{
 "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-crank-pin",
 "name": "Rhombic drive crank pin Ø3 × 17",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "What size crank pin does the rhombic drive gear take?",
 "tags": [
  "crank pin",
  "pin",
  "rhombic drive",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "rhombic crank pin",
  "3 x 14 pin",
  "3mm crank pin"
 ],
 "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-crank-pin/",
 "sheet_txt": "https://xemstudio.com/objects/rhombic-crank-pin/sheet.txt",
 "sheet": {
  "basis": "Ø3 pin at the gear's Ø3 crank-pin hole; 0.4 chamfer on one end; length = gear web + 1 mm + two links",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The crank pin pressed into each rhombic gear 7 mm off its axis: Ø3 × 17 with a 0.4 mm chamfer on one end.",
   "It runs from the gear web's back face through the web (6, fit: press), a 1 mm gap and the lower and upper links (5 each, fit: run), ending flush with the upper link."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "diameter",
     3
    ],
    [
     "length",
     17
    ],
    [
     "chamfer",
     0.4
    ]
   ]
  }
 },
 "sheet_text": "Rhombic drive crank pin Ø3 × 17 — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/rhombic-crank-pin/  (CC BY 4.0)\nBasis: Ø3 pin at the gear's Ø3 crank-pin hole; 0.4 chamfer on one end; length = gear web + 1 mm + two links\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The crank pin pressed into each rhombic gear 7 mm off its axis: Ø3 × 17 with a 0.4 mm chamfer on one end.\n- It runs from the gear web's back face through the web (6, fit: press), a 1 mm gap and the lower and upper links (5 each, fit: run), ending flush with the upper link.\n\nparameter  value\ndiameter  3\nlength  17.0\nchamfer  0.4\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-crank-pin/index.json\nAPI: https://xemstudio.com/api/geometry?object=rhombic-crank-pin\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-link",
  "dowel-pins-metric",
  "stirling-crankshafts"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "rhombic-crank-gear",
     "why": "pressed in the Ø3 hole at 7 mm"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "rhombic-link",
     "why": "two links turn on it"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "stirling-crankshafts",
     "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": "crank pin",
   "exact": "Ø3 × 17",
   "mates": "gear pin hole (press) and two link ends (run)",
   "fit": "press",
   "files": "crank-pin-"
  }
 ],
 "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 pin goes in the rhombic crank gear?",
   "a": "A Ø3 × 17 pin pressed into the Ø3 hole 7 mm off centre; two links turn on it."
  },
  {
   "q": "Why is the crank pin 17 mm long?",
   "a": "Gear web 6 + 1 mm gap + two 5 mm links: it ends flush with the outer link, short of the yokes' plane."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "crank-pin-3x17",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/rhombic-drive-kit/crank-pin-3x17.step",
   "stl": "https://xemstudio.com/files/hardware/rhombic-drive-kit/crank-pin-3x17.stl",
   "note": "Ø3 × 17 crank pin: through the gear web, a 1 mm gap, the lower and the upper link"
  }
 ],
 "markdown": "https://xemstudio.com/objects/rhombic-crank-pin/index.md"
}