{
 "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-bottom-plate",
 "name": "LTD Stirling bottom plate, Ø120 and Ø170",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Can & LTD engines",
 "year": null,
 "question": "What are the dimensions of the bottom (hot) plate of a coffee-cup Stirling engine?",
 "tags": [
  "ltd",
  "hot plate",
  "bottom plate",
  "coffee cup",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "ltd stirling bottom plate",
  "coffee cup stirling hot plate size",
  "ltd plate 120 mm",
  "low temperature stirling base plate"
 ],
 "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-bottom-plate/",
 "sheet_txt": "https://xemstudio.com/objects/ltd-bottom-plate/sheet.txt",
 "sheet": {
  "basis": "Same outline and M3 hole circle as the LTD top plate and chamber ring; M3 clearance Ø3.4 (ISO 273)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The hot plate of the LTD engine: the cup or the hand warms it and the heat goes through it into the air in the chamber.",
   "Ø120 × 3 for the 100 chamber, Ø170 × 3 for the 150, with 6 × Ø3.4 on a Ø112 / Ø162 circle (at 30°, 90°, …) matching the chamber ring and top plate; an M3 × 12 from below goes into each tapped ring hole."
  ],
  "table": {
   "columns": [
    "file",
    "plate",
    "holes",
    "screw circle",
    "centre mark"
   ],
   "rows": [
    [
     "ltd-100-bottom-plate",
     "Ø120 × 3",
     "6 × Ø3.4",
     112,
     3.2
    ],
    [
     "ltd-150-bottom-plate",
     "Ø170 × 3",
     "6 × Ø3.4",
     162,
     3.2
    ]
   ]
  }
 },
 "sheet_text": "LTD Stirling bottom plate, Ø120 and Ø170 — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/ltd-bottom-plate/  (CC BY 4.0)\nBasis: Same outline and M3 hole circle as the LTD top plate and chamber ring; M3 clearance Ø3.4 (ISO 273)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The hot plate of the LTD engine: the cup or the hand warms it and the heat goes through it into the air in the chamber.\n- Ø120 × 3 for the 100 chamber, Ø170 × 3 for the 150, with 6 × Ø3.4 on a Ø112 / Ø162 circle (at 30°, 90°, …) matching the chamber ring and top plate; an M3 × 12 from below goes into each tapped ring hole.\n\nfile  plate  holes  screw circle  centre mark\nltd-100-bottom-plate  Ø120 × 3  6 × Ø3.4  112  3.2\nltd-150-bottom-plate  Ø170 × 3  6 × Ø3.4  162  3.2\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-bottom-plate/index.json\nAPI: https://xemstudio.com/api/geometry?object=ltd-bottom-plate\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-displacer",
  "list-ltd-coffee-cup"
 ],
 "fits": [
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "ltd-chamber-ring",
     "why": "6 × M3 on the Ø112 / Ø162 circle, ring between the plates"
    },
    {
     "slug": "ltd-top-plate",
     "why": "same outline and hole circle on the other face of the ring"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "socket-head-cap-screws-metric",
     "why": "6 × M3 through plate, ring and plate"
    }
   ]
  }
 ],
 "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": "plate screw holes",
   "exact": "Ø3.4",
   "mates": "M3 screw clearance (ISO 273)",
   "fit": "designed",
   "files": "ltd-100-bottom"
  },
  {
   "feature": "plate screw holes",
   "exact": "Ø3.4",
   "mates": "M3 screw clearance (ISO 273)",
   "fit": "designed",
   "files": "ltd-150-bottom"
  }
 ],
 "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 big is the bottom plate of a 100 mm LTD Stirling?",
   "a": "Ø120 × 3 with six Ø3.4 holes on a Ø112 circle."
  },
  {
   "q": "Does the bottom plate have the same holes as the top plate?",
   "a": "Yes: 6 × Ø3.4 on the same Ø112 / Ø162 circle as the top plate; the chamber ring between them has the same holes tapped M3."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "ltd-100-bottom-plate",
   "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-bottom-plate.step",
   "stl": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-100-bottom-plate.stl",
   "note": "bottom (hot) plate Ø120 × 3, 6 × Ø3.4 (M3 clearance) on a Ø112 circle at 30° + 60° steps"
  },
  {
   "file": "ltd-150-bottom-plate",
   "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-bottom-plate.step",
   "stl": "https://xemstudio.com/files/hardware/ltd-coffee-cup-engine-kit/ltd-150-bottom-plate.stl",
   "note": "bottom (hot) plate Ø170 × 3, 6 × Ø3.4 (M3 clearance) on a Ø162 circle at 30° + 60° steps"
  }
 ],
 "markdown": "https://xemstudio.com/objects/ltd-bottom-plate/index.md"
}