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Eccentric and strap driving a slide (10 mm stroke)

How does an eccentric and strap give reciprocating motion? · Hardware · basis: Xem Studio design following Brown No. 89 (1868)

Also called: eccentric and strap, eccentric rod, eccentric drive, excéntrica y collar, Exzenter mit Exzenterbügel

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

sizes
4 in table

Notes

  • 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.

Eccentric and strap driving a slide size chart

parametervalue
offset5 mm
stroke10 mm
strapØ30 bore, eye at 51 mm
guideslot plate 90, 6.2 slot

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. 89: 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

eccentric-strap-slider-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=eccentric-strap-slider-mechanism

Eccentric and strap driving a slide (10 mm stroke), isometric render of a generated part
Render of eccentric-strap-slider-mechanism-assembly from the free STEP; not to scale.

Fits with

Eccentric sheaves Ø30 at 3, 5 and 8 mm offset, isometric render of a generated part
Eccentric sheaves Ø30 at 3, 5 and 8 mm offset3 sizes★ 3 files
Slide block 12 × 6.2 mm for a 6.4 mm slot, isometric render of a generated part
Slide block 12 × 6.2 mm for a 6.4 mm slot2 sizes★ 1 file
Slot guide plate 90 × 30 × 5, 6.2 mm slot (74 long), isometric render of a generated part
Slot guide plate 90 × 30 × 5, 6.2 mm slot (74 long)90.0×30.0×5.0 mm★ 1 file
Dowel pins, 2–6 mm (ISO 2338 / DIN 6325), isometric render of a generated part
Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)5 sizes★ 23 files

Questions

How does an eccentric and strap give reciprocating motion?

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.