{
 "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": "rhombic-link",
 "name": "Rhombic drive link, 30 mm centres",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "How long are the links in a rhombic drive?",
 "tags": [
  "rhombic drive",
  "link",
  "linkage",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "rhombic drive link length",
  "rhombic link stl",
  "40 mm link 3 mm holes"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/rhombic-link/",
 "sheet_txt": "https://xemstudio.com/objects/rhombic-link/sheet.txt",
 "sheet": {
  "basis": "Rhombic kinematics (tools/rhombic_geom.py): four equal links L = 30 between crank pins at e = 7 on gears 66 apart and yoke pivots at ±12.7",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Four identical links join the two crank pins to the two yokes, forming the rhombus. Each is 30 mm between Ø3 holes (fit: run), 38 × 8 × 5 with round ends.",
   "Two ride each crank pin: the lower link next to the gear, the upper link outside it.",
   "Link length, gear centres, throw and yoke span together set the phase: here 90.0° with both strokes 20.12 mm."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "centres",
     30
    ],
    [
     "outline",
     "38 × 8 × 5"
    ],
    [
     "holes",
     "2 × Ø3 (run)"
    ],
    [
     "quantity",
     4
    ]
   ]
  }
 },
 "sheet_text": "Rhombic drive link, 30 mm centres — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/rhombic-link/  (CC BY 4.0)\nBasis: Rhombic kinematics (tools/rhombic_geom.py): four equal links L = 30 between crank pins at e = 7 on gears 66 apart and yoke pivots at ±12.7\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Four identical links join the two crank pins to the two yokes, forming the rhombus. Each is 30 mm between Ø3 holes (fit: run), 38 × 8 × 5 with round ends.\n- Two ride each crank pin: the lower link next to the gear, the upper link outside it.\n- Link length, gear centres, throw and yoke span together set the phase: here 90.0° with both strokes 20.12 mm.\n\nparameter  value\ncentres  30.0\noutline  38 × 8 × 5\nholes  2 × Ø3 (run)\nquantity  4\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Rhombic drive — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Rhombic_drive\n- Wikipedia: Stirling engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine\n- Philips Research / Meijer: The Philips Stirling engine (rhombic drive papers, 1958–1965) — web — reference [verify license at link] — https://en.wikipedia.org/wiki/Rhombic_drive#History\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, 1 parts): https://xemstudio.com/files/hardware/rhombic-link/index.json\nAPI: https://xemstudio.com/api/geometry?object=rhombic-link\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Rhombic drive",
   "url": "https://en.wikipedia.org/wiki/Rhombic_drive",
   "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": "Philips Research / Meijer",
   "title": "The Philips Stirling engine (rhombic drive papers, 1958–1965)",
   "url": "https://en.wikipedia.org/wiki/Rhombic_drive#History",
   "formats": [
    "web"
   ],
   "license": "reference",
   "license_verified": false,
   "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": [
  "rhombic-crank-gear",
  "rhombic-upper-yoke",
  "rhombic-lower-yoke",
  "dowel-pins-metric",
  "list-beta-rhombic-2in"
 ],
 "fits": [
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "rhombic-crank-gear",
     "why": "Ø3 hole on the gear's crank pin"
    },
    {
     "slug": "rhombic-upper-yoke",
     "why": "Ø3 pin at the yoke's ±12.7 pivots"
    },
    {
     "slug": "rhombic-lower-yoke",
     "why": "Ø3 pin at the yoke's ±12.7 pivots"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "dowel-pins-metric",
     "why": "Ø3 link 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": "link ends",
   "exact": "Ø3",
   "mates": "Ø3 pins (turn on them)",
   "fit": "run",
   "files": "link-"
  }
 ],
 "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": "How many links does a rhombic drive need?",
   "a": "Four equal links: two on each crank pin, one to the upper yoke and one to the lower."
  },
  {
   "q": "What link length goes with this rhombic drive?",
   "a": "30 mm centres, with a 7 mm throw, gears 66 apart and yoke pivots at ±12.7."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "link-30",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/rhombic-drive-kit/link-30.step",
   "stl": "https://xemstudio.com/files/hardware/rhombic-drive-kit/link-30.stl",
   "note": "rhombic link 30 mm centres, 8 wide × 5, Ø3 pivot holes; four per drive"
  }
 ],
 "markdown": "https://xemstudio.com/objects/rhombic-link/index.md"
}