{
 "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": "alpha-v-twin-frame",
 "name": "Alpha V-twin frame for two 10 mL syringes: frame, crank disc and con-rods sized so it actually runs",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "How do I hold two syringes and a crank together for an alpha Stirling engine?",
 "tags": [
  "alpha",
  "v-twin",
  "stirling",
  "syringe",
  "frame",
  "crank",
  "long earth society"
 ],
 "aliases": [
  "alpha stirling engine frame",
  "two syringe stirling engine",
  "v twin stirling syringe",
  "alpha stirling 3d print complete"
 ],
 "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/alpha-v-twin-frame/",
 "sheet_txt": "https://xemstudio.com/objects/alpha-v-twin-frame/sheet.txt",
 "sheet": {
  "basis": "Computed in the generator: crank throw 8, rod 60, 10 mL syringe piston (pin 8.6 above the skirt, 19 long), barrel 15.9 OD / 14.5 ID; checked over a full turn: skirt never closer than the barrel mouth, rod never within 0.5 mm of the barrel wall",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Phase: in a 90° V both con-rods ride ONE crank pin, and the 90° between the cylinders is the 90° alpha phase. (A two-pin disc with pins 90° apart is for parallel cylinders; under a 90° V it would give 0° or 180° and the engine would not run.)",
   "Geometry: crank axis at the origin; both barrel axes pass through it at ±45°. Barrel sockets start at R45 so the piston (bottom of skirt 43.4 mm from the axis at bottom dead centre) never leaves the barrel, and with a 60 mm rod the rod swings at most ±7.7°, keeping 0.8 mm from the barrel wall.",
   "Along the shaft (Y): 625 · boss · 625, 2 mm spacer, crank disc (6), 1 mm spacer, rod 1 (cylinder at +45°), 1 mm spacer, rod 2 (cylinder at −45°), Ø3 × 20 pin pressed 6 mm into the disc, 3 mm collar on its end. Flywheel (nut-weighted Ø100, b5) on the other end of the Ø5 × 80 shaft behind the boss.",
   "Barrels slide in from the crank side, tip outward, finger flange against the socket's inner face; M3 pinch screw. Pistons: syringe-piston-10ml (no plunger). Transfer: a short tube with a mesh plug between the tips (transfer tee).",
   "Foot: 2 × M5 at 50 mm into a 2020 rail; mount it at the rail's end so the flywheel hangs clear. Print the frame on its back (the plate on the bed).",
   "LES: the two-syringe alpha, complete."
  ],
  "table": {
   "columns": [
    "parameter",
    "value",
    "note"
   ],
   "rows": [
    [
     "crank throw",
     8,
     "stroke 16 → 2.6 mL per cylinder"
    ],
    [
     "con-rod",
     60,
     "Ø3 plain ends, H8/f7"
    ],
    [
     "V angle",
     90,
     "= phase"
    ],
    [
     "socket inner face",
     45,
     "radius from crank axis"
    ],
    [
     "min skirt radius",
     43.4,
     "≥ barrel mouth"
    ],
    [
     "rod-to-wall margin",
     0.83,
     "> 0"
    ],
    [
     "shaft",
     "Ø5 × 80",
     "2 × 625"
    ],
    [
     "rod planes (Y)",
     "9.5 / 15.5",
     "1 mm spacers"
    ]
   ]
  }
 },
 "sheet_text": "Alpha V-twin frame for two 10 mL syringes: frame, crank disc and con-rods sized so it actually runs — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/alpha-v-twin-frame/  (CC BY 4.0)\nBasis: Computed in the generator: crank throw 8, rod 60, 10 mL syringe piston (pin 8.6 above the skirt, 19 long), barrel 15.9 OD / 14.5 ID; checked over a full turn: skirt never closer than the barrel mouth, rod never within 0.5 mm of the barrel wall\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Phase: in a 90° V both con-rods ride ONE crank pin, and the 90° between the cylinders is the 90° alpha phase. (A two-pin disc with pins 90° apart is for parallel cylinders; under a 90° V it would give 0° or 180° and the engine would not run.)\n- Geometry: crank axis at the origin; both barrel axes pass through it at ±45°. Barrel sockets start at R45 so the piston (bottom of skirt 43.4 mm from the axis at bottom dead centre) never leaves the barrel, and with a 60 mm rod the rod swings at most ±7.7°, keeping 0.8 mm from the barrel wall.\n- Along the shaft (Y): 625 · boss · 625, 2 mm spacer, crank disc (6), 1 mm spacer, rod 1 (cylinder at +45°), 1 mm spacer, rod 2 (cylinder at −45°), Ø3 × 20 pin pressed 6 mm into the disc, 3 mm collar on its end. Flywheel (nut-weighted Ø100, b5) on the other end of the Ø5 × 80 shaft behind the boss.\n- Barrels slide in from the crank side, tip outward, finger flange against the socket's inner face; M3 pinch screw. Pistons: syringe-piston-10ml (no plunger). Transfer: a short tube with a mesh plug between the tips (transfer tee).