{
 "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": "linear-alternator-module-tuning-2in",
 "name": "Linear alternator module tuning parts: add-on mass discs, the soft 0.5 mm leaf and its rim shim",
 "kind": "hardware",
 "category": "Electronics",
 "group": "Generators & alternators",
 "year": null,
 "question": "How do I retune the clamp-in linear alternator module to another engine's frequency?",
 "tags": [
  "tuning",
  "mass",
  "flexure",
  "linear alternator",
  "resonance",
  "tri-clamp",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "linear alternator tuning mass",
  "free piston resonance tuning",
  "soft flexure leaf",
  "change natural frequency free piston"
 ],
 "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/linear-alternator-module-tuning-2in/",
 "sheet_txt": "https://xemstudio.com/objects/linear-alternator-module-tuning-2in/sheet.txt",
 "sheet": {
  "basis": "Natural frequency f = √(k/m) / 2π of the mover on its leaves and bounce gas spring (k_b = γ p A² / V_b, adiabatic); masses from the CAD at 7.9 g/cm³ (assumed); leaf stiffness from the generator's frame model (E 200 GPa assumed)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "What moves the frequency, largest first: the charge behind the piston, the bounce volume, the leaves, the mass. The discs are the fine trim: four of them lower the frequency by about 5 %, because the mover already carries 865 g of magnets and return path.",
   "Coarse tuning without new parts: a stock 2 in spool between face B and the cap (one more gasket and clamp) softens the bounce gas spring. With a 3 in spool: 295 cm³, 17.5 / 28.3 Hz (air 1 bar / helium 10 bar, standard leaves); with a 6 in spool: 430 cm³, 17.1 / 25.1 Hz.",
   "Mass down, frequency down: each disc adds 24.1 g. Discs stack on the crown inside the cup (Ø26 bore on the hub boss) and are held by three M3 screws into the crown's tapped holes: 1 disc M3 × 8, 2 discs M3 × 12, 3 discs M3 × 16, 4 discs M3 × 20 (always 4 mm of thread in the crown; the heads stay inside the cup).",
   "Spring down: the soft leaf is the 0.8 leaf's outline at 0.5 thick, 1135 N/m against 4426 N/m axially (stiffness goes with thickness cubed). Fit both leaves soft, each between two 0.6 half gaskets (0.6 + 0.5 + 0.6 = 1.7, the joint). One leaf per joint is the rule: two leaves in one joint would rub on each other, and a joint holds only 1.7. In the open-frame module each soft leaf sits on a 0.3 rim shim in the 0.8 seat.",
   "Spring up: charge. With face B closed the bounce gas is the stiffest spring in the module: 3.0 kN/m at 1 bar air, 29.2 kN/m at 10 bar air, 34.8 kN/m at 10 bar helium (157 cm³ behind the piston). A stock 2 in spool between face B and the cap adds volume and softens it (k_b falls in proportion).",
   "The table is the module alone. On an engine the working gas on face A adds its own stiffness (and the engine's power): the module's frequency on the engine is the engine's, and it is measured, not set.",
   "Open-frame module: no bounce space, so the leaves and the mass are the whole module spring: 15.8 Hz with the 0.8 leaves and no disc, 15.0 Hz with four discs, 8.0 Hz on the soft leaves (moving mass 899 g, its tube rod is longer). The engine's own gas on face A adds to it; the datasheet lists that for engine volumes from 50 to 400 cm³."
