{
 "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": "eccentric-sheaves",
 "name": "Eccentric sheaves Ø30 at 3, 5 and 8 mm offset",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "What is the stroke of an eccentric sheave?",
 "tags": [
  "eccentric",
  "sheave",
  "cam",
  "rotary to linear",
  "mechanism",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "eccentric sheave",
  "eccentric cam 5mm shaft",
  "eccentric drive",
  "eccentric stroke"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 3,
 "url": "https://xemstudio.com/objects/eccentric-sheaves/",
 "sheet_txt": "https://xemstudio.com/objects/eccentric-sheaves/sheet.txt",
 "sheet": {
  "basis": "Disc on a shaft offset e from its centre; stroke = 2e",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A Ø30 × 8 disc with a Ø5 shaft hole offset 3, 5 or 8 mm from its centre: 6, 10 or 16 mm stroke.",
   "A radial Ø2.5 hole (M3 tap drill) at mid-thickness locks it to the shaft.",
   "It turns inside the Ø30 strap, which carries the load round its whole bore; it sits anywhere along a straight shaft without a crank throw."
  ],
  "table": {
   "columns": [
    "file",
    "offset e",
    "stroke",
    "disc",
    "shaft"
   ],
   "rows": [
    [
     "eccentric-d30-e3",
     3,
     6,
     "Ø30 × 8",
     5
    ],
    [
     "eccentric-d30-e5",
     5,
     10,
     "Ø30 × 8",
     5
    ],
    [
     "eccentric-d30-e8",
     8,
     16,
     "Ø30 × 8",
     5
    ]
   ]
  }
 },
 "sheet_text": "Eccentric sheaves Ø30 at 3, 5 and 8 mm offset — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/eccentric-sheaves/  (CC BY 4.0)\nBasis: Disc on a shaft offset e from its centre; stroke = 2e\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A Ø30 × 8 disc with a Ø5 shaft hole offset 3, 5 or 8 mm from its centre: 6, 10 or 16 mm stroke.\n- A radial Ø2.5 hole (M3 tap drill) at mid-thickness locks it to the shaft.\n- It turns inside the Ø30 strap, which carries the load round its whole bore; it sits anywhere along a straight shaft without a crank throw.\n\nfile  offset e  stroke  disc  shaft\neccentric-d30-e3  3  6  Ø30 × 8  5\neccentric-d30-e5  5  10  Ø30 × 8  5\neccentric-d30-e8  8  16  Ø30 × 8  5\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Eccentric (mechanism) — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Eccentric_(mechanism)\n- Long Earth Society: Engine and rig builds on extrusion frames — web, video — LES site — https://longearthsociety.com/engineering/\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 3 parts): https://xemstudio.com/files/hardware/eccentric-sheaves/index.json\nAPI: https://xemstudio.com/api/geometry?object=eccentric-sheaves\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Eccentric (mechanism)",
   "url": "https://en.wikipedia.org/wiki/Eccentric_(mechanism)",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine and rig builds on extrusion frames",
   "url": "https://longearthsociety.com/engineering/",
   "formats": [
    "web",
    "video"
   ],
   "license": "LES site",
   "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-strap",
  "metric-shafts",
  "crank-discs-5mm-bore",
  "scotch-yoke",
  "swash-plate-40mm"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "metric-shafts",
     "why": "Ø5 shaft, M3 grub"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "eccentric-strap",
     "why": "Ø30 disc in the Ø30 strap bore"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "crank-discs-5mm-bore",
     "why": "crank and con-rod"
    },
    {
     "slug": "scotch-yoke",
     "why": "sine motion"
    }
   ]
  }
 ],
 "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": [
  {
   "feature": "eccentric bore",
   "exact": "Ø5",
   "mates": "Ø5 shaft",
   "fit": "slide",
   "files": "eccentric-d30-e"
  },
  {
   "feature": "set-screw hole",
   "exact": "Ø2.5",
   "mates": "M3 tap drill",
   "fit": "designed",
   "files": "eccentric-d30-e"
  }
 ],
 "fit_classes": {
  "press": "stays put: pin, tube, bearing or magnet held by interference. Typical FDM: hole +0.0 to +0.1 mm on diameter.",
  "slide": "assembles by hand and is held by a grub, pinch or clamp: shaft in a hub, rod in a socket, spigot in a bore. Typical FDM: +0.2 mm.",
  "run": "turns or slides in use: pin in a link, rod through a guide. Typical FDM: +0.3 mm.",
  "socket": "large sliding fit: syringe barrel, sleeve, bobbin in a bore. Typical FDM: +0.3 mm.",
  "clamp": "split part that closes on the mating part with screws: make it at size.",
  "designed": "a gap that is part of the design (piston fit option, displacer gap, air gap): do not change."
 },
 "faq": [
  {
   "q": "What is the stroke of an eccentric?",
   "a": "Twice the offset: the 5 mm eccentric gives 10 mm."
  },
  {
   "q": "Why an eccentric instead of a crank?",
   "a": "It sits anywhere on a straight shaft with no throw, and the strap bears all the way round."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "eccentric-d30-e3",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/eccentric-and-strap/eccentric-d30-e3.step",
   "stl": "https://xemstudio.com/files/hardware/eccentric-and-strap/eccentric-d30-e3.stl",
   "note": "eccentric Ø30, 3 mm offset (6 mm stroke), Ø5 shaft, Ø2.5 set-screw hole"
  },
  {
   "file": "eccentric-d30-e5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/eccentric-and-strap/eccentric-d30-e5.step",
   "stl": "https://xemstudio.com/files/hardware/eccentric-and-strap/eccentric-d30-e5.stl",
   "note": "eccentric Ø30, 5 mm offset (10 mm stroke), Ø5 shaft, Ø2.5 set-screw hole"
  },
  {
   "file": "eccentric-d30-e8",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/eccentric-and-strap/eccentric-d30-e8.step",
   "stl": "https://xemstudio.com/files/hardware/eccentric-and-strap/eccentric-d30-e8.stl",
   "note": "eccentric Ø30, 8 mm offset (16 mm stroke), Ø5 shaft, Ø2.5 set-screw hole"
  }
 ],
 "markdown": "https://xemstudio.com/objects/eccentric-sheaves/index.md"
}