{
 "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": "rocker-beam",
 "name": "Rocker beam 60 / 80 / 100 mm on a 623 pivot",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "What are the dimensions of a rocker beam for a beam-driven Stirling engine?",
 "tags": [
  "rocker beam",
  "walking beam",
  "gamma",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "walking beam stirling",
  "rocker beam stirling displacer",
  "beam engine stirling"
 ],
 "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/rocker-beam/",
 "sheet_txt": "https://xemstudio.com/objects/rocker-beam/sheet.txt",
 "sheet": {
  "basis": "Centre pivot on a 623 bearing (Ø10 pocket, fit: press); Ø3 end holes (fit: run) at ±L/2",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The walking beam of a beam-driven gamma: one end to the crank's con-rod, the other to the displacer rod, pivoting in the middle.",
   "A 12 wide × 6 thick bar L + 12 long (72 / 92 / 112) with Ø3 holes at ±L/2 (fit: run) and a Ø10 pocket on centre for a 623 bearing (fit: press).",
   "With equal arms the ratio is 1:1: the displacer stroke equals the crank stroke."
  ],
  "table": {
   "columns": [
    "file",
    "pin centres",
    "length",
    "section",
    "pivot",
    "end holes"
   ],
   "rows": [
    [
     "rocker-beam-60",
     60,
     72,
     "12 × 6",
     "Ø10 (623)",
     "Ø3"
    ],
    [
     "rocker-beam-80",
     80,
     92,
     "12 × 6",
     "Ø10 (623)",
     "Ø3"
    ],
    [
     "rocker-beam-100",
     100,
     112,
     "12 × 6",
     "Ø10 (623)",
     "Ø3"
    ]
   ]
  }
 },
 "sheet_text": "Rocker beam 60 / 80 / 100 mm on a 623 pivot — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/rocker-beam/  (CC BY 4.0)\nBasis: Centre pivot on a 623 bearing (Ø10 pocket, fit: press); Ø3 end holes (fit: run) at ±L/2\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The walking beam of a beam-driven gamma: one end to the crank's con-rod, the other to the displacer rod, pivoting in the middle.\n- A 12 wide × 6 thick bar L + 12 long (72 / 92 / 112) with Ø3 holes at ±L/2 (fit: run) and a Ø10 pocket on centre for a 623 bearing (fit: press).\n- With equal arms the ratio is 1:1: the displacer stroke equals the crank stroke.\n\nfile  pin centres  length  section  pivot  end holes\nrocker-beam-60  60  72  12 × 6  Ø10 (623)  Ø3\nrocker-beam-80  80  92  12 × 6  Ø10 (623)  Ø3\nrocker-beam-100  100  112  12 × 6  Ø10 (623)  Ø3\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Beam engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Beam_engine\n- Wikipedia: Stirling engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine\n- Long Earth Society: Engine builds — 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/rocker-beam/index.json\nAPI: https://xemstudio.com/api/geometry?object=rocker-beam\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Beam engine",
   "url": "https://en.wikipedia.org/wiki/Beam_engine",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Stirling engine",
   "url": "https://en.wikipedia.org/wiki/Stirling_engine",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine builds",
   "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": [
  "beam-pivot-post",
  "tri-clamp-engine-base-plate",
  "ball-bearings-metric",
  "crank-discs-5mm-bore"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "beam-pivot-post",
     "why": "623 on the post's Ø3 pin"
    },
    {
     "slug": "ball-bearings-metric",
     "why": "623 in the Ø10 pocket"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "crank-discs-5mm-bore",
     "why": "con-rod on one Ø3 end"
    },
    {
     "slug": "rod-clevises",
     "why": "rod clevis on the other end"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "dowel-pins-metric",
     "why": "Ø3 pins"
    }
   ]
  }
 ],
 "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": "rocker-beam pivot pocket",
   "exact": "Ø10",
   "mates": "623 bearing",
   "fit": "press",
   "files": "rocker-beam-"
  },
  {
   "feature": "rocker-beam ends",
   "exact": "Ø3",
   "mates": "Ø3 pins (turn on them)",
   "fit": "run",
   "files": "rocker-beam-"
  }
 ],
 "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 a beam-driven Stirling engine?",
   "a": "The crank drives a rocker beam whose far end moves the displacer, so the crank can sit beside the cylinder."
  },
  {
   "q": "What bearing goes in the rocker beam?",
   "a": "A 623 (3 × 10 × 4) in the centre pocket, on the pivot post's Ø3 pin."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "rocker-beam-60",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/gamma-base-plate-and-beam/rocker-beam-60.step",
   "stl": "https://xemstudio.com/files/hardware/gamma-base-plate-and-beam/rocker-beam-60.stl",
   "note": "rocker beam 60 mm, centre pivot on a 623 (Ø10 pocket), Ø3 ends (beam-driven displacer)"
  },
  {
   "file": "rocker-beam-80",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/gamma-base-plate-and-beam/rocker-beam-80.step",
   "stl": "https://xemstudio.com/files/hardware/gamma-base-plate-and-beam/rocker-beam-80.stl",
   "note": "rocker beam 80 mm, centre pivot on a 623 (Ø10 pocket), Ø3 ends (beam-driven displacer)"
  },
  {
   "file": "rocker-beam-100",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/gamma-base-plate-and-beam/rocker-beam-100.step",
   "stl": "https://xemstudio.com/files/hardware/gamma-base-plate-and-beam/rocker-beam-100.stl",
   "note": "rocker beam 100 mm, centre pivot on a 623 (Ø10 pocket), Ø3 ends (beam-driven displacer)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/rocker-beam/index.md"
}