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Helical (oblique-toothed) gears on parallel shafts, 20 : 30, helix 20°

Why are helical gears smoother than spur gears? · Hardware · basis: Xem Studio design following Brown No. 40 (1868)

Also called: helical gears, oblique tooth gears, helical gear pair, engranajes helicoidales, Schrägstirnräder

Exact dimensions. True size, with no printing tolerance added.

sizes
5 in table

Notes

  • The teeth are cut along a helix, so each tooth comes into mesh gradually from one end of the face to the other and more than one pair is always in contact: quieter, smoother and stronger than straight teeth, at the cost of an end thrust along the shafts.
  • Normal module 1.5, helix 20° (right hand on the 20-tooth, left on the 30-tooth), 12 mm face: transverse module 1.6, centre distance 39.91 mm, transverse pressure angle 21.17°. Each transverse section is an exact involute spur mesh, twisted 15.68° over the face on the pinion.
  • Brown's No. 40 (oblique-toothed gears, giving a more continuous bearing of the teeth).
  • Parts (each has its own page): helical-gear-mn1-5-20t-beta20-rh-bore6, helical-gear-mn1-5-30t-beta20-lh-bore8, linear-shafts-h6.
  • Brown's movement No. 40 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Helical (oblique-toothed) gears on parallel shafts, 20 : 30, helix 20° size chart

parametervalue
normal module1.5
teeth20 / 30
helix20°, opposite hands
face12 mm
centre distance39.91 mm

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

Henry T. Brown (1868, public domain)Five Hundred and Seven Mechanical Movements — scan on archive.orgwebPublisher's page; dimensions are facts
507movements.comBrown's movement No. 40: figure, his text and an animationwebPublisher's page; dimensions are facts

Free files

★ Free files 1 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json

helical-gears-mechanism-assemblyAssembled mechanism, all parts placed at one pose (STEP keeps each part separate)STEP · STL
Let your AI pull this. Add https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.
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Plain text: sheet.txt · JSON: /api/geometry?object=helical-gears-mechanism

Helical (oblique-toothed) gears on parallel shafts, 20 : 30, helix 20°, isometric render of a generated part
Render of helical-gears-mechanism-assembly from the free STEP; not to scale.

Fits with

Helical gear, normal module 1.5, 20 teeth, helix 20° right hand, face 12, Ø6 bore, isometric render of a generated part
Helical gear, normal module 1.5, 20 teeth, helix 20° right hand, face 12, Ø6 bore34.93×34.93×12.0 mm★ 1 file
Helical gear, normal module 1.5, 30 teeth, helix 20° left hand, face 12, Ø8 bore, isometric render of a generated part
Helical gear, normal module 1.5, 30 teeth, helix 20° left hand, face 12, Ø8 bore50.89×50.89×12.0 mm★ 1 file
Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long, isometric render of a generated part
Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long10 sizes★ 70 files

Questions

Why are helical gears smoother than spur gears?

The teeth are cut along a helix, so each tooth comes into mesh gradually from one end of the face to the other and more than one pair is always in contact: quieter, smoother and stronger than straight teeth, at the cost of an end thrust along the shafts.

What is the centre distance of helical gears?

m_n (N₁ + N₂) / (2 cos β): 1.5 × 50 / (2 cos 20°) = 39.91 mm here.