{
 "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": "tri-clamp-diaphragm-crosshead",
 "name": "Diaphragm crosshead hub and tapped backing disc: 2 in, with the displacer rod through the centre",
 "kind": "hardware",
 "category": "Hardware",
 "group": "Stirling & thermoacoustic",
 "year": null,
 "question": "How do I drive a diaphragm from a crank when the displacer rod passes through its centre?",
 "tags": [
  "crosshead",
  "diaphragm",
  "rod guide",
  "bleed",
  "disc",
  "tri-clamp",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "diaphragm crosshead",
  "rod through diaphragm guide",
  "stirling bleed bore",
  "diaphragm con rod hub"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 2,
 "url": "https://xemstudio.com/objects/tri-clamp-diaphragm-crosshead/",
 "sheet_txt": "https://xemstudio.com/objects/tri-clamp-diaphragm-crosshead/sheet.txt",
 "sheet": {
  "basis": "Design values from the sealed generator: Ø20 centre clamp as the stock 2 in diaphragm disc, M2 screws (ISO 4762) in ISO 273 medium clearance holes and Ø1.6 tap-drill holes, Ø3 guide bore; the pin height comes from the crank layout",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The hub clamps the membrane from the crankcase side: a Ø20 × 3 disc with three Ø2.4 holes on Ø13 for M2 × 6 screws, heads up. Under the membrane the backing disc (Ø20 × 2, Ø5 centre hole) has three Ø1.6 holes tapped M2, so nothing stands below it into the working space.",
   "A Ø8 boss rises to 15 mm with a Ø3 bore straight through disc and boss: the displacer rod runs in it. This 15 mm close running fit is the only way for gas between the working space and the crankcase, the bleed that lets the crankcase follow the working space's mean pressure.",
   "A bar (z 5.5–9.5, 6 wide) runs out along +X to an arm at x 13.5–18.5 that carries the con-rod pin (Ø3 × 10, pressed) along X, 29.25 mm above the membrane face. The con-rod eye sits at x 8–13, beside the displacer's rod clevis (x ±6), so the two drives pass each other without touching.",
   "Fits: Ø3 bore run on the Ø3 rod (the bleed); pin hole press on the dowel; disc and backing clamp the membrane."
  ],
  "table": {
   "columns": [
    "part",
    "feature",
    "value"
   ],
   "rows": [
    [
     "hub",
     "disc",
     "Ø20 × 3, 3 × Ø2.4 on Ø13"
    ],
    [
     "hub",
     "guide bore",
     "Ø3 × 15 (run)"
    ],
    [
     "hub",
     "con-rod pin",
     "Ø3 along X at z 29.25, x 8.5–18.5"
    ],
    [
     "backing",
     "disc",
     "Ø20 × 2, Ø5 centre hole"
    ],
    [
     "backing",
     "screw holes",
     "3 × Ø1.6 (M2 tapped)"
    ]
   ]
  }
 },
 "sheet_text": "Diaphragm crosshead hub and tapped backing disc: 2 in, with the displacer rod through the centre — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/tri-clamp-diaphragm-crosshead/  (CC BY 4.0)\nBasis: Design values from the sealed generator: Ø20 centre clamp as the stock 2 in diaphragm disc, M2 screws (ISO 4762) in ISO 273 medium clearance holes and Ø1.6 tap-drill holes, Ø3 guide bore; the pin height comes from the crank layout\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The hub clamps the membrane from the crankcase side: a Ø20 × 3 disc with three Ø2.4 holes on Ø13 for M2 × 6 screws, heads up. Under the membrane the backing disc (Ø20 × 2, Ø5 centre hole) has three Ø1.6 holes tapped M2, so nothing stands below it into the working space.\n- A Ø8 boss rises to 15 mm with a Ø3 bore straight through disc and boss: the displacer rod runs in it. This 15 mm close running fit is the only way for gas between the working space and the crankcase, the bleed that lets the crankcase follow the working space's mean pressure.\n- A bar (z 5.5–9.5, 6 wide) runs out along +X to an arm at x 13.5–18.5 that carries the con-rod pin (Ø3 × 10, pressed) along X, 29.25 mm above the membrane face. The con-rod eye sits at x 8–13, beside the displacer's rod clevis (x ±6), so the two drives pass each other without touching.