Triangular eccentric: curved triangle turning in a yoke (motion with dwells) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/triangular-eccentric-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown No. 91 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- A curved triangle of constant width turns about one of its corners inside a frame whose faces are exactly that width apart, so it always touches both. The frame moves to and fro, but stands still while a corner-centred arc rolls on a face: an intermittent reciprocation from continuous rotation.
- Here width 30 mm: stroke 30 mm, with a dwell at each end of the stroke; drawn at 25°.
- Brown's No. 91 (triangular eccentric giving an intermittent reciprocating motion, used in France for slide valves).
- Parts (each has its own page): triangular-eccentric-reuleaux-w30, triangular-eccentric-yoke-w30, dowel-pins-metric.
- Brown's movement No. 91 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
cam  Reuleaux triangle, width 30
pivot  one corner
stroke  30 mm
yoke opening  30 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. 91: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_091.html

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