Xem Studiomeasured geometry

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Internal gear and pinion, 60 : 20 (3 : 1, same direction)

Why does an internal gear turn the same way as its pinion? · Hardware · basis: Xem Studio design following Brown No. 34 (1868)

Also called: internal gear, ring gear and pinion, annulus and pinion, engranaje interior y piñón, Hohlrad und Ritzel

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

sizes
4 in table

Notes

  • A pinion meshing inside a ring gear: both turn the same way (an external pair reverses), the ratio is 60 : 20 = 3 : 1, and the centres are only m(N_ring − N_pinion)/2 = 20 mm apart — a compact reduction.
  • More teeth are in contact than in an external pair of the same size (the concave ring wraps the pinion), so it carries more load, as Brown notes.
  • Module 1, 20°; the ring's spaces are the exact involute tooth of a 60-tooth gear; no backlash drawn.
  • Parts (each has its own page): internal-ring-gear-m1-60t, spur-gears-module-1.
  • Brown's movement No. 34 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Internal gear and pinion, 60 : 20 size chart

parametervalue
ring60 T internal, Ø80
pinion20 T
ratio3 : 1, same direction
centre distance20 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. 34: 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

internal-gear-and-pinion-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=internal-gear-and-pinion-mechanism

Internal gear and pinion, 60 : 20 (3 : 1, same direction), isometric render of a generated part
Render of internal-gear-and-pinion-mechanism-assembly from the free STEP; not to scale.

Fits with

Internal (ring) gear, module 1, 60 teeth, Ø80, isometric render of a generated part
Internal (ring) gear, module 1, 60 teeth, Ø8080.0×80.0×8.0 mm★ 1 file
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

Why does an internal gear turn the same way as its pinion?

A pinion meshing inside a ring gear: both turn the same way (an external pair reverses), the ratio is 60 : 20 = 3 : 1, and the centres are only m(N_ring − N_pinion)/2 = 20 mm apart — a compact reduction.