{
 "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": "free-piston-mover-2in",
 "name": "Free-piston mover for a 2 in honed spool: piston and alternator magnets in one, Ø48.00 × 130",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Tri-clamp engine parts",
 "year": null,
 "question": "How do I make a free piston that is also the alternator's moving magnet?",
 "tags": [
  "free piston",
  "piston",
  "mover",
  "linear alternator",
  "magnet",
  "tri-clamp",
  "long earth society",
  "thermoacoustic"
 ],
 "aliases": [
  "free piston mover magnets",
  "moving magnet piston 2 inch",
  "linear alternator mover tri clamp"
 ],
 "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/free-piston-mover-2in/",
 "sheet_txt": "https://xemstudio.com/objects/free-piston-mover-2in/sheet.txt",
 "sheet": {
  "basis": "Ø48.00 to the honed spool; magnet rows and pitch from the alternator design in tools/gen_ta_power.py",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The piston and the alternator's moving part are one: a 12-sided core carries 4 rows of 12 block magnets (30 × 10 × 4, magnetised through 4), rows alternately N and S outward at 32 mm pitch, and a sleeve Ø48.00 / Ø47 slides over them and runs in the honed bore. The core is the magnets' return path, so it has to carry magnetic flux; what it and the sleeve are made of is the builder's choice within that.",
   "The crown is closed; an M4 threaded rod screws into it from inside the Ø20 bore and carries the two flexure stacks below. Moving mass with the magnets, rod and hub parts: about 1.39 kg (core and sleeve counted at 7.8 g/cm³, magnets at 7.5).",
   "Design stroke ±8 mm: the 30 mm magnet rows stay fully over their 14 mm coils that far.",
   "Fits: sleeve OD is the clearance seal in the honed bore (run); the sleeve's bore slides over the core's flanges (press); the magnets sit on the flats (bonded, designed)."
  ],
  "table": {
   "columns": [
    "feature",
    "value"
   ],
   "rows": [
    [
     "length",
     "130"
    ],
    [
     "sleeve",
     "Ø48.00 / Ø47"
    ],
    [
     "magnets",
     "4 × 12 blocks 30 × 10 × 4"
    ],
    [
     "row pitch",
     "32"
    ],
    [
     "moving mass",
     "≈ 1.39 kg"
    ],
    [
     "design stroke",
     "±8"
    ]
   ]
  }
 },
 "sheet_text": "Free-piston mover for a 2 in honed spool: piston and alternator magnets in one, Ø48.00 × 130 — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/free-piston-mover-2in/  (CC BY 4.0)\nBasis: Ø48.00 to the honed spool; magnet rows and pitch from the alternator design in tools/gen_ta_power.py\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The piston and the alternator's moving part are one: a 12-sided core carries 4 rows of 12 block magnets (30 × 10 × 4, magnetised through 4), rows alternately N and S outward at 32 mm pitch, and a sleeve Ø48.00 / Ø47 slides over them and runs in the honed bore. The core is the magnets' return path, so it has to carry magnetic flux; what it and the sleeve are made of is the builder's choice within that.\n- The crown is closed; an M4 threaded rod screws into it from inside the Ø20 bore and carries the two flexure stacks below. Moving mass with the magnets, rod and hub parts: about 1.39 kg (core and sleeve counted at 7.8 g/cm³, magnets at 7.5).\n- Design stroke ±8 mm: the 30 mm magnet rows stay fully over their 14 mm coils that far.\n- Fits: sleeve OD is the clearance seal in the honed bore (run); the sleeve's bore slides over the core's flanges (press); the magnets sit on the flats (bonded, designed).\n\nfeature  value\nlength  130\nsleeve  Ø48.00 / Ø47\nmagnets  4 × 12 blocks 30 × 10 × 4\nrow pitch  32\nmoving mass  ≈ 1.39 kg\ndesign stroke  ±8\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Appl. Phys. Lett. (S. Backhaus, E. Tward, M. Petach): Traveling-wave thermoacoustic electric generator, APL 85, 1085 (2004): a thermoacoustic-Stirling engine driving linear alternators, 18 % heat to electricity — web — journal article; cited [verify license at link] — https://doi.org/10.1063/1.1781739\n- Applied Energy (Z. Wu, G. Yu, L. Zhang, W. Dai, E. Luo): Development of a 3 kW double-acting thermoacoustic Stirling electric generator, 136, 866-872 (2014): three engines and three linear alternators in a loop, 5 MPa helium, 86 Hz, 1.57 kW electric, 16.8 % — web — journal article; cited [verify license at link] — https://doi.org/10.1016/j.apenergy.2014.04.105\n- Xem Studio: tools/gen_ta_power.py: the network model and every dimension on this page — code — CC BY 4.0 — https://xemstudio.