{
 "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": "htd-flywheel-400",
 "name": "Ø400 flywheel on a Ø12 shaft",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Tri-clamp engine parts",
 "year": null,
 "question": "How big a flywheel does a slow large Stirling engine need?",
 "tags": [
  "flywheel",
  "htd",
  "stirling"
 ],
 "aliases": [
  "400 mm flywheel",
  "large stirling flywheel"
 ],
 "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/htd-flywheel-400/",
 "sheet_txt": "https://xemstudio.com/objects/htd-flywheel-400/sheet.txt",
 "sheet": {
  "basis": "Exact geometry",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Rim r 175..200 × 30 wide, 5 web, Ø50 × 40 hub, two M6 grubs. J = 0.104 kg·m² (3.9 kg) at 2.7 g/cm³, 0.305 kg·m² (11.3 kg) at 7.9 g/cm³.",
   "On the HTD it hangs outside the seal cap at x 186.5..226.5; a slow flat engine needs the inertia (the speed swing is on the list page)."
  ],
  "table": {
   "columns": [
    "od_mm",
    "rim_mm",
    "web_mm",
    "hub_mm",
    "J_kgm2_2.7",
    "J_kgm2_7.9"
   ],
   "rows": [
    [
     400,
     "175–200 × 30",
     5,
     "Ø50 × 40",
     0.104,
     0.305
    ]
   ]
  }
 },
 "sheet_text": "Ø400 flywheel on a Ø12 shaft — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/htd-flywheel-400/  (CC BY 4.0)\nBasis: Exact geometry\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Rim r 175..200 × 30 wide, 5 web, Ø50 × 40 hub, two M6 grubs. J = 0.104 kg·m² (3.9 kg) at 2.7 g/cm³, 0.305 kg·m² (11.3 kg) at 7.9 g/cm³.\n- On the HTD it hangs outside the seal cap at x 186.5..226.5; a slow flat engine needs the inertia (the speed swing is on the list page).\n\nod_mm  rim_mm  web_mm  hub_mm  J_kgm2_2.7  J_kgm2_7.9\n400.0  175–200 × 30  5.0  Ø50 × 40  0.104  0.305\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/htd-flywheel-400/index.json\nAPI: https://xemstudio.com/api/geometry?object=htd-flywheel-400\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-htd-10in",
  "htd-generator-drive"
 ],
 "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": "Ø12 × 40",
   "mates": "Ø12 shaft, two M6 grubs (drawn Ø6)",
   "fit": "slide",
   "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": "How heavy is it?",
   "a": "3.9 kg at 2.7 g/cm³, 11.3 kg at 7.9 g/cm³."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "flywheel-400-b12",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/htd-flywheel-400/flywheel-400-b12.step",
   "stl": "https://xemstudio.com/files/hardware/htd-flywheel-400/flywheel-400-b12.stl",
   "note": "Ø400 flywheel: rim r 175..200 × 30, web 5, hub Ø50 × 40, Ø12 bore, two M6 tapped radial holes"
  }
 ],
 "markdown": "https://xemstudio.com/objects/htd-flywheel-400/index.md"
}