  ],
  "table": {
   "columns": [
    "discs",
    "mass_g",
    "std_open_Hz",
    "std_air1_Hz",
    "std_air10_Hz",
    "std_He10_Hz",
    "soft_open_Hz",
    "soft_air1_Hz",
    "soft_He10_Hz"
   ],
   "rows": [
    [
     0,
     865,
     16.1,
     18.6,
     33.4,
     35.8,
     8.2,
     12.4,
     33
    ],
    [
     1,
     889,
     15.9,
     18.3,
     32.9,
     35.3,
     8.1,
     12.2,
     32.6
    ],
    [
     2,
     913,
     15.7,
     18.1,
     32.5,
     34.8,
     7.9,
     12.1,
     32.1
    ],
    [
     3,
     937,
     15.5,
     17.9,
     32.1,
     34.4,
     7.8,
     11.9,
     31.7
    ],
    [
     4,
     961,
     15.3,
     17.6,
     31.7,
     33.9,
     7.7,
     11.8,
     31.3
    ]
   ]
  }
 },
 "sheet_text": "Linear alternator module tuning parts: add-on mass discs, the soft 0.5 mm leaf and its rim shim — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/linear-alternator-module-tuning-2in/  (CC BY 4.0)\nBasis: Natural frequency f = √(k/m) / 2π of the mover on its leaves and bounce gas spring (k_b = γ p A² / V_b, adiabatic); masses from the CAD at 7.9 g/cm³ (assumed); leaf stiffness from the generator's frame model (E 200 GPa assumed)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- What moves the frequency, largest first: the charge behind the piston, the bounce volume, the leaves, the mass. The discs are the fine trim: four of them lower the frequency by about 5 %, because the mover already carries 865 g of magnets and return path.\n- Coarse tuning without new parts: a stock 2 in spool between face B and the cap (one more gasket and clamp) softens the bounce gas spring. With a 3 in spool: 295 cm³, 17.5 / 28.3 Hz (air 1 bar / helium 10 bar, standard leaves); with a 6 in spool: 430 cm³, 17.1 / 25.1 Hz.\n- Mass down, frequency down: each disc adds 24.1 g. Discs stack on the crown inside the cup (Ø26 bore on the hub boss) and are held by three M3 screws into the crown's tapped holes: 1 disc M3 × 8, 2 discs M3 × 12, 3 discs M3 × 16, 4 discs M3 × 20 (always 4 mm of thread in the crown; the heads stay inside the cup).\n- Spring down: the soft leaf is the 0.8 leaf's outline at 0.5 thick, 1135 N/m against 4426 N/m axially (stiffness goes with thickness cubed). Fit both leaves soft, each between two 0.6 half gaskets (0.6 + 0.5 + 0.6 = 1.7, the joint). One leaf per joint is the rule: two leaves in one joint would rub on each other, and a joint holds only 1.7. In the open-frame module each soft leaf sits on a 0.3 rim shim in the 0.8 seat.\n- Spring up: charge. With face B closed the bounce gas is the stiffest spring in the module: 3.0 kN/m at 1 bar air, 29.2 kN/m at 10 bar air, 34.8 kN/m at 10 bar helium (157 cm³ behind the piston). A stock 2 in spool between face B and the cap adds volume and softens it (k_b falls in proportion).\n- The table is the module alone. On an engine the working gas on face A adds its own stiffness (and the engine's power): the module's frequency on the engine is the engine's, and it is measured, not set.\n- Open-frame module: no bounce space, so the leaves and the mass are the whole module spring: 15.8 Hz with the 0.8 leaves and no disc, 15.0 Hz with four discs, 8.0 Hz on the soft leaves (moving mass 899 g, its tube rod is longer). The engine's own gas on face A adds to it; the datasheet lists that for engine volumes from 50 to 400 cm³.\n\ndiscs  mass_g  std_open_Hz  std_air1_Hz  std_air10_Hz  std_He10_Hz  soft_open_Hz  soft_air1_Hz  soft_He10_Hz\n0  865  16.1  18.6  33.4  35.8  8.2  12.4  33.0\n1  889  15.9  18.3  32.9  35.3  8.1  12.2  32.6\n2  913  15.7  18.1  32.5  34.8  7.9  12.1  32.1\n3  937  15.5  17.9  32.1  34.4  7.8  11.9  31.7\n4  961  15.3  17.6  31.7  33.9  7.7  11.8  31.3\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Xem Studio: tools/gen_la_module.py: the module's geometry, masses, bounce volume, natural frequencies and every number on these pages — code — CC BY 4.0 — https://xemstudio.com/\n- Xem Studio: tools/gen_fpse_gen.py: the free-piston generator whose stator, magnets, leaves and collars this module reuses; its leaf frame model and magnetic-circuit estimate — 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, 3 parts): https://xemstudio.com/files/hardware/linear-alternator-module-tuning-2in/index.json\nAPI: https://xemstudio.com/api/geometry?object=linear-alternator-module-tuning-2in\n",
