{
 "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": "counterweighted-crank-discs",
 "name": "Counterweighted crank discs, Ø5 bore, 10 to 30 mm stroke",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "How is a counterweighted crank disc for a small engine shaped?",
 "tags": [
  "crank disc",
  "counterweight",
  "balance",
  "crank",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "counterweighted crank disc",
  "stirling engine counterweight",
  "balanced crank disc",
  "crank balance small engine"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 5,
 "url": "https://xemstudio.com/objects/counterweighted-crank-discs/",
 "sheet_txt": "https://xemstudio.com/objects/counterweighted-crank-discs/sheet.txt",
 "sheet": {
  "basis": "Crank disc ending just past the pin and thickened opposite it; pin at stroke / 2, Ø5 bore, M3 grub",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A 6 mm disc (Ø32, 32, 34, 39, 44 for 10–30 mm stroke) with the Ø3 pin hole at half the stroke. On the pin side the disc ends 6 mm past the pin centre, with a Ø10 boss round the pin.",
   "Opposite the pin a raised segment 4.8 thick (10.8 overall) carries the counterweight; the description sizes it at about 50 % of a con-rod and piston at the pin radius.",
   "Ø5 bore and a radial Ø2.5 hole (M3 tap drill) at mid-thickness for a grub on the shaft's flat.",
   "Balance condition: m_cw × r_cw = m_rotating × r_pin + 0.5 × m_reciprocating × r_pin. A crank that stops at any angle when spun bare is statically balanced; at 200–600 rpm that is enough."
  ],
  "table": {
   "columns": [
    "file",
    "stroke",
    "pin offset",
    "disc Ø",
    "thickness",
    "envelope"
   ],
   "rows": [
    [
     "cw-crank-disc-stroke10",
     10,
     5,
     32,
     "6 / 10.8",
     "27 × 32"
    ],
    [
     "cw-crank-disc-stroke15",
     15,
     7.5,
     32,
     "6 / 10.8",
     "29.5 × 32"
    ],
    [
     "cw-crank-disc-stroke20",
     20,
     10,
     34,
     "6 / 10.8",
     "33 × 34"
    ],
    [
     "cw-crank-disc-stroke25",
     25,
     12.5,
     39,
     "6 / 10.8",
     "38 × 39"
    ],
    [
     "cw-crank-disc-stroke30",
     30,
     15,
     44,
     "6 / 10.8",
     "43 × 44"
    ]
   ]
  }
 },
 "sheet_text": "Counterweighted crank discs, Ø5 bore, 10 to 30 mm stroke — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/counterweighted-crank-discs/  (CC BY 4.0)\nBasis: Crank disc ending just past the pin and thickened opposite it; pin at stroke / 2, Ø5 bore, M3 grub\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A 6 mm disc (Ø32, 32, 34, 39, 44 for 10–30 mm stroke) with the Ø3 pin hole at half the stroke. On the pin side the disc ends 6 mm past the pin centre, with a Ø10 boss round the pin.\n- Opposite the pin a raised segment 4.8 thick (10.8 overall) carries the counterweight; the description sizes it at about 50 % of a con-rod and piston at the pin radius.\n- Ø5 bore and a radial Ø2.5 hole (M3 tap drill) at mid-thickness for a grub on the shaft's flat.\n- Balance condition: m_cw × r_cw = m_rotating × r_pin + 0.5 × m_reciprocating × r_pin. A crank that stops at any angle when spun bare is statically balanced; at 200–600 rpm that is enough.\n\nfile  stroke  pin offset  disc Ø  thickness  envelope\ncw-crank-disc-stroke10  10  5.0  32  6 / 10.8  27 × 32\ncw-crank-disc-stroke15  15  7.5  32  6 / 10.8  29.5 × 32\ncw-crank-disc-stroke20  20  10.0  34  6 / 10.8  33 × 34\ncw-crank-disc-stroke25  25  12.5  39  6 / 10.8  38 × 39\ncw-crank-disc-stroke30  30  15.0  44  6 / 10.8  43 × 44\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Engine balance — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Engine_balance\n- Wikipedia: Crankshaft — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Crankshaft\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, 5 parts): https://xemstudio.com/files/hardware/counterweighted-crank-discs/index.json\nAPI: https://xemstudio.com/api/geometry?object=counterweighted-crank-discs\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Engine balance",
   "url": "https://en.wikipedia.org/wiki/Engine_balance",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Crankshaft",
   "url": "https://en.wikipedia.org/wiki/Crankshaft",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "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": [
  "crank-discs-5mm-bore",
  "crank-webs-5mm-bore",
  "bolt-on-counterweights",
  "connecting-rods-623",
  "crank-stands-625"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "stirling-crankshafts",
     "why": "Ø5 bore, M3 grub on the flat"
    },
    {
     "slug": "crank-stands-625",
     "why": "on the shaft beside the 625 stand"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "connecting-rods-623",
     "why": "623 on the Ø3 pin"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "crank-discs-5mm-bore",
     "why": "plain disc"
    }
   ]
  }
 ],
 "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": "disc bore",
   "exact": "Ø5",
   "mates": "Ø5 crankshaft (M3 grub)",
   "fit": "slide",
   "files": "cw-crank-disc-"
  },
  {
   "feature": "disc pin hole",
   "exact": "Ø3",
   "mates": "Ø3 crank pin",
   "fit": "press",
   "files": "cw-crank-disc-"
  },
  {
   "feature": "disc grub hole",
   "exact": "Ø2.5",
   "mates": "M3 tap drill",
   "fit": "designed",
   "files": "cw-crank-disc-"
  }
 ],
 "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 much counterweight does a single-cylinder engine need?",
   "a": "Enough that mass × radius opposite the pin equals the rotating mass plus about half the reciprocating mass at the pin radius."
  },
  {
   "q": "Why does my Stirling engine walk across the table?",
   "a": "The crank is out of balance: the piston and con-rod pull outward once a turn. A counterweight opposite the pin cancels it."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "cw-crank-disc-stroke10",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke10.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke10.stl",
   "note": "counterweighted crank disc, 10 mm stroke (pin at 5.0), Ø5 bore, M3 grub, mass opposite the pin ≈ 50% of the con-rod+piston at the pin radius"
  },
  {
   "file": "cw-crank-disc-stroke15",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke15.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke15.stl",
   "note": "counterweighted crank disc, 15 mm stroke (pin at 7.5), Ø5 bore, M3 grub, mass opposite the pin ≈ 50% of the con-rod+piston at the pin radius"
  },
  {
   "file": "cw-crank-disc-stroke20",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke20.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke20.stl",
   "note": "counterweighted crank disc, 20 mm stroke (pin at 10.0), Ø5 bore, M3 grub, mass opposite the pin ≈ 50% of the con-rod+piston at the pin radius"
  },
  {
   "file": "cw-crank-disc-stroke25",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke25.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke25.stl",
   "note": "counterweighted crank disc, 25 mm stroke (pin at 12.5), Ø5 bore, M3 grub, mass opposite the pin ≈ 50% of the con-rod+piston at the pin radius"
  },
  {
   "file": "cw-crank-disc-stroke30",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke30.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke30.stl",
   "note": "counterweighted crank disc, 30 mm stroke (pin at 15.0), Ø5 bore, M3 grub, mass opposite the pin ≈ 50% of the con-rod+piston at the pin radius"
  }
 ],
 "markdown": "https://xemstudio.com/objects/counterweighted-crank-discs/index.md"
}