{
 "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": "jockey-pulley-belt-tightener-mechanism",
 "name": "Jockey (tightening) pulley engaging a slack belt",
 "kind": "hardware",
 "category": "Mechanisms",
 "group": "Belt and friction drives",
 "year": null,
 "question": "How does a jockey pulley start and stop a belt drive?",
 "tags": [
  "mechanism",
  "belt and friction drives",
  "kinematics",
  "507 mechanical movements"
 ],
 "aliases": [
  "jockey pulley",
  "belt tightener",
  "idler pulley clutch",
  "tensioner pulley",
  "polea tensora (embrague por tensor)",
  "Spannrolle (Riemenspanner)"
 ],
 "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/jockey-pulley-belt-tightener-mechanism/",
 "sheet_txt": "https://xemstudio.com/objects/jockey-pulley-belt-tightener-mechanism/sheet.txt",
 "sheet": {
  "basis": "Xem Studio design following Brown No. 5 (1868)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The belt is made a little long, so it slips idle on the pulleys; a pulley on a lever (the jockey or tightener) pressed on the back of the slack strand takes up the slack and the drive starts. Lift the lever and it stops — a clutch without moving the belt.",
   "Here Ø40 and Ø80 pulleys at 140 mm, a 16 × 1.5 belt of 472.33 mm (0.98 mm longer than an open belt) and a Ø30 jockey pressing the upper strand in 8 mm. The jockey also adds wrap on the small pulley: 169.91° instead of 196.43°.",
   "Brown's No. 5. Put the jockey on the slack side (here the upper strand when the small pulley drives clockwise).",
   "Parts (each has its own page): flanged-flat-pulley-40, flanged-flat-pulley-80, flanged-flat-pulley-30-bore6, flat-belt-16x1-5-jockey-drive-40-80-c140, jockey-lever-bore6, dowel-pins-metric.",
   "Brown's movement No. 5 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "pulleys",
     "Ø40 and Ø80 at 140 mm"
    ],
    [
     "jockey",
     "Ø30, 8 mm deflection"
    ],
    [
     "belt",
     "16 × 1.5, 472.33 mm"
    ],
    [
     "wrap on Ø40",
     "169.91°"
    ],
    [
     "lever",
     "51.48 mm + 40 mm handle"
    ]
   ]
  }
 },
 "sheet_text": "Jockey (tightening) pulley engaging a slack belt — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/jockey-pulley-belt-tightener-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)\nBasis: Xem Studio design following Brown No. 5 (1868)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The belt is made a little long, so it slips idle on the pulleys; a pulley on a lever (the jockey or tightener) pressed on the back of the slack strand takes up the slack and the drive starts. Lift the lever and it stops — a clutch without moving the belt.\n- Here Ø40 and Ø80 pulleys at 140 mm, a 16 × 1.5 belt of 472.33 mm (0.98 mm longer than an open belt) and a Ø30 jockey pressing the upper strand in 8 mm. The jockey also adds wrap on the small pulley: 169.91° instead of 196.43°.\n- Brown's No. 5. Put the jockey on the slack side (here the upper strand when the small pulley drives clockwise).\n- Parts (each has its own page): flanged-flat-pulley-40, flanged-flat-pulley-80, flanged-flat-pulley-30-bore6, flat-belt-16x1-5-jockey-drive-40-80-c140, jockey-lever-bore6, dowel-pins-metric.\n- Brown's movement No. 5 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.\n\nparameter  value\npulleys  Ø40 and Ø80 at 140 mm\njockey  Ø30, 8 mm deflection\nbelt  16 × 1.5, 472.33 mm\nwrap on Ø40  169.91°\nlever  51.48 mm + 40 mm handle\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. 5: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_005.html\n\nFree files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/jockey-pulley-belt-tightener-mechanism/index.json\nAPI: https://xemstudio.com/api/geometry?object=jockey-pulley-belt-tightener-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. 5: figure, his text and an animation",
   "url": "https://507movements.com/mm_005.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": [
  "flanged-flat-pulley-40",
  "flanged-flat-pulley-80",
  "flanged-flat-pulley-30-bore6",
  "flat-belt-16x1-5-jockey-drive-40-80-c140",
  "jockey-lever-bore6",
  "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 a jockey pulley start and stop a belt drive?",
   "a": "The belt is made a little long, so it slips idle on the pulleys; a pulley on a lever (the jockey or tightener) pressed on the back of the slack strand takes up the slack and the drive starts. Lift the lever and it stops — a clutch without moving the belt."
  }
 ],
 "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": "jockey-pulley-belt-tightener-mechanism-assembly",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "Xem Studio Design License",
   "step": "https://xemstudio.com/files/hardware/jockey-pulley-belt-tightener-mechanism/jockey-pulley-belt-tightener-mechanism-assembly.step",
   "stl": "https://xemstudio.com/files/hardware/jockey-pulley-belt-tightener-mechanism/jockey-pulley-belt-tightener-mechanism-assembly.stl",
   "note": "Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/jockey-pulley-belt-tightener-mechanism/index.md"
}