{
 "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": "bell-cranks",
 "name": "Bell cranks: 30 × 30 and 20 × 40 mm arms at 90°",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "How do I make a bell crank with 3D printed parts?",
 "tags": [
  "bell crank",
  "lever",
  "linkage",
  "mechanism",
  "motion",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "bell crank 3d print",
  "bell crank stl",
  "90 degree lever"
 ],
 "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/bell-cranks/",
 "sheet_txt": "https://xemstudio.com/objects/bell-cranks/sheet.txt",
 "sheet": {
  "basis": "Bell crank lever: output motion = input × (output arm / input arm); 90° between arms; Ø10 pivot pocket for a 623 bearing",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Turns a push or pull through 90°. The 30 × 30 crank keeps the same travel; the 20 × 40 doubles it (or halves it, driven the other way).",
   "Pivot is a Ø10 pocket for a 623 bearing (OD 10); arm ends have Ø3 holes for pins and links.",
   "Used in the beta Stirling bell-crank drive to phase the displacer and piston."
  ],
  "table": {
   "columns": [
    "arms",
    "angle",
    "ratio",
    "pivot"
   ],
   "rows": [
    [
     "30 × 30 mm",
     "90°",
     "1:1",
     "Ø10 (623)"
    ],
    [
     "20 × 40 mm",
     "90°",
     "1:2",
     "Ø10 (623)"
    ]
   ]
  }
 },
 "sheet_text": "Bell cranks: 30 × 30 and 20 × 40 mm arms at 90° — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/bell-cranks/  (CC BY 4.0)\nBasis: Bell crank lever: output motion = input × (output arm / input arm); 90° between arms; Ø10 pivot pocket for a 623 bearing\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Turns a push or pull through 90°. The 30 × 30 crank keeps the same travel; the 20 × 40 doubles it (or halves it, driven the other way).\n- Pivot is a Ø10 pocket for a 623 bearing (OD 10); arm ends have Ø3 holes for pins and links.\n- Used in the beta Stirling bell-crank drive to phase the displacer and piston.\n\narms  angle  ratio  pivot\n30 × 30 mm  90°  1:1  Ø10 (623)\n20 × 40 mm  90°  1:2  Ø10 (623)\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Bellcrank — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Bellcrank\n- Long Earth Society: Engine and rig builds on extrusion frames — 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/bell-cranks/index.json\nAPI: https://xemstudio.com/api/geometry?object=bell-cranks\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Bellcrank",
   "url": "https://en.wikipedia.org/wiki/Bellcrank",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine and rig builds on extrusion frames",
   "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": [
  "four-bar-links",
  "ball-bearings-metric",
  "dowel-pins-metric",
  "stirling-configurations-guide"
 ],
 "fits": [
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "four-bar-links",
     "why": "Ø3 arm holes"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "ball-bearings-metric",
     "why": "623 in the Ø10 pivot pocket"
    },
    {
     "slug": "dowel-pins-metric",
     "why": "Ø3 pivot and arm pins"
    }
   ]
  }
 ],
 "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": "pivot pocket",
   "exact": "Ø10",
   "mates": "623 bearing OD 10",
   "fit": "press",
   "files": "all"
  },
  {
   "feature": "arm holes",
   "exact": "Ø3",
   "mates": "Ø3 pins (turn in them)",
   "fit": "run",
   "files": "all"
  }
 ],
 "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": "What does a bell crank do?",
   "a": "It changes the direction of a push or pull, usually by 90°, and scales the travel by the ratio of its arms."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "bell-crank-30x30-90",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/bell-cranks/bell-crank-30x30-90.step",
   "stl": "https://xemstudio.com/files/hardware/bell-cranks/bell-crank-30x30-90.stl",
   "note": "bell crank, 30 × 30 mm arms at 90°, Ø10 pocket for a 623 bearing pivot, Ø3 arm holes"
  },
  {
   "file": "bell-crank-20x40-90",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/bell-cranks/bell-crank-20x40-90.step",
   "stl": "https://xemstudio.com/files/hardware/bell-cranks/bell-crank-20x40-90.stl",
   "note": "bell crank, 20 × 40 mm arms (2:1) at 90°, Ø10 pivot pocket, Ø3 arm holes"
  }
 ],
 "markdown": "https://xemstudio.com/objects/bell-cranks/index.md"
}