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Spur gear pair, module 1, 20 : 40 teeth (2 : 1)

How do two spur gears change speed and direction? · Hardware · basis: Xem Studio design following Brown No. 24 (1868)

Also called: spur gears, gear pair, gear ratio 2:1, spur gear mesh, par de engranajes rectos, Stirnradpaar

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

sizes
5 in table

Notes

  • Two involute spur gears on parallel shafts: the speed ratio is the inverse tooth ratio (20 : 40 → output at half speed, double torque) and the shafts turn in opposite directions.
  • Module 1, 20° pressure angle, centre distance m(N₁ + N₂)/2 = 30 mm exactly; teeth meet on the pitch line with no backlash drawn.
  • Brown's figure 24 is the plain spur pair, the base of every gear train in the book.
  • Parts (each has its own page): spur-gears-module-1.
  • Brown's movement No. 24 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Spur gear pair, module 1, 20 : 40 teeth size chart

parametervalue
module1
teeth20 / 40
ratio2 : 1
centre distance30 mm
face width8 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. 24: figure, his text and an animationwebPublisher's page; dimensions are facts

Free files

★ Free files 1 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json

spur-gear-pair-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=spur-gear-pair-mechanism

Spur gear pair, module 1, 20 : 40 teeth (2 : 1), isometric render of a generated part
Render of spur-gear-pair-mechanism-assembly from the free STEP; not to scale.

Fits with

Spur gears, module 1: 10 to 80 teeth (20° involute), isometric render of a generated part
Spur gears, module 1: 10 to 80 teeth (20° involute)26 sizes★ 26 files

Questions

How do two spur gears change speed and direction?

Two involute spur gears on parallel shafts: the speed ratio is the inverse tooth ratio (20 : 40 → output at half speed, double torque) and the shafts turn in opposite directions.

What is the centre distance of a 20 and 40 tooth module 1 pair?

30 mm: m × (20 + 40) / 2.