{
 "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": "ltd-displacer",
 "name": "LTD Stirling displacer Ø96 × 8 and Ø146 × 8",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Can & LTD engines",
 "year": null,
 "question": "What size displacer goes in a coffee-cup Stirling engine?",
 "tags": [
  "ltd",
  "displacer",
  "coffee cup",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "ltd stirling displacer size",
  "coffee cup stirling displacer",
  "96 mm displacer",
  "low temperature stirling displacer dimensions"
 ],
 "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/ltd-displacer/",
 "sheet_txt": "https://xemstudio.com/objects/ltd-displacer/sheet.txt",
 "sheet": {
  "basis": "Senft LTD rule: displacer diameter ≫ stroke; diameter = chamber bore − 4 (2 mm radial gap, designed)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The wide, thin displacer of the LTD engine: a solid disc Ø96 × 8 for the Ø100 chamber or Ø146 × 8 for the Ø150, with a Ø2 hole at x −5 (under the top plate's rod guide) for the 2 mm rod.",
   "The 2 mm radial gap to the chamber wall is designed: air passes round the edge as the displacer moves.",
   "In the 20 mm chamber it moves 10 mm; at Ø96 that sweeps about 72 mL."
  ],
  "table": {
   "columns": [
    "file",
    "diameter",
    "thickness",
    "chamber",
    "radial gap",
    "rod hole"
   ],
   "rows": [
    [
     "ltd-100-displacer",
     96,
     8,
     100,
     2,
     2
    ],
    [
     "ltd-150-displacer",
     146,
     8,
     150,
     2,
     2
    ]
   ]
  }
 },
 "sheet_text": "LTD Stirling displacer Ø96 × 8 and Ø146 × 8 — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/ltd-displacer/  (CC BY 4.0)\nBasis: Senft LTD rule: displacer diameter ≫ stroke; diameter = chamber bore − 4 (2 mm radial gap, designed)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The wide, thin displacer of the LTD engine: a solid disc Ø96 × 8 for the Ø100 chamber or Ø146 × 8 for the Ø150, with a Ø2 hole at x −5 (under the top plate's rod guide) for the 2 mm rod.\n- The 2 mm radial gap to the chamber wall is designed: air passes round the edge as the displacer moves.\n- In the 20 mm chamber it moves 10 mm; at Ø96 that sweeps about 72 mL.\n\nfile  diameter  thickness  chamber  radial gap  rod hole\nltd-100-displacer  96  8  100  2  2\nltd-150-displacer  146  8  150  2  2\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Stirling engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine\n- James R. Senft: An Introduction to Low Temperature Differential Stirling Engines — book — Moriya Press [verify license at link] — https://www.stirlingengine.com/\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/ltd-displacer/index.json\nAPI: https://xemstudio.com/api/geometry?object=ltd-displacer\n",
 "sources": [
  {
   "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": "James R. Senft",
   "title": "An Introduction to Low Temperature Differential Stirling Engines",
   "url": "https://www.stirlingengine.com/",
   "formats": [
    "book"
   ],
   "license": "Moriya Press",
   "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": [
  "ltd-chamber-ring",
  "ltd-top-plate",
  "ltd-bottom-plate",
  "list-ltd-coffee-cup"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "ltd-chamber-ring",
     "why": "inside the Ø100 / Ø150 bore, 2 mm radial gap"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "ltd-top-plate",
     "why": "its 2 mm rod runs in the top plate's Ø2 bore"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "brass-tube-ks",
     "why": "2 mm rod in the Ø2 hole"
    }
   ]
  }
 ],
 "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": "displacer rod hole",
   "exact": "Ø2",
   "mates": "2 mm rod",
   "fit": "press",
   "files": "ltd-100-displacer"
  },
  {
   "feature": "displacer rod hole",
   "exact": "Ø2",
   "mates": "2 mm rod",
   "fit": "press",
   "files": "ltd-150-displacer"
  },
  {
   "feature": "displacer to chamber gap",
   "exact": "2 radial (Ø D−4 in Ø D)",
   "mates": "chamber ring bore",
   "fit": "designed",
   "files": "ltd-100-displacer"
  },
  {
   "feature": "displacer to chamber gap",
   "exact": "2 radial (Ø D−4 in Ø D)",
   "mates": "chamber ring bore",
   "fit": "designed",
   "files": "ltd-150-displacer"
  }
 ],
 "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 size displacer for a coffee cup Stirling engine?",
   "a": "Ø96 × 8 in a Ø100 × 20 chamber at 10 mm stroke on the engine here; Ø146 × 8 in the Ø150 chamber."
  },
  {
   "q": "Why is an LTD displacer so wide and thin?",
   "a": "With a 15–20 K difference the pressure swing is small, so it needs a large area moved a short way with little friction."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "ltd-100-displacer",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-100-displacer.step",
   "stl": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-100-displacer.stl",
   "note": "displacer Ø96 × 8 with a Ø2 rod hole at x -5 under the top plate's guide (2 mm radial gap to the Ø100 chamber: designed)"
  },
  {
   "file": "ltd-150-displacer",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-150-displacer.step",
   "stl": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-150-displacer.stl",
   "note": "displacer Ø146 × 8 with a Ø2 rod hole at x -5 under the top plate's guide (2 mm radial gap to the Ø150 chamber: designed)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/ltd-displacer/index.md"
}