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/free-piston-mover-2in/index.json\nAPI: https://xemstudio.com/api/geometry?object=free-piston-mover-2in\n",
 "sources": [
  {
   "publisher": "Appl. Phys. Lett. (S. Backhaus, E. Tward, M. Petach)",
   "title": "Traveling-wave thermoacoustic electric generator, APL 85, 1085 (2004): a thermoacoustic-Stirling engine driving linear alternators, 18 % heat to electricity",
   "url": "https://doi.org/10.1063/1.1781739",
   "formats": [
    "web"
   ],
   "license": "journal article; cited",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "Applied Energy (Z. Wu, G. Yu, L. Zhang, W. Dai, E. Luo)",
   "title": "Development of a 3 kW double-acting thermoacoustic Stirling electric generator, 136, 866-872 (2014): three engines and three linear alternators in a loop, 5 MPa helium, 86 Hz, 1.57 kW electric, 16.8 %",
   "url": "https://doi.org/10.1016/j.apenergy.2014.04.105",
   "formats": [
    "web"
   ],
   "license": "journal article; cited",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "Xem Studio",
   "title": "tools/gen_ta_power.py: the network model and every dimension on this page",
   "url": "https://xemstudio.com/",
   "formats": [
    "code"
   ],
   "license": "CC BY 4.0",
   "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": [
  "tri-clamp-honed-cylinder-spool",
  "canned-linear-alternator-stator-2in",
  "neodymium-block-magnets",
  "tri-clamp-flexure-carrier",
  "list-ta-ring-3x2in"
 ],
 "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": "sleeve outside",
   "exact": "Ø48.00 × 130",
   "mates": "honed spool bore Ø48.00: clearance seal",
   "fit": "run",
   "files": "mover-sleeve-"
  },
  {
   "feature": "sleeve bore",
   "exact": "Ø47.00",
   "mates": "mover core end flanges Ø47.00",
   "fit": "press",
   "files": "all"
  },
  {
   "feature": "flats",
   "exact": "12 × 10 wide on r 18.66, 4 rows of 30 at 32 pitch",
   "mates": "block magnets 30 × 10 × 4 (bonded)",
   "fit": "designed",
   "files": "mover-core-"
  },
  {
   "feature": "crown hole",
   "exact": "Ø3.3 × 6 (M4 tap drill) from the Ø20 bore",
   "mates": "M4 threaded rod",
   "fit": "designed",
   "files": "mover-core-"
  },
  {
   "feature": "core bore",
   "exact": "Ø20 from the bottom face to the crown",
   "mates": "M4 rod (no contact)",
   "fit": "designed",
   "files": "mover-core-"
  }
 ],
 "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": "Where is the rod?",
   "a": "Inside: it screws into the crown from the bore and leaves through the bottom to the flexures. Nothing crosses the pressure wall."
  },
  {
   "q": "Why a sleeve?",
   "a": "The magnets cannot be the running surface; the sleeve is, finished to the clearance-seal fit."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "mover-core-2in-130",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/free-piston-mover-2in/mover-core-2in-130.step",
   "stl": "https://xemstudio.com/files/hardware/free-piston-mover-2in/mover-core-2in-130.stl",
   "note": "mover core, 130 long: 12-sided body (flats r 18.66) between Ø47 × 2 end flanges, Ø20 bore from the bottom to an 8 mm crown, M4 tap drill Ø3.3 × 6 in the crown"
  },
  {
   "file": "mover-sleeve-48x130",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/free-piston-mover-2in/mover-sleeve-48x130.step",
   "stl": "https://xemstudio.com/files/hardware/free-piston-mover-2in/mover-sleeve-48x130.stl",
   "note": "mover sleeve Ø48.00 / Ø47 × 130: the running surface"
  }
 ],
 "markdown": "https://xemstudio.com/objects/free-piston-mover-2in/index.md"
}