Xem Studiomeasured geometry

Library › Mechanisms › Belt and friction drives ·

Crossed belt drive (driven pulley reversed), 2 : 1

Why does a crossed belt reverse the driven pulley? · Hardware · basis: Xem Studio design following Brown No. 2 (1868)

Also called: crossed belt, cross belt drive, reverse belt drive, transmisión por correa cruzada, gekreuzter Riementrieb

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

sizes
5 in table

Notes

  • Crossing the belt between two pulleys makes the driven pulley turn the opposite way to the driver; the ratio is still D₂/D₁ (80/40 = 2 : 1).
  • Both pulleys get the same wrap, π + 2·asin((R₁ + R₂)/C) = 224.05° here, more than an open belt gives the small pulley, so a crossed belt grips better; the strands rub where they cross, so it suits slow, narrow belts.
  • Drawn on the catalog flanged pulleys Ø40 and Ø80 (16 mm faces) at 160 mm centres with a 12 × 1.5 belt, inside length 531.27 mm. Brown's No. 2.
  • Parts (each has its own page): flanged-flat-pulley-40, flanged-flat-pulley-80, crossed-flat-belt-12x1-5-pulleys-40-80-c160.
  • Brown's movement No. 2 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Crossed belt drive (driven pulley reversed), 2 : 1 size chart

parametervalue
pulleysØ40 and Ø80, flanged
centres160 mm
ratio2 : 1, reversed
wrap (both)224.05°
belt12 × 1.5, 531.27 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. 2: 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

crossed-belt-drive-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.
Set it up →

Plain text: sheet.txt · JSON: /api/geometry?object=crossed-belt-drive-mechanism

Crossed belt drive (driven pulley reversed), 2 : 1, isometric render of a generated part
Render of crossed-belt-drive-mechanism-assembly from the free STEP; not to scale.

Fits with

Flanged flat-belt pulley Ø40, 16 mm face, Ø8 bore, isometric render of a generated part
Flanged flat-belt pulley Ø40, 16 mm face, Ø8 bore46.0×46.0×20.0 mm★ 1 file
Flanged flat-belt pulley Ø80, 16 mm face, Ø8 bore, isometric render of a generated part
Flanged flat-belt pulley Ø80, 16 mm face, Ø8 bore86.0×86.0×20.0 mm★ 1 file
Crossed flat belt 12 × 1.5 for Ø40 and Ø80 pulleys at 160 mm (loop drawn on the pulleys), isometric render of a generated part
Crossed flat belt 12 × 1.5 for Ø40 and Ø80 pulleys at 160 mm (loop drawn on the pulleys)223.0×83.0×12.37 mm★ 1 file

Questions

Why does a crossed belt reverse the driven pulley?

Crossing the belt between two pulleys makes the driven pulley turn the opposite way to the driver; the ratio is still D₂/D₁ (80/40 = 2 : 1).

How long is a crossed belt?

2√(C² − (R₁ + R₂)²) + (R₁ + R₂)(π + 2 asin((R₁ + R₂)/C)); it depends only on R₁ + R₂, so stepped pulleys with a constant diameter sum keep it tight.