{
 "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": "fpse-displacer-rod",
 "name": "Free-piston displacer rod, plug and stinger: Ø12 rod through the power piston, Ø3 stinger to the gas spring",
 "kind": "hardware",
 "category": "Hardware",
 "group": "Stirling & thermoacoustic",
 "year": null,
 "question": "How does the displacer of a Beale free-piston Stirling get its drive and its spring?",
 "tags": [
  "displacer rod",
  "stinger",
  "free piston",
  "tri-clamp",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "displacer rod through piston",
  "beale free piston rod",
  "stinger rod"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 3,
 "url": "https://xemstudio.com/objects/fpse-displacer-rod/",
 "sheet_txt": "https://xemstudio.com/objects/fpse-displacer-rod/sheet.txt",
 "sheet": {
  "basis": "Beale free-piston layout (rod area drive), Redlich & Berchowitz linear dynamics; stinger stiffness from Euler beam relations",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The rod's area (Ø12) is the displacer's drive: the working gas pushes on it from below and the bounce space from above, and that difference, swinging with the piston, pushes the displacer ahead of the piston (the Beale free-piston principle).",
   "It runs up through leaf B's hub (clamped there by the cap's boss and a collar) and the piston's Ø12 hub bore, a running fit 76 mm long that is also the seal between working and bounce space, to the plug at its top.",
   "The Ø3 stinger joins the plug to the gas-spring piston: stiff along its length, soft sideways (87 mm free), so the gas spring's own cylinder does not fight the rod's alignment through the piston."
  ],
  "table": {
   "columns": [
    "part",
    "size"
   ],
   "rows": [
    [
     "rod",
     "Ø12 / Ø10 × 260.45"
    ],
    [
     "plug",
     "Ø10 × 8 spigot, Ø12 × 8 head"
    ],
    [
     "stinger",
     "Ø3 × 87.05"
    ]
   ]
  }
 },
 "sheet_text": "Free-piston displacer rod, plug and stinger: Ø12 rod through the power piston, Ø3 stinger to the gas spring — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/fpse-displacer-rod/  (CC BY 4.0)\nBasis: Beale free-piston layout (rod area drive), Redlich & Berchowitz linear dynamics; stinger stiffness from Euler beam relations\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The rod's area (Ø12) is the displacer's drive: the working gas pushes on it from below and the bounce space from above, and that difference, swinging with the piston, pushes the displacer ahead of the piston (the Beale free-piston principle).\n- It runs up through leaf B's hub (clamped there by the cap's boss and a collar) and the piston's Ø12 hub bore, a running fit 76 mm long that is also the seal between working and bounce space, to the plug at its top.\n- The Ø3 stinger joins the plug to the gas-spring piston: stiff along its length, soft sideways (87 mm free), so the gas spring's own cylinder does not fight the rod's alignment through the piston.\n\npart  size\nrod  Ø12 / Ø10 × 260.45\nplug  Ø10 × 8 spigot, Ø12 × 8 head\nstinger  Ø3 × 87.05\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Proc. IMechE Part A: Redlich & Berchowitz (1985), Linear dynamics of free-piston Stirling engines — PDF — journal; method cited [verify license at link] — https://journals.sagepub.com/doi/pdf/10.1243/PIME_PROC_1985_199_025_02\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, 3 parts): https://xemstudio.com/files/hardware/fpse-displacer-rod/index.json\nAPI: https://xemstudio.com/api/geometry?object=fpse-displacer-rod\n",
 "sources": [
  {
   "publisher": "Proc. IMechE Part A",
   "title": "Redlich & Berchowitz (1985), Linear dynamics of free-piston Stirling engines",
   "url": "https://journals.sagepub.com/doi/pdf/10.1243/PIME_PROC_1985_199_025_02",
   "formats": [
    "PDF"
   ],
   "license": "journal; method cited",
   "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": [
  "fpse-displacer",
  "fpse-displacer-gas-spring",
  "fpse-power-piston",
  "list-fpse-generator-2in"
 ],
 "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": "rod OD",
   "exact": "Ø12",
   "mates": "piston hub bore Ø12 × 76 (seal and guide)",
   "fit": "run",
   "files": "fpse-displacer-rod"
  },
  {
   "feature": "rod OD",
   "exact": "Ø12",
   "mates": "leaf B's hub and the collar (M3 grub)",
   "fit": "slide",
   "files": "fpse-displacer-rod"
  },
  {
   "feature": "rod OD",
   "exact": "Ø12",
   "mates": "tube rod bore Ø14 (no contact)",
   "fit": "designed",
   "files": "fpse-displacer-rod"
  },
  {
   "feature": "rod bore",
   "exact": "Ø10",
   "mates": "plug spigot",
   "fit": "press",
   "files": "fpse-displacer-rod"
  },
  {
   "feature": "spigot",
   "exact": "Ø10 × 8",
   "mates": "rod bore",
   "fit": "press",
   "files": "fpse-rod-plug"
  },
  {
   "feature": "stinger socket",
   "exact": "Ø3 × 10",
   "mates": "stinger, held by an M3 grub",
   "fit": "slide",
   "files": "fpse-rod-plug"
  },
  {
   "feature": "grub hole",
   "exact": "Ø2.5",
   "mates": "M3 tap drill",
   "fit": "designed",
   "files": "fpse-rod-plug"
  },
  {
   "feature": "stinger",
   "exact": "Ø3",
   "mates": "gland bore Ø3 × 13 (seal)",
   "fit": "run",
   "files": "fpse-stinger"
  },
  {
   "feature": "stinger ends",
   "exact": "Ø3 × 10",
   "mates": "plug and gas-spring piston sockets",
   "fit": "slide",
   "files": "fpse-stinger"
  }
 ],
 "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 a stinger?",
   "a": "The rod is guided by the piston's bore and the gas-spring piston by its own cylinder, in a different spool; a slender link between them carries the spring force without forcing the two guides into line."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "fpse-displacer-rod-12x10",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/fpse-displacer-rod/fpse-displacer-rod-12x10.step",
   "stl": "https://xemstudio.com/files/hardware/fpse-displacer-rod/fpse-displacer-rod-12x10.stl",
   "note": "displacer rod: tube Ø12 / Ø10 × 260.45: through leaf B's hub and the piston's hub bore (running fit)"
  },
  {
   "file": "fpse-rod-plug-12",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/fpse-displacer-rod/fpse-rod-plug-12.step",
   "stl": "https://xemstudio.com/files/hardware/fpse-displacer-rod/fpse-rod-plug-12.stl",
   "note": "rod plug: Ø10 × 8 spigot into the rod's top, Ø12 × 8 head with a Ø3 × 10 stinger socket and an M3 tapped radial hole (Ø2.5)"
  },
  {
   "file": "fpse-stinger-3x87.05",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/fpse-displacer-rod/fpse-stinger-3x87.05.step",
   "stl": "https://xemstudio.com/files/hardware/fpse-displacer-rod/fpse-stinger-3x87.05.stl",
   "note": "stinger: Ø3 × 87.05: rod plug to the gas-spring piston, through the gland"
  }
 ],
 "markdown": "https://xemstudio.com/objects/fpse-displacer-rod/index.md"
}