Quarter-turn belt between shafts at right angles (no guide pulleys) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/quarter-turn-belt-drive-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown No. 4 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- 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.

parameter  value
pulleys  2 × Ø40 × 12, plain
shaft angle  90°, non-intersecting
offsets  60 mm along, 20 mm up
wrap  216.87°
belt  12 × 1.5, 271.4 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. 4: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_004.html

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