{
 "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": "cartwright-parallel-motion-mechanism",
 "name": "Cartwright's parallel motion (twin gears and cranks)",
 "kind": "hardware",
 "category": "Mechanisms",
 "group": "Linkages",
 "year": null,
 "question": "How does Cartwright's parallel motion keep a rod straight?",
 "tags": [
  "mechanism",
  "linkages",
  "kinematics",
  "507 mechanical movements"
 ],
 "aliases": [
  "cartwright parallel motion",
  "cartwright straight line linkage",
  "twin crank straight line",
  "movimiento paralelo de Cartwright",
  "Cartwrightsche Geradführung"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": false,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/cartwright-parallel-motion-mechanism/",
 "sheet_txt": "https://xemstudio.com/objects/cartwright-parallel-motion-mechanism/sheet.txt",
 "sheet": {
  "basis": "Xem Studio design following Brown No. 328 (1868)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Two equal gears turn in opposite directions, each with a crank; equal connecting rods join the cranks to the two ends of a crosshead. By symmetry the crosshead's centre can only move on the line midway between the gears: an exact straight line.",
   "Here: module 1, 30 T gears at 30 mm, cranks 10 mm, rods 60 mm, crosshead pins 30 mm apart; at 35° the crosshead centre is 65.17 mm above the gear centres.",
   "Brown's No. 328 (Dr. Cartwright, 1787).",
   "Parts (each has its own page): crank-gear-m1-30t-pin-r10, cartwright-crosshead-30, four-bar-links, dowel-pins-metric.",
   "Brown's movement No. 328 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "gears",
     "2 × 30 T, module 1, 30 mm centres"
    ],
    [
     "crank radius",
     "10 mm"
    ],
    [
     "rods",
     "60 mm (four-bar link)"
    ],
    [
     "crosshead pins",
     "30 mm apart"
    ]
   ]
  }
 },
 "sheet_text": "Cartwright's parallel motion (twin gears and cranks) — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/cartwright-parallel-motion-mechanism/  (CC BY 4.0)\nBasis: Xem Studio design following Brown No. 328 (1868)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Two equal gears turn in opposite directions, each with a crank; equal connecting rods join the cranks to the two ends of a crosshead. By symmetry the crosshead's centre can only move on the line midway between the gears: an exact straight line.\n- Here: module 1, 30 T gears at 30 mm, cranks 10 mm, rods 60 mm, crosshead pins 30 mm apart; at 35° the crosshead centre is 65.17 mm above the gear centres.\n- Brown's No. 328 (Dr. Cartwright, 1787).\n- Parts (each has its own page): crank-gear-m1-30t-pin-r10, cartwright-crosshead-30, four-bar-links, dowel-pins-metric.\n- Brown's movement No. 328 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.\n\nparameter  value\ngears  2 × 30 T, module 1, 30 mm centres\ncrank radius  10 mm\nrods  60 mm (four-bar link)\ncrosshead pins  30 mm apart\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Henry T. Brown (1868, public domain): Five Hundred and Seven Mechanical Movements — scan on archive.org — web — Publisher's page; dimensions are facts — https://archive.org/details/fivehundredseven00browiala\n- 507movements.com: Brown's movement No. 328: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_328.html\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/cartwright-parallel-motion-mechanism/index.json\nAPI: https://xemstudio.com/api/geometry?object=cartwright-parallel-motion-mechanism\n",
 "sources": [
  {
   "publisher": "Henry T. Brown (1868, public domain)",
   "title": "Five Hundred and Seven Mechanical Movements — scan on archive.org",
   "url": "https://archive.org/details/fivehundredseven00browiala",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "507movements.com",
   "title": "Brown's movement No. 328: figure, his text and an animation",
   "url": "https://507movements.com/mm_328.html",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "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-gear-m1-30t-pin-r10",
  "cartwright-crosshead-30",
  "four-bar-links",
  "dowel-pins-metric"
 ],
 "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": [],
 "faq": [
  {
   "q": "How does Cartwright's parallel motion keep a rod straight?",
   "a": "Two equal gears turn in opposite directions, each with a crank; equal connecting rods join the cranks to the two ends of a crosshead. By symmetry the crosshead's centre can only move on the line midway between the gears: an exact straight line."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "cartwright-parallel-motion-mechanism-assembly",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/cartwright-parallel-motion-mechanism/cartwright-parallel-motion-mechanism-assembly.step",
   "stl": "https://xemstudio.com/files/hardware/cartwright-parallel-motion-mechanism/cartwright-parallel-motion-mechanism-assembly.stl",
   "note": "Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/cartwright-parallel-motion-mechanism/index.md"
}