{
 "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-lower-yoke",
 "name": "Rhombic drive lower yoke, 25.4 mm pivot span",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "What are the dimensions of the piston yoke in a rhombic drive?",
 "tags": [
  "rhombic drive",
  "yoke",
  "piston",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "rhombic lower yoke",
  "rhombic piston yoke",
  "rhombic drive piston rod tube"
 ],
 "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-lower-yoke/",
 "sheet_txt": "https://xemstudio.com/objects/rhombic-lower-yoke/sheet.txt",
 "sheet": {
  "basis": "Yoke pivots at ±12.7 (rhombic kinematics, tools/rhombic_geom.py), pivot axes parallel to the gear shafts, rod axis across them; bore at the rod, M3 tap drill Ø2.5",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The lower yoke of the rhombus: a 35.4 × 10 bar, 6 thick along the gear-shaft direction, with Ø3 pivot holes (fit: run) at ±12.7 running parallel to the gear shafts.",
   "A Ø13 × 16 boss on the rod axis (across the pivots) holds the 5 mm tube piston rod (Ø5 bore through; the Ø3 displacer rod runs on up inside it) (fit: slide), with an M3 grub (Ø2.5 tapped) entering at mid-height; an M3 × 4 grub sits flush.",
   "Both yokes sit in one plane on the rod axis, in front of the two link planes; the lower-yoke pivot pins are Ø3 × 16."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "pivot span",
     25.4
    ],
    [
     "bar",
     "35.4 × 10 × 6"
    ],
    [
     "pivots",
     "2 × Ø3 (run), along the gear-shaft direction"
    ],
    [
     "boss",
     "Ø13 × 16"
    ],
    [
     "rod bore",
     "Ø5 through"
    ],
    [
     "grub hole",
     "Ø2.5 (M3)"
    ]
   ]
  }
 },
 "sheet_text": "Rhombic drive lower yoke, 25.4 mm pivot span — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/rhombic-lower-yoke/  (CC BY 4.0)\nBasis: Yoke pivots at ±12.7 (rhombic kinematics, tools/rhombic_geom.py), pivot axes parallel to the gear shafts, rod axis across them; bore at the rod, M3 tap drill Ø2.5\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The lower yoke of the rhombus: a 35.4 × 10 bar, 6 thick along the gear-shaft direction, with Ø3 pivot holes (fit: run) at ±12.7 running parallel to the gear shafts.\n- A Ø13 × 16 boss on the rod axis (across the pivots) holds the 5 mm tube piston rod (Ø5 bore through; the Ø3 displacer rod runs on up inside it) (fit: slide), with an M3 grub (Ø2.5 tapped) entering at mid-height; an M3 × 4 grub sits flush.\n- Both yokes sit in one plane on the rod axis, in front of the two link planes; the lower-yoke pivot pins are Ø3 × 16.\n\nparameter  value\npivot span  25.4\nbar  35.4 × 10 × 6\npivots  2 × Ø3 (run), along the gear-shaft direction\nboss  Ø13 × 16\nrod bore  Ø5 through\ngrub hole  Ø2.5 (M3)\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-lower-yoke/index.json\nAPI: https://xemstudio.com/api/geometry?object=rhombic-lower-yoke\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-upper-yoke",
  "rhombic-link",
  "brass-tube-ks",
  "tri-clamp-power-piston",
  "list-beta-rhombic-2in"
 ],
 "fits": [
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "brass-tube-ks",
     "why": "5 mm tube piston rod in the Ø5 bore"
    },
    {
     "slug": "tri-clamp-power-piston",
     "why": "the piston at the other end of the tube rod"
    },
    {
     "slug": "tri-clamp-flexure-head",
     "why": "piston plug carries the tube rod"
    },
    {
     "slug": "rhombic-link",
     "why": "two links on the ±12.7 Ø3 pivots"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "set-screws-metric",
     "why": "M3 clamp screw"
    }
   ]
  }
 ],
 "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": "yoke pivots",
   "exact": "Ø3",
   "mates": "Ø3 pins (turn on them)",
   "fit": "run",
   "files": "yoke-"
  },
  {
   "feature": "yoke rod bore",
   "exact": "Ø3 / Ø5",
   "mates": "displacer rod / 5 mm tube (M3 clamp)",
   "fit": "slide",
   "files": "yoke-"
  },
  {
   "feature": "yoke clamp screw hole",
   "exact": "Ø2.5",
   "mates": "M3 tap drill",
   "fit": "designed",
   "files": "yoke-"
  },
  {
   "feature": "lower-yoke bore",
   "exact": "Ø5 through",
   "mates": "5 mm tube (M3 clamp); displacer rod runs inside the tube",
   "fit": "slide",
   "files": "yoke-lower-"
  }
 ],
 "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 does the lower yoke of a rhombic drive hold?",
   "a": "The 5 mm tube piston rod, clamped by an M3 grub in its Ø13 boss; two links pivot on it at ±12.7."
  },
  {
   "q": "Which way do the yoke pivot holes run?",
   "a": "Parallel to the gear shafts, across the rod: the links swing in planes square to the shafts."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "yoke-lower-piston",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/rhombic-drive-kit/yoke-lower-piston.step",
   "stl": "https://xemstudio.com/files/hardware/rhombic-drive-kit/yoke-lower-piston.stl",
   "note": "lower yoke: as the upper, Ø13 × 16 boss with a Ø5 bore through for the 5 mm tube piston rod (M3 grub); the Ø3 displacer rod runs on up inside it"
  }
 ],
 "markdown": "https://xemstudio.com/objects/rhombic-lower-yoke/index.md"
}