{
 "version": "2026-10-20",
 "license": "Dimension sheets: CC BY 4.0. Standard and published-size files: CC BY 4.0. Xem Studio's own designs (files_license = Xem Studio Design License): free to use and sell things from, not to redistribute as files — https://xemstudio.com/license/. Other publishers' files: their own license, linked beside them.",
 "slug": "double-helical-gears-mechanism",
 "name": "Double-helical (herringbone) gears, 20 : 30, helix 20°",
 "kind": "hardware",
 "category": "Mechanisms",
 "group": "Gears",
 "year": null,
 "question": "Why use double-helical (herringbone) gears?",
 "tags": [
  "mechanism",
  "gears",
  "kinematics",
  "507 mechanical movements"
 ],
 "aliases": [
  "herringbone gears",
  "double helical gears",
  "chevron gears",
  "engranajes bihelicoidales",
  "Pfeilverzahnung"
 ],
 "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/double-helical-gears-mechanism/",
 "sheet_txt": "https://xemstudio.com/objects/double-helical-gears-mechanism/sheet.txt",
 "sheet": {
  "basis": "Xem Studio design following Brown No. 41 (1868)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Each gear has two rows of oblique teeth of opposite hand meeting at the middle of the face: like single helical gears the teeth engage gradually and several are always in contact, but the two axial thrusts cancel, so no thrust bearing is needed.",
   "Here normal module 1.5, 20 and 30 teeth, helix 20° each way, 16 mm face; centre distance (r₁ + r₂) = 39.91 mm with the transverse module 1.6. Every transverse section is an exact involute spur mesh.",
   "Brown's No. 41 shows a second pair of oblique-toothed wheels; this page draws the double-helical form, the answer to the end thrust of No. 40.",
   "Parts (each has its own page): double-helical-gear-mn1-5-20t-beta20-bore6, double-helical-gear-mn1-5-30t-beta20-bore8, linear-shafts-h6.",
   "Brown's movement No. 41 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "normal module",
     "1.5"
    ],
    [
     "teeth",
     "20 / 30"
    ],
    [
     "helix",
     "20°, both hands on each gear"
    ],
    [
     "face",
     "16 mm"
    ],
    [
     "centre distance",
     "39.91 mm"
    ]
   ]
  }
 },
 "sheet_text": "Double-helical (herringbone) gears, 20 : 30, helix 20° — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/double-helical-gears-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)\nBasis: Xem Studio design following Brown No. 41 (1868)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Each gear has two rows of oblique teeth of opposite hand meeting at the middle of the face: like single helical gears the teeth engage gradually and several are always in contact, but the two axial thrusts cancel, so no thrust bearing is needed.\n- Here normal module 1.5, 20 and 30 teeth, helix 20° each way, 16 mm face; centre distance (r₁ + r₂) = 39.91 mm with the transverse module 1.6. Every transverse section is an exact involute spur mesh.\n- Brown's No. 41 shows a second pair of oblique-toothed wheels; this page draws the double-helical form, the answer to the end thrust of No. 40.\n- Parts (each has its own page): double-helical-gear-mn1-5-20t-beta20-bore6, double-helical-gear-mn1-5-30t-beta20-bore8, linear-shafts-h6.\n- Brown's movement No. 41 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.\n\nparameter  value\nnormal module  1.5\nteeth  20 / 30\nhelix  20°, both hands on each gear\nface  16 mm\ncentre distance  39.91 mm\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. 41: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_041.html\n\nFree files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/double-helical-gears-mechanism/index.json\nAPI: https://xemstudio.com/api/geometry?object=double-helical-gears-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. 41: figure, his text and an animation",
   "url": "https://507movements.com/mm_041.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": [
  "double-helical-gear-mn1-5-20t-beta20-bore6",
  "double-helical-gear-mn1-5-30t-beta20-bore8",
  "linear-shafts-h6"
 ],
 "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": "Why use double-helical (herringbone) gears?",
   "a": "Each gear has two rows of oblique teeth of opposite hand meeting at the middle of the face: like single helical gears the teeth engage gradually and several are always in contact, but the two axial thrusts cancel, so no thrust bearing is needed."
  }
 ],
 "files_license": {
  "name": "Xem Studio Design License",
  "holder": "Xem Studio",
  "url": "https://xemstudio.com/license/",
  "note": "Xem Studio's own design: free to use, print, modify and sell things made from it; not to be republished or redistributed as files."
 },
 "offers": [
  {
   "file": "double-helical-gears-mechanism-assembly",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "Xem Studio Design License",
   "step": "https://xemstudio.com/files/hardware/double-helical-gears-mechanism/double-helical-gears-mechanism-assembly.step",
   "stl": "https://xemstudio.com/files/hardware/double-helical-gears-mechanism/double-helical-gears-mechanism-assembly.stl",
   "note": "Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/double-helical-gears-mechanism/index.md"
}