 "sources": [
  {
   "publisher": "Xem Studio",
   "title": "tools/gen_la_module.py: the module's geometry, masses, bounce volume, natural frequencies and every number on these pages",
   "url": "https://xemstudio.com/",
   "formats": [
    "code"
   ],
   "license": "CC BY 4.0",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Xem Studio",
   "title": "tools/gen_fpse_gen.py: the free-piston generator whose stator, magnets, leaves and collars this module reuses; its leaf frame model and magnetic-circuit estimate",
   "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": [
  "linear-alternator-module-mover-2in",
  "linear-alternator-module-open-frame-2in",
  "tri-clamp-flexure-leaf",
  "tri-clamp-leaf-half-gasket",
  "linear-alternator-module-2in-datasheet",
  "list-linear-alternator-module-2in-closed",
  "list-linear-alternator-module-2in-open"
 ],
 "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": "bore",
   "exact": "Ø26",
   "mates": "piston cup hub boss",
   "fit": "slide",
   "files": "la-mass-disc"
  },
  {
   "feature": "OD",
   "exact": "Ø41",
   "mates": "piston cup skirt bore Ø42 (0.5 radial gap, no contact)",
   "fit": "designed",
   "files": "la-mass-disc"
  },
  {
   "feature": "holes",
   "exact": "3 × Ø3.4 on r 17",
   "mates": "M3 clearance (ISO 273 medium)",
   "fit": "designed",
   "files": "la-mass-disc"
  },
  {
   "feature": "rim",
   "exact": "Ø64 × 0.5, clamped from Ø47.5 out",
   "mates": "two 0.6 half gaskets in the joint; centred on the Ø64 flange rims by the clamp",
   "fit": "clamp",
   "files": "leaf-2in-piston-t0.5"
  },
  {
   "feature": "hub bore",
   "exact": "Ø18",
   "mates": "tube rod, hub clamped by two collars",
   "fit": "slide",
   "files": "leaf-2in-piston-t0.5"
  },
  {
   "feature": "arms",
   "exact": "three spiral arms inside Ø47.5",
   "mates": "free (no contact)",
   "fit": "designed",
   "files": "leaf-2in-piston-t0.5"
  },
  {
   "feature": "rim",
   "exact": "Ø64 × 0.5 on a 0.3 shim (open frame)",
   "mates": "open frame's Ø64 × 0.8 leaf seat under a clamp ring",
   "fit": "clamp",
   "files": "leaf-2in-piston-t0.5"
  },
  {
   "feature": "OD",
   "exact": "Ø64",
   "mates": "open frame's Ø64 leaf seat (under a 0.5 leaf's rim)",
   "fit": "clamp",
   "files": "la-rim-shim"
  },
  {
   "feature": "faces",
   "exact": "0.3 thick, Ø47.5–Ø64",
   "mates": "seat floor and the 0.5 leaf's rim",
   "fit": "clamp",
   "files": "la-rim-shim"
  }
 ],
 "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": "Which way does each change go?",
   "a": "Discs lower the frequency; soft leaves lower it (most at 1 bar, little at 10 bar where the bounce gas dominates); more charge or less bounce volume raise it."
  },
  {
   "q": "Is the soft leaf strong enough?",
   "a": "Its bending stress is 114 MPa at ±6 mm against 177 MPa for the 0.8 leaf: lower, because it is thinner."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "la-mass-disc-41x26x4",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/linear-alternator-module-tuning-2in/la-mass-disc-41x26x4.step",
   "stl": "https://xemstudio.com/files/hardware/linear-alternator-module-tuning-2in/la-mass-disc-41x26x4.stl",
   "note": "add-on mass disc Ø41 / Ø26 × 4, 3 × Ø3.4 on r 17: up to 4 stack on the cup's crown inside its skirt, 24.1 g each at 7.9 g/cm³"
  },
  {
   "file": "leaf-2in-piston-t0.5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/linear-alternator-module-tuning-2in/leaf-2in-piston-t0.5.step",
   "stl": "https://xemstudio.com/files/hardware/linear-alternator-module-tuning-2in/leaf-2in-piston-t0.5.stl",
   "note": "soft leaf: the 0.8 piston leaf's outline (Ø64 rim, Ø18 hub bore, 3 arms 4 wide sweeping 330°) at 0.5 thick; clamped between two 0.6 half gaskets (closed module) or on a 0.3 rim shim in the open frame's 0.8 seat"
  },
  {
   "file": "la-rim-shim-64x0.3",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/linear-alternator-module-tuning-2in/la-rim-shim-64x0.3.step",
   "stl": "https://xemstudio.com/files/hardware/linear-alternator-module-tuning-2in/la-rim-shim-64x0.3.stl",
   "note": "rim shim Ø64 / Ø47.5 × 0.3: under a 0.5 soft leaf's rim in the open frame's Ø64 × 0.8 leaf seat, so the clamp ring clamps it as it clamps a 0.8 leaf"
  }
 ],
 "markdown": "https://xemstudio.com/objects/linear-alternator-module-tuning-2in/index.md"
}