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Quarter-turn belt between shafts at right angles (no guide pulleys)

How does a quarter-turn belt drive work? · Hardware · basis: Xem Studio design following Brown No. 4 (1868)

Also called: quarter turn belt, half cross belt, right angle belt drive, twisted belt drive, correa de cuarto de vuelta, halbgeschränkter Riementrieb

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

sizes
5 in table

Notes

  • A belt joins pulleys on shafts at right angles with no guides: each strand must run ONTO its pulley in that pulley's mid-plane (it may leave the other pulley at an angle). That fixes the layout: each pulley's mid-plane is tangent to the other pulley's belt circle, and the drive works in one direction only.
  • Here two Ø40 × 12 plain pulleys, the second 60 mm along and 20 mm above the first; each strand twists a quarter turn. Both pulleys get 216.87° of wrap, more than an open belt — the extra contact Brown notes. Belt 12 × 1.5, inside length 271.4 mm.
  • Brown's No. 4. Pulleys without flanges, faces exactly the belt's width, so the belt can leave at an angle.
  • Parts (each has its own page): plain-flat-pulley-40x12, flat-belt-12x1-5-quarter-turn-40-40.
  • Brown's movement No. 4 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

Quarter-turn belt between shafts at right angles size chart

parametervalue
pulleys2 × Ø40 × 12, plain
shaft angle90°, non-intersecting
offsets60 mm along, 20 mm up
wrap216.87°
belt12 × 1.5, 271.4 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. 4: 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

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

Quarter-turn belt between shafts at right angles (no guide pulleys), isometric render of a generated part
Render of quarter-turn-belt-drive-mechanism-assembly from the free STEP; not to scale.

Fits with

Plain flat-belt pulley Ø40 × 12 face, Ø8 bore (no flanges), isometric render of a generated part
Plain flat-belt pulley Ø40 × 12 face, Ø8 bore (no flanges)40.0×40.0×12.0 mm★ 1 file
Quarter-turn flat belt 12 × 1.5 for two Ø40 pulleys at right angles (loop drawn on the pulleys), isometric render of a generated part
Quarter-turn flat belt 12 × 1.5 for two Ø40 pulleys at right angles (loop drawn on the pulleys)47.67×103.0×47.67 mm★ 1 file

Questions

How does a quarter-turn belt drive work?

A belt joins pulleys on shafts at right angles with no guides: each strand must run ONTO its pulley in that pulley's mid-plane (it may leave the other pulley at an angle). That fixes the layout: each pulley's mid-plane is tangent to the other pulley's belt circle, and the drive works in one direction only.

Why does a quarter-turn belt only work one way?

A belt must run onto a pulley in its mid-plane; reversed, each strand would run on at an angle and walk off the face.