{
 "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-crankcase-flywheel",
 "name": "Crankcase flywheels: Ø44 × 12 disc and Ø42 pocket flywheel on a Ø3 shaft, inside a 2 in tri-clamp fitting",
 "kind": "hardware",
 "category": "Hardware",
 "group": "Stirling & thermoacoustic",
 "year": null,
 "question": "Where does the flywheel go on a Stirling engine with no shaft out of its crankcase?",
 "tags": [
  "flywheel",
  "crankshaft",
  "disc",
  "sealed",
  "tri-clamp",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "internal flywheel stirling",
  "flywheel inside crankcase",
  "small flywheel disc 44 mm"
 ],
 "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-crankcase-flywheel/",
 "sheet_txt": "https://xemstudio.com/objects/tri-clamp-crankcase-flywheel/sheet.txt",
 "sheet": {
  "basis": "Design values: Ø44 so the disc turns inside the 2 in bore (Ø47.5); Ø42 so the pocket flywheel turns in the bearing plate's Ø44 pocket inside the gasket lip (Ø45.3); inertia and the cycle's energy swing from the Schmidt estimate",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Discs on the crankshaft between the crank and the bearing plates' spigots (one on +X, one on −X beside the crank gear), and a pocket flywheel on each shaft end in the bearing plate's pocket, 0.5 mm from the end cap. An M3 grub holds each.",
   "Why: nothing turns outside the vessel, so these, the crank gear and the generator's can (which turns 2.8 times faster, so counts 7.8 times its own inertia) are the whole flywheel. One cycle swings about 0.16 J against a steady load: a speed swing of 12–27 % at 900 rpm and 7–15 % at 1200 rpm for a disc density of 7.8 to 2.7 g/cm³ (the motor's turning part taken as 18 g at r 12.5)."
  ],
  "table": {
   "columns": [
    "file",
    "size",
    "bore",
    "per engine"
   ],
   "rows": [
    [
     "crank-flywheel-44x12-b3",
     "Ø44 × 12",
     "Ø3, radial M3 grub",
     2
    ],
    [
     "pocket-flywheel-42x8-b3",
     "Ø42 × 8 + Ø10 hub",
     "Ø3, M3 grub",
     2
    ]
   ]
  }
 },
 "sheet_text": "Crankcase flywheels: Ø44 × 12 disc and Ø42 pocket flywheel on a Ø3 shaft, inside a 2 in tri-clamp fitting — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/tri-clamp-crankcase-flywheel/  (CC BY 4.0)\nBasis: Design values: Ø44 so the disc turns inside the 2 in bore (Ø47.5); Ø42 so the pocket flywheel turns in the bearing plate's Ø44 pocket inside the gasket lip (Ø45.3); inertia and the cycle's energy swing from the Schmidt estimate\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Discs on the crankshaft between the crank and the bearing plates' spigots (one on +X, one on −X beside the crank gear), and a pocket flywheel on each shaft end in the bearing plate's pocket, 0.5 mm from the end cap. An M3 grub holds each.\n- Why: nothing turns outside the vessel, so these, the crank gear and the generator's can (which turns 2.8 times faster, so counts 7.8 times its own inertia) are the whole flywheel. One cycle swings about 0.16 J against a steady load: a speed swing of 12–27 % at 900 rpm and 7–15 % at 1200 rpm for a disc density of 7.8 to 2.7 g/cm³ (the motor's turning part taken as 18 g at r 12.5).\n\nfile  size  bore  per engine\ncrank-flywheel-44x12-b3  Ø44 × 12  Ø3, radial M3 grub  2\npocket-flywheel-42x8-b3  Ø42 × 8 + Ø10 hub  Ø3, M3 grub  2\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Ohio University (I. Urieli): Stirling cycle machine analysis: the Schmidt (isothermal) analysis — web — university course pages [verify license at link] — https://www.ohio.edu/mechanical/stirling/isothermal/Schmidt.html\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-crankcase-flywheel/index.json\nAPI: https://xemstudio.com/api/geometry?object=tri-clamp-crankcase-flywheel\n",
 "sources": [
  {
   "publisher": "Ohio University (I. Urieli)",
   "title": "Stirling cycle machine analysis: the Schmidt (isothermal) analysis",
   "url": "https://www.ohio.edu/mechanical/stirling/isothermal/Schmidt.html",
   "formats": [
    "web"
   ],
   "license": "university course pages",
   "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": [
  "tri-clamp-generator-step-up-gears",
  "tri-clamp-clamp-in-bearing-plate",
  "tri-clamp-cross-crank-webs",
  "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": "bore",
   "exact": "Ø3",
   "mates": "Ø3 crankshaft (M3 grub)",
   "fit": "slide",
   "files": "all"
  },
  {
   "feature": "grub hole",
   "exact": "Ø2.5 (M3 tapped), radial from the rim",
   "mates": "set-m3x10",
   "fit": "designed",
   "files": "crank-flywheel-"
  },
  {
   "feature": "grub hole",
   "exact": "Ø2.5 (M3 tapped) in the hub",
   "mates": "set-m3x3",
   "fit": "designed",
   "files": "pocket-flywheel-"
  },
  {
   "feature": "rim",
   "exact": "Ø44 / Ø42",
   "mates": "2 in bore Ø47.5 / plate pocket Ø44 and gasket lip Ø45.3 (no contact)",
   "fit": "designed",
   "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 is the flywheel inside?",
   "a": "Nothing turns outside the vessel: the discs, the pocket flywheels, the crank gear and the generator's can are the whole flywheel."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "crank-flywheel-44x12-b3",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-crankcase-flywheel/crank-flywheel-44x12-b3.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-crankcase-flywheel/crank-flywheel-44x12-b3.stl",
   "note": "crankcase flywheel disc Ø44 × 12, Ø3 bore, radial M3 tapped hole (Ø2.5) from the rim to the bore at mid-thickness"
  },
  {
   "file": "pocket-flywheel-42x8-b3",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-crankcase-flywheel/pocket-flywheel-42x8-b3.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-crankcase-flywheel/pocket-flywheel-42x8-b3.stl",
   "note": "pocket flywheel Ø42 × 8 on a Ø10 × 12.9 hub, Ø3 bore, M3 grub hole (Ø2.5) in the hub: turns in the bearing plate's Ø44 pocket"
  }
 ],
 "markdown": "https://xemstudio.com/objects/tri-clamp-crankcase-flywheel/index.md"
}