{
 "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-coffee-cup-engine-kit",
 "name": "LTD (low-temperature differential, coffee-cup) Stirling kit: plates, chamber ring, displacer, top plate with syringe cylinder",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Can & LTD engines",
 "year": null,
 "question": "How do I build a coffee cup Stirling engine and what are the plate and displacer dimensions?",
 "tags": [
  "ltd",
  "low temperature differential",
  "coffee cup",
  "stirling",
  "senft",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "coffee cup stirling engine",
  "ltd stirling engine plans",
  "low temperature stirling dimensions",
  "senft ltd stirling",
  "hand warmed stirling engine",
  "ltd stirling displacer size"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 9,
 "url": "https://xemstudio.com/objects/ltd-coffee-cup-engine-kit/",
 "sheet_txt": "https://xemstudio.com/objects/ltd-coffee-cup-engine-kit/sheet.txt",
 "sheet": {
  "basis": "Senft / Kolin LTD gamma proportions: displacer diameter ≫ stroke (D/stroke ≈ 15–25), displacer swept volume 10–20× the power piston swept volume, thin chamber (height ≈ 1.5 × displacer thickness)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "An LTD runs on a cup of coffee or a warm hand: a wide thin chamber between two conductive plates (aluminium, 1–3 mm), a foam displacer filling it with a 2 mm gap, a tiny power piston (syringe) and a crank with the displacer 90° ahead. Everything is about low friction and large area: Ø100 chamber, 16 mm tall, Ø96 × 8 foam displacer, 6 mm displacer stroke, 10 mL syringe at 4–6 mm stroke.",
   "Plates: the printed bottom plate is a drilling template; the real plate must be metal (aluminium 2 mm) for heat to get in. The top plate can be printed (it is the cold side: PETG, with the syringe socket and rod guide) or metal with the printed boss glued on. Chamber ring: printed, 10 mm wall, sealed to the plates with silicone or a 1.5 mm O-ring in the Ø100 groove (a static seal between ring and plates; nothing moving touches it, the piston and rod run on clearance fits).",
   "Numbers: 10 mL syringe (Ø14.5) at 5 mm stroke = 0.83 mL; displacer Ø96 × 6 mm stroke = 43 mL → ratio 52 (high, fine for ΔT 20 K). Flywheel Ø100 CD or the crank kit. Runs at 1–3 Hz on 15–20 °C ΔT.",
   "LES: the warm-hand demonstrator that opens the thermodynamics video."
  ],
  "table": {
   "columns": [
    "part",
    "Ø100 kit",
    "Ø150 kit"
   ],
   "rows": [
    [
     "chamber bore × height",
     "100 × 16",
     "150 × 16"
    ],
    [
     "displacer",
     "Ø96 × 8 foam, 6 stroke",
     "Ø146 × 8, 6 stroke"
    ],
    [
     "plates",
     "Ø120 × 2 Al",
     "Ø170 × 2 Al"
    ],
    [
     "power piston",
     "10 mL syringe, 5 stroke",
     "20 mL syringe, 5 stroke"
    ],
    [
     "displacer : piston volume",
     "~50",
     "~60"
    ],
    [
     "ΔT to run",
     "15–20 K",
     "10–15 K"
    ]
   ]
  }
 },
 "sheet_text": "LTD (low-temperature differential, coffee-cup) Stirling kit: plates, chamber ring, displacer, top plate with syringe cylinder — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/ltd-coffee-cup-engine-kit/  (CC BY 4.0)\nBasis: Senft / Kolin LTD gamma proportions: displacer diameter ≫ stroke (D/stroke ≈ 15–25), displacer swept volume 10–20× the power piston swept volume, thin chamber (height ≈ 1.5 × displacer thickness)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- An LTD runs on a cup of coffee or a warm hand: a wide thin chamber between two conductive plates (aluminium, 1–3 mm), a foam displacer filling it with a 2 mm gap, a tiny power piston (syringe) and a crank with the displacer 90° ahead. Everything is about low friction and large area: Ø100 chamber, 16 mm tall, Ø96 × 8 foam displacer, 6 mm displacer stroke, 10 mL syringe at 4–6 mm stroke.\n- Plates: the printed bottom plate is a drilling template; the real plate must be metal (aluminium 2 mm) for heat to get in. The top plate can be printed (it is the cold side: PETG, with the syringe socket and rod guide) or metal with the printed boss glued on. Chamber ring: printed, 10 mm wall, sealed to the plates with silicone or a 1.5 mm O-ring in the Ø100 groove (a static seal between ring and plates; nothing moving touches it, the piston and rod run on clearance fits).\n- Numbers: 10 mL syringe (Ø14.5) at 5 mm stroke = 0.83 mL; displacer Ø96 × 6 mm stroke = 43 mL → ratio 52 (high, fine for ΔT 20 K). Flywheel Ø100 CD or the crank kit. Runs at 1–3 Hz on 15–20 °C ΔT.\n- LES: the warm-hand demonstrator that opens the thermodynamics video.\n\npart  Ø100 kit  Ø150 kit\nchamber bore × height  100 × 16  150 × 16\ndisplacer  Ø96 × 8 foam, 6 stroke  Ø146 × 8, 6 stroke\nplates  Ø120 × 2 Al  Ø170 × 2 Al\npower piston  10 mL syringe, 5 stroke  20 mL syringe, 5 stroke\ndisplacer : piston volume  ~50  ~60\nΔT to run  15–20 K  10–15 K\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, 9 parts): https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/index.json\nAPI: https://xemstudio.com/api/geometry?object=ltd-coffee-cup-engine-kit\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": [
