{
 "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": "scotch-yoke",
 "name": "Scotch yoke: slotted yoke and crank disc, 20 and 30 mm stroke",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "How do I make a Scotch yoke with 3D printed parts?",
 "tags": [
  "scotch yoke",
  "yoke",
  "slider",
  "rotary to linear",
  "mechanism",
  "motion",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "scotch yoke stl",
  "scotch yoke 3d print",
  "slotted link mechanism",
  "scotch yoke step file"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 4,
 "url": "https://xemstudio.com/objects/scotch-yoke/",
 "sheet_txt": "https://xemstudio.com/objects/scotch-yoke/sheet.txt",
 "sheet": {
  "basis": "Textbook Scotch yoke: slider displacement = r·sin θ, stroke = 2r; slot sized to a 623 bearing (OD 10) on a Ø3 crank pin, Ø5 shaft",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A crank pin rides in a slot across the yoke, so the yoke moves as a pure sine of crank angle with no connecting rod and no rod angularity.",
   "Stroke is twice the pin offset: the 20 mm crank has its pin hole at 10 mm, the 30 mm crank at 15 mm.",
   "The slot is 10 mm wide for a 623 bearing (OD 10) on a Ø3 pin through the crank disc; the rod end has a Ø3 hole for the next link.",
   "Shorter than a crank and con-rod for the same stroke; used to drive displacers and pumps."
  ],
  "table": {
   "columns": [
    "stroke",
    "parts",
    "slot",
    "crank pin offset"
   ],
   "rows": [
    [
     "20 mm",
     "yoke + crank disc",
     "10 × 30 mm",
     "10 mm"
    ],
    [
     "30 mm",
     "yoke + crank disc",
     "10 × 40 mm",
     "15 mm"
    ]
   ]
  }
 },
 "sheet_text": "Scotch yoke: slotted yoke and crank disc, 20 and 30 mm stroke — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/scotch-yoke/  (CC BY 4.0)\nBasis: Textbook Scotch yoke: slider displacement = r·sin θ, stroke = 2r; slot sized to a 623 bearing (OD 10) on a Ø3 crank pin, Ø5 shaft\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A crank pin rides in a slot across the yoke, so the yoke moves as a pure sine of crank angle with no connecting rod and no rod angularity.\n- Stroke is twice the pin offset: the 20 mm crank has its pin hole at 10 mm, the 30 mm crank at 15 mm.\n- The slot is 10 mm wide for a 623 bearing (OD 10) on a Ø3 pin through the crank disc; the rod end has a Ø3 hole for the next link.\n- Shorter than a crank and con-rod for the same stroke; used to drive displacers and pumps.\n\nstroke  parts  slot  crank pin offset\n20 mm  yoke + crank disc  10 × 30 mm  10 mm\n30 mm  yoke + crank disc  10 × 40 mm  15 mm\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Scotch yoke — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Scotch_yoke\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, 4 parts): https://xemstudio.com/files/hardware/scotch-yoke/index.json\nAPI: https://xemstudio.com/api/geometry?object=scotch-yoke\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Scotch yoke",
   "url": "https://en.wikipedia.org/wiki/Scotch_yoke",
   "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": [
  "crank-conrod-flywheel-kit",
  "ball-bearings-metric",
  "dowel-pins-metric",
  "stirling-shafts-and-rods",
  "swash-plate",
  "eccentric-and-strap"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "stirling-shafts-and-rods",
     "why": "crank disc on a Ø5 shaft"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "four-bar-links",
     "why": "Ø3 hole in the rod end"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "swash-plate",
     "why": "multi-cylinder from one shaft"
    },
    {
     "slug": "eccentric-and-strap",
     "why": "rotary to linear, no slot"
    },
    {
     "slug": "crank-conrod-flywheel-kit",
     "why": "crank and con-rod"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "ball-bearings-metric",
     "why": "623 on the crank pin, in the slot"
    },
    {
     "slug": "dowel-pins-metric",
     "why": "Ø3 crank pin"
    }
   ]
  }
 ],
 "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": "yoke slot width",
   "exact": "10",
   "mates": "623 bearing OD 10 (rolls in it)",
   "fit": "run",
   "files": "scotch-yoke-"
  },
  {
   "feature": "crank bore",
   "exact": "Ø5",
   "mates": "Ø5 shaft",
   "fit": "press",
   "files": "scotch-yoke-"
  },
  {
   "feature": "crank pin hole",
   "exact": "Ø3",
   "mates": "Ø3 pin",
   "fit": "press",
   "files": "scotch-yoke-"
  },
  {
   "feature": "rod-end hole",
   "exact": "Ø3",
   "mates": "Ø3 pin (turns in it)",
   "fit": "run",
   "files": "scotch-yoke-"
  }
 ],
 "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 is a Scotch yoke and when is it better than a con-rod?",
   "a": "A pin in a slot: the slider moves as a pure sine of crank angle with no connecting rod, so it is shorter and has no rod angularity. The pin takes the side load, so it carries a 623 bearing in the slot."
  },
  {
   "q": "How do I get the stroke I want?",
   "a": "Stroke = 2 × the crank pin offset. Pick the 20 or 30 mm crank disc, or move the pin hole to half the stroke you need."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "scotch-yoke-20-yoke",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/scotch-yoke/scotch-yoke-20-yoke.step",
   "stl": "https://xemstudio.com/files/hardware/scotch-yoke/scotch-yoke-20-yoke.stl",
   "note": "Scotch yoke slider, 20 mm stroke, 10 mm slot for a 623 bearing on the crank pin, 8 mm rod with a Ø3 end hole"
  },
  {
   "file": "scotch-yoke-20-crank",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/scotch-yoke/scotch-yoke-20-crank.step",
   "stl": "https://xemstudio.com/files/hardware/scotch-yoke/scotch-yoke-20-crank.stl",
   "note": "Scotch yoke crank disc, Ø3 pin hole at 10 mm (20 stroke), Ø5 bore"
  },
  {
   "file": "scotch-yoke-30-yoke",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/scotch-yoke/scotch-yoke-30-yoke.step",
   "stl": "https://xemstudio.com/files/hardware/scotch-yoke/scotch-yoke-30-yoke.stl",
   "note": "Scotch yoke slider, 30 mm stroke, 10 mm slot"
  },
  {
   "file": "scotch-yoke-30-crank",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/scotch-yoke/scotch-yoke-30-crank.step",
   "stl": "https://xemstudio.com/files/hardware/scotch-yoke/scotch-yoke-30-crank.stl",
   "note": "Scotch yoke crank disc, Ø3 pin hole at 15 mm (30 stroke), Ø5 bore"
  }
 ],
 "markdown": "https://xemstudio.com/objects/scotch-yoke/index.md"
}