{
 "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-displacers-10in",
 "name": "HTD displacers: Ø240 flat hollow displacers for a 10 in chamber",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Tri-clamp engine parts",
 "year": null,
 "question": "How do I make a large light displacer for a flat Stirling engine?",
 "tags": [
  "htd",
  "displacer",
  "flat displacer",
  "stirling",
  "ltd"
 ],
 "aliases": [
  "large stirling displacer",
  "flat plate stirling displacer",
  "ltd displacer dimensions"
 ],
 "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-displacers-10in/",
 "sheet_txt": "https://xemstudio.com/objects/htd-displacers-10in/sheet.txt",
 "sheet": {
  "basis": "Exact geometry: Ø240 shells in the 10 in bore (Ø247.19), 3.6 radial gap",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A thin closed shell: 0.5 skins top and bottom and a 0.5 rim, a Ø20 hub through the middle with the rod socket, a Ø1 hole in the top skin so the inside follows the mean pressure (the skins never carry the charge pressure, only the flow's few pascals).",
   "Mass about 0.57 kg at a density of 7.9 g/cm³ (a lighter shell material scales it). Gap to the bore 3.6 radial: the annulus is the only passage between hot and cold space and the shuttle-loss path (0.5 W air, 2.4 W helium, Martini).",
   "Heat leaks through the displacer: the rim skin about 44 W and radiation between the skins about 71 W (ε 0.3, no shield); a foil shield inside cuts the radiation."
  ],
  "table": {
   "columns": [
    "part",
    "diameter_mm",
    "thickness_mm",
    "stroke_mm",
    "socket_mm"
   ],
   "rows": [
    [
     "displacer-240x40-rod6",
     240,
     40,
     8,
     30
    ]
   ]
  }
 },
 "sheet_text": "HTD displacers: Ø240 flat hollow displacers for a 10 in chamber — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/htd-displacers-10in/  (CC BY 4.0)\nBasis: Exact geometry: Ø240 shells in the 10 in bore (Ø247.19), 3.6 radial gap\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A thin closed shell: 0.5 skins top and bottom and a 0.5 rim, a Ø20 hub through the middle with the rod socket, a Ø1 hole in the top skin so the inside follows the mean pressure (the skins never carry the charge pressure, only the flow's few pascals).\n- Mass about 0.57 kg at a density of 7.9 g/cm³ (a lighter shell material scales it). Gap to the bore 3.6 radial: the annulus is the only passage between hot and cold space and the shuttle-loss path (0.5 W air, 2.4 W helium, Martini).\n- Heat leaks through the displacer: the rim skin about 44 W and radiation between the skins about 71 W (ε 0.3, no shield); a foil shield inside cuts the radiation.\n\npart  diameter_mm  thickness_mm  stroke_mm  socket_mm\ndisplacer-240x40-rod6  240.0  40.0  8.0  30.0\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- NASA (NTRS, public domain): W. R. Martini, Stirling Engine Design Manual, NASA CR-168088 (1983): shuttle loss — PDF — US Government work, public domain — https://ntrs.nasa.gov/citations/19830022057\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-displacers-10in/index.json\nAPI: https://xemstudio.com/api/geometry?object=htd-displacers-10in\n",
 "sources": [
  {
   "publisher": "NASA (NTRS, public domain)",
   "title": "W. R. Martini, Stirling Engine Design Manual, NASA CR-168088 (1983): shuttle loss",
   "url": "https://ntrs.nasa.gov/citations/19830022057",
   "formats": [
    "PDF"
   ],
   "license": "US Government work, public domain",
   "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": [
  "list-htd-10in",
  "htd-hot-cup-10in",
  "htd-displacer-rods"
 ],
 "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": "OD",
   "exact": "Ø240 in the Ø247.19 bore",
   "mates": "hot cup bore (3.6 radial, no contact)",
   "fit": "designed",
   "files": "all"
  },
  {
   "feature": "rod socket",
   "exact": "Ø6 × 30 (M6 as the major diameter)",
   "mates": "displacer rod, M6 thread",
   "fit": "press",
   "files": "all"
  },
  {
   "feature": "end clearance",
   "exact": "1.5 to floor and ceiling at the stroke ends",
   "mates": "cup floor, cap",
   "fit": "designed",
   "files": "all"
  },
  {
   "feature": "equalising hole",
   "exact": "Ø1",
   "mates": "gas (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 displacer hollow with a hole?",
   "a": "Light, and the hole lets its inside follow the mean pressure, so a charged engine does not crush it."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "displacer-240x40-rod6",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/htd-displacers-10in/displacer-240x40-rod6.step",
   "stl": "https://xemstudio.com/files/hardware/htd-displacers-10in/displacer-240x40-rod6.stl",
   "note": "Ø240 × 40 hollow displacer: 0.5 skins and rim, Ø20 hub, Ø6 rod socket 30 deep (M6 thread as the plain bore), Ø1 equalising hole"
  }
 ],
 "markdown": "https://xemstudio.com/objects/htd-displacers-10in/index.md"
}