\n- Foot: 2 × M5 at 50 mm into a 2020 rail; mount it at the rail's end so the flywheel hangs clear. Print the frame on its back (the plate on the bed).\n- LES: the two-syringe alpha, complete.\n\nparameter  value  note\ncrank throw  8.0  stroke 16 → 2.6 mL per cylinder\ncon-rod  60.0  Ø3 plain ends, H8/f7\nV angle  90  = phase\nsocket inner face  45.0  radius from crank axis\nmin skirt radius  43.4  ≥ barrel mouth\nrod-to-wall margin  0.83  > 0\nshaft  Ø5 × 80  2 × 625\nrod planes (Y)  9.5 / 15.5  1 mm spacers\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/\n- Wikipedia: Stirling engine (alpha configuration) — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 3 parts): https://xemstudio.com/files/hardware/alpha-v-twin-frame/index.json\nAPI: https://xemstudio.com/api/geometry?object=alpha-v-twin-frame\n",
 "sources": [
  {
   "publisher": "Long Earth Society",
   "title": "Engine builds",
   "url": "https://longearthsociety.com/engineering/",
   "formats": [
    "web",
    "video"
   ],
   "license": "LES site",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Stirling engine (alpha configuration)",
   "url": "https://en.wikipedia.org/wiki/Stirling_engine",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "syringe-pistons",
  "plastic-syringes",
  "stirling-shafts-and-rods",
  "nut-weighted-flywheels",
  "alpha-twin-crank-90",
  "ball-bearings-metric",
  "t-slot-extrusions"
 ],
 "fits": [
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "syringe-pistons",
     "why": "two 10 mL pistons on the 60 mm rods"
    },
    {
     "slug": "plastic-syringes",
     "why": "10 mL barrels in the sockets"
    },
    {
     "slug": "nut-weighted-flywheels",
     "why": "Ø100 b5 behind the boss"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "ross-yoke-kit",
     "why": "parallel-cylinder alpha, solved for 90°"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "stirling-shafts-and-rods",
     "why": "Ø5 × 80 crankshaft, Ø3 × 20 pin, spacers"
    },
    {
     "slug": "ball-bearings-metric",
     "why": "2 × 625"
    },
    {
     "slug": "alpha-twin-crank-90",
     "why": "transfer tee"
    },
    {
     "slug": "t-slot-extrusions",
     "why": "2020 rail under the foot"
    }
   ]
  }
 ],
 "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": "barrel sockets",
   "exact": "Ø15.9",
   "mates": "10 mL syringe barrel",
   "fit": "socket",
   "files": "alpha-frame-"
  },
  {
   "feature": "bearing pockets",
   "exact": "Ø16",
   "mates": "625 bearing",
   "fit": "press",
   "files": "alpha-frame-"
  },
  {
   "feature": "crank-disc bore",
   "exact": "Ø5",
   "mates": "Ø5 crankshaft (M3 grub)",
   "fit": "slide",
   "files": "alpha-crank-disc-"
  },
  {
   "feature": "crank-disc pin hole",
   "exact": "Ø3",
   "mates": "Ø3 × 20 crank pin",
   "fit": "press",
   "files": "alpha-crank-disc-"
  },
  {
   "feature": "con-rod ends",
   "exact": "Ø3",
   "mates": "Ø3 pins (turn on them)",
   "fit": "run",
   "files": "alpha-conrod-"
  }
 ],
 "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 do I get 90° phase on a two-syringe alpha Stirling?",
   "a": "Put the syringes in a 90° V and run both con-rods on one crank pin; the V angle is the phase. The alpha frame does exactly that."
  },
  {
   "q": "Why a 60 mm con-rod?",
   "a": "A shorter rod swings further and hits the inside of a 14.5 mm syringe barrel near the mouth; at 60 mm and 16 mm stroke it clears the wall by about 0.8 mm while the piston stays fully inside the barrel."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "alpha-frame-10ml",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-frame-10ml.step",
   "stl": "https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-frame-10ml.stl",
   "note": "alpha V-twin frame: Ø5 shaft in two 625s (pockets both ends of the Ø24 boss), two 10 mL barrel sockets at ±45° whose axes meet the crank axis, inner faces at R45, M3 pinch screws, foot with 2 × M5 at 50 mm for 2020"
  },
  {
   "file": "alpha-crank-disc-s16",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-crank-disc-s16.step",
   "stl": "https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-crank-disc-s16.stl",
   "note": "crank disc Ø26 × 6, Ø5 bore (H7/h6), tapped M3 grub, ONE Ø3 pin at 8 mm (stroke 16): both con-rods share it"
  },
  {
   "file": "alpha-conrod-60",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-conrod-60.step",
   "stl": "https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-conrod-60.stl",
   "note": "con-rod 60 mm, 8 wide × 5, Ø3 plain ends (H8/f7 running on the pins; print or make two): small end in the syringe piston's 5.4 mm fork"
  }
 ],
 "markdown": "https://xemstudio.com/objects/alpha-v-twin-frame/index.md"
}