{
 "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": "marble-engine-rocking-link",
 "name": "Rocking link 170 mm (crank to rocker)",
 "kind": "hardware",
 "category": "Hardware",
 "group": "Stirling & thermoacoustic",
 "year": null,
 "question": "What rocks the test tube of a marble Stirling engine?",
 "tags": [
  "marble engine",
  "link",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "marble engine connecting rod"
 ],
 "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/marble-engine-rocking-link/",
 "sheet_txt": "https://xemstudio.com/objects/marble-engine-rocking-link/sheet.txt",
 "sheet": {
  "basis": "My geometry: same section as the pin-end con-rods (8 × 5, Ø3 ends)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "170 mm between Ø3 holes; from the crank pin that leads the power pin by 90° to the rocker's lever pin. Length chosen so the rocker's mean angle is level."
  ],
  "table": {
   "columns": [
    "feature",
    "value_mm"
   ],
   "rows": [
    [
     "centres",
     170
    ],
    [
     "section",
     "8 × 5"
    ],
    [
     "holes",
     "Ø3"
    ]
   ]
  }
 },
 "sheet_text": "Rocking link 170 mm (crank to rocker) — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/marble-engine-rocking-link/  (CC BY 4.0)\nBasis: My geometry: same section as the pin-end con-rods (8 × 5, Ø3 ends)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- 170 mm between Ø3 holes; from the crank pin that leads the power pin by 90° to the rocker's lever pin. Length chosen so the rocker's mean angle is level.\n\nfeature  value_mm\ncentres  170.0\nsection  8 × 5\nholes  Ø3\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\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/marble-engine-rocking-link/index.json\nAPI: https://xemstudio.com/api/geometry?object=marble-engine-rocking-link\n",
 "sources": [
  {
   "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": [
  "list-test-tube-marble-engine",
  "borosilicate-test-tubes",
  "glass-marbles",
  "glass-syringes",
  "rubber-stoppers",
  "beam-pivot-post"
 ],
 "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": [
  {
   "feature": "end holes",
   "exact": "Ø3",
   "mates": "dowel-3x12 crank pin and lever pin (turn in them)",
   "fit": "run",
   "files": "all"
  }
 ],
 "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": "Why 170 mm?",
   "a": "It reaches from the crank to the rocker's lever pin 45 below the pivot, so the 7.5 mm crank throw rocks the tube -7.9° to +7.9°, and it sets the crank where the plunger never bottoms."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "rocking-link-170",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/marble-engine-rocking-link/rocking-link-170.step",
   "stl": "https://xemstudio.com/files/hardware/marble-engine-rocking-link/rocking-link-170.stl",
   "note": "rocking link, 170 mm centres, Ø3 holes, 8 wide × 5 thick: crank pin to the rocker's lever pin"
  }
 ],
 "markdown": "https://xemstudio.com/objects/marble-engine-rocking-link/index.md"
}