  "plastic-syringes",
  "crank-conrod-flywheel-kit",
  "cd-dvd-and-drive-platters",
  "brass-tube-ks",
  "balloons-and-diaphragms",
  "stirling-configurations-guide"
 ],
 "fits": [
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "crank-conrod-flywheel-kit",
     "why": "crank disc, con-rods, flywheel"
    },
    {
     "slug": "syringe-pistons",
     "why": "power piston in the top plate's syringe"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "can-engine-printed-kit",
     "why": "can engine"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "plastic-syringes",
     "why": "barrel"
    },
    {
     "slug": "ball-bearings-metric",
     "why": "623 in the stands"
    }
   ]
  }
 ],
 "faq": [
  {
   "q": "What size displacer for a coffee cup Stirling engine?",
   "a": "Ø96 × 8 mm foam in a Ø100 × 16 chamber with a 6 mm stroke; the displacer swept volume should be 20–60× the power piston's."
  },
  {
   "q": "Why does an LTD have such a big displacer?",
   "a": "With only 15–20 K of temperature difference the gas changes pressure very little, so you need a lot of gas shuttled per cycle and almost no friction: big area, small stroke, tiny piston."
  },
  {
   "q": "Can the plates be 3D printed?",
   "a": "The cold (top) plate yes; the hot plate must be metal (2 mm aluminium) or the heat never gets into the gas. Use the printed bottom plate as the drilling template."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "ltd-100-bottom-plate-template",
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    "step",
    "stl"
   ],
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   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-100-bottom-plate-template.step",
   "stl": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-100-bottom-plate-template.stl",
   "note": "bottom plate template Ø120 × 3 (cut aluminium to this; the printed one is for layout), 6 × M3"
  },
  {
   "file": "ltd-100-chamber-ring-h16",
   "formats": [
    "step",
    "stl"
   ],
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   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-100-chamber-ring-h16.step",
   "stl": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-100-chamber-ring-h16.stl",
   "note": "chamber ring Ø100 bore × 16 tall, 10 mm wall, 6 × M3; the displacer runs inside"
  },
  {
   "file": "ltd-100-displacer-foam-template",
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   ],
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   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-100-displacer-foam-template.step",
   "stl": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-100-displacer-foam-template.stl",
   "note": "displacer template Ø96 × 8 (cut from foam; 2 mm radial gap)"
  },
  {
   "file": "ltd-100-top-plate-syringe",
   "formats": [
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   "stl": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-100-top-plate-syringe.stl",
   "note": "top plate Ø120 with 3/32 in rod guide boss on centre and a 10 mL syringe socket as the power cylinder"
  },
  {
   "file": "ltd-150-bottom-plate-template",
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   "stl": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-150-bottom-plate-template.stl",
   "note": "bottom plate template Ø170 × 3 (cut aluminium to this; the printed one is for layout), 6 × M3"
  },
  {
   "file": "ltd-150-chamber-ring-h16",
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    "step",
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   "stl": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-150-chamber-ring-h16.stl",
   "note": "chamber ring Ø150 bore × 16 tall, 10 mm wall, 6 × M3; the displacer runs inside"
  },
  {
   "file": "ltd-150-displacer-foam-template",
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   "stl": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-150-displacer-foam-template.stl",
   "note": "displacer template Ø146 × 8 (cut from foam; 2 mm radial gap)"
  },
  {
   "file": "ltd-150-top-plate-syringe",
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    "stl"
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   "stl": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-150-top-plate-syringe.stl",
   "note": "top plate Ø170 with 3/32 in rod guide boss on centre and a 10 mL syringe socket as the power cylinder"
  },
  {
   "file": "ltd-crank-stand-pair",
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    "step",
    "stl"
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   "price_usd": 0,
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   "step": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-crank-stand-pair.step",
   "stl": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-crank-stand-pair.stl",
   "note": "crank stand 45 mm tall with a 623 pocket (print two)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/ltd-coffee-cup-engine-kit/index.md"
}