Helical (oblique-toothed) gears on parallel shafts, 20 : 30, helix 20° — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/helical-gears-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown No. 40 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- 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.

parameter  value
normal module  1.5
teeth  20 / 30
helix  20°, opposite hands
face  12 mm
centre distance  39.91 mm

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- 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
- 507movements.com: Brown's movement No. 40: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_040.html

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/helical-gears-mechanism/index.json
API: https://xemstudio.com/api/geometry?object=helical-gears-mechanism