 (eccentric wheel with a link in place of the groove of No. 221).",
   "Parts (each has its own page): eccentric-spur-gear-m1-40t-e5-b5, spur-gears-module-1, swing-arm-30-holes-3-and-6, dowel-pins-metric.",
   "Brown's movement No. 222 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "gear",
     "40 T, bore 5 mm off centre"
    ],
    [
     "pinion",
     "20 T on a 30 mm arm"
    ],
    [
     "link",
     "30 mm, centre to centre"
    ],
    [
     "speed swing",
     "0.75 – 1.25 × mean"
    ]
   ]
  }
 },
 "sheet_text": "Eccentric spur gear and pinion on a swinging arm (variable speed) — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/eccentric-gear-and-pinion-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)\nBasis: Xem Studio design following Brown No. 222 (1868)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A 40-tooth gear turns on a shaft 5 mm off its centre; a 20-tooth pinion on a swinging arm follows it, held at the exact 30 mm centre distance by a link from the gear's centre stud. The pinion's speed varies each turn as its contact point moves nearer and farther from the shaft: between about 0.75 and 1.25 of the mean 2 : 1 ratio.\n- Drawn at 60° of shaft rotation: gear centre at (2.5, 4.33), pinion at (27.9, 20.29), arm pivot at (50, 0). Module 1, teeth in mesh with no backlash drawn.\n- Brown's No. 222 (eccentric wheel with a link in place of the groove of No. 221).\n- Parts (each has its own page): eccentric-spur-gear-m1-40t-e5-b5, spur-gears-module-1, swing-arm-30-holes-3-and-6, dowel-pins-metric.\n- Brown's movement No. 222 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.\n\nparameter  value\ngear  40 T, bore 5 mm off centre\npinion  20 T on a 30 mm arm\nlink  30 mm, centre to centre\nspeed swing  0.75 – 1.25 × mean\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. 222: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_222.html\n\nFree files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/eccentric-gear-and-pinion-mechanism/index.json\nAPI: https://xemstudio.com/api/geometry?object=eccentric-gear-and-pinion-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. 222: figure, his text and an animation",
   "url": "https://507movements.com/mm_222.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": [
  "eccentric-spur-gear-m1-40t-e5-b5",
  "spur-gears-module-1",
  "swing-arm-30-holes-3-and-6",
  "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 does an eccentric gear give a varying speed?",
   "a": "A 40-tooth gear turns on a shaft 5 mm off its centre; a 20-tooth pinion on a swinging arm follows it, held at the exact 30 mm centre distance by a link from the gear's centre stud. The pinion's speed varies each turn as its contact point moves nearer and farther from the shaft: between about 0.75 and 1.25 of the mean 2 : 1 ratio."
  }
 ],
 "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": "eccentric-gear-and-pinion-mechanism-assembly",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "Xem Studio Design License",
   "step": "https://xemstudio.com/files/hardware/eccentric-gear-and-pinion-mechanism/eccentric-gear-and-pinion-mechanism-assembly.step",
   "stl": "https://xemstudio.com/files/hardware/eccentric-gear-and-pinion-mechanism/eccentric-gear-and-pinion-mechanism-assembly.stl",
   "note": "Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/eccentric-gear-and-pinion-mechanism/index.md"
}