\n- Fits: Ø3 bore run on the Ø3 rod (the bleed); pin hole press on the dowel; disc and backing clamp the membrane.\n\npart  feature  value\nhub  disc  Ø20 × 3, 3 × Ø2.4 on Ø13\nhub  guide bore  Ø3 × 15 (run)\nhub  con-rod pin  Ø3 along X at z 29.25, x 8.5–18.5\nbacking  disc  Ø20 × 2, Ø5 centre hole\nbacking  screw holes  3 × Ø1.6 (M2 tapped)\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- ISO: ISO 273 clearance holes for bolts and screws (fine / medium / coarse) — standard — dimensions are facts [verify license at link] — https://www.iso.org/standard/4196.html\n- Wikipedia: Hagen–Poiseuille equation: plane Poiseuille flow between parallel plates (annular clearance leakage Q = π D δ³ Δp / 12 μ L) — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation\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, 2 parts): https://xemstudio.com/files/hardware/tri-clamp-diaphragm-crosshead/index.json\nAPI: https://xemstudio.com/api/geometry?object=tri-clamp-diaphragm-crosshead\n",
 "sources": [
  {
   "publisher": "ISO",
   "title": "ISO 273 clearance holes for bolts and screws (fine / medium / coarse)",
   "url": "https://www.iso.org/standard/4196.html",
   "formats": [
    "standard"
   ],
   "license": "dimensions are facts",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Hagen–Poiseuille equation: plane Poiseuille flow between parallel plates (annular clearance leakage Q = π D δ³ Δp / 12 μ L)",
   "url": "https://en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation",
   "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": [
  "tri-clamp-through-rod-membrane",
  "tri-clamp-diaphragm-disc",
  "rod-clevises",
  "connecting-rods-623",
  "dowel-pins-metric",
  "list-tri-clamp-sealed-diaphragm-generator"
 ],
 "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": "guide bore",
   "exact": "Ø3 × 15",
   "mates": "Ø3 displacer rod (crankshaft-3x60): the bleed between working space and crankcase",
   "fit": "run",
   "files": "crosshead-"
  },
  {
   "feature": "con-rod pin hole",
   "exact": "Ø3 along X in the arm",
   "mates": "dowel-3x10",
   "fit": "press",
   "files": "crosshead-"
  },
  {
   "feature": "screw holes",
   "exact": "3 × Ø2.4 on Ø13",
   "mates": "M2 × 6 (ISO 273 medium clearance)",
   "fit": "designed",
   "files": "crosshead-"
  },
  {
   "feature": "tapped holes",
   "exact": "3 × Ø1.6 (M2 tap drill) on Ø13",
   "mates": "shcs-m2x6",
   "fit": "designed",
   "files": "backing-"
  },
  {
   "feature": "centre hole",
   "exact": "Ø5",
   "mates": "Ø3 displacer rod (no contact)",
   "fit": "designed",
   "files": "backing-"
  }
 ],
 "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": "Where does gas pass between the working space and the crankcase?",
   "a": "Only along the Ø3 rod in the hub's 15 mm bore. With 5 µm radial clearance the mean pressures settle with a time constant of about 8 min; with 10 µm about 64 s. A cycle's leakage is negligible either way."
  },
  {
   "q": "Why is the con-rod pin on an arm at the side?",
   "a": "The displacer rod runs up the axis through the hub, so the diaphragm's con-rod has its own plane beside the displacer's clevis."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "crosshead-2in-p29.25",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-diaphragm-crosshead/crosshead-2in-p29.25.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-diaphragm-crosshead/crosshead-2in-p29.25.stl",
   "note": "crosshead hub: Ø20 × 3 disc with 3 × Ø2.4 on Ø13, Ø8 boss to 15, Ø3 bore 15 long (rod guide and bleed), bar z 5.5–9.5 to an arm x 13.5–18.5, Ø3 pin hole along X at 29.25"
  },
  {
   "file": "backing-2in-m2-tapped",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-diaphragm-crosshead/backing-2in-m2-tapped.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-diaphragm-crosshead/backing-2in-m2-tapped.stl",
   "note": "tapped backing disc Ø20 × 2: Ø5 centre hole, 3 × Ø1.6 (M2 tap drill) on Ø13"
  }
 ],
 "markdown": "https://xemstudio.com/objects/tri-clamp-diaphragm-crosshead/index.md"
}