Eccentric and strap driving a slide (10 mm stroke) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/eccentric-strap-slider-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown No. 89 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- An eccentric is a crank whose pin is so large that it surrounds the shaft: a disc fixed off-centre on the shaft turns inside a strap, and the strap's rod drives whatever it is pinned to. Here the rod end is pinned to a block sliding in a straight slot, so the block reciprocates exactly like a slider-crank with crank radius = the offset and rod length = strap centre to eye.
- Catalog Ø30 eccentric with 5 mm offset (stroke 10 mm) and its split strap (eye 51 mm from the bore centre), a slide block in the 90 mm slot guide plate; drawn at 60°, block at x = 53.32 mm.
- Brown's No. 89 (eccentric and strap: the steam engine's valve drive).
- Parts (each has its own page): eccentric-and-strap, slide-block-12x6, slot-guide-plate-90, dowel-pins-metric.
- Brown's movement No. 89 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
offset  5 mm
stroke  10 mm
strap  Ø30 bore, eye at 51 mm
guide  slot plate 90, 6.2 slot

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. 89: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_089.html

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