Xem Studiomeasured geometryLibrary › Mechanisms › Belt and friction drives ·
Jockey (tightening) pulley engaging a slack belt
How does a jockey pulley start and stop a belt drive? · Hardware · basis: Xem Studio design following Brown No. 5 (1868)
Also called: jockey pulley, belt tightener, idler pulley clutch, tensioner pulley, polea tensora (embrague por tensor), Spannrolle (Riemenspanner)
Exact dimensions. True size, with no printing tolerance added.
- sizes
- 5 in table
Notes
- The belt is made a little long, so it slips idle on the pulleys; a pulley on a lever (the jockey or tightener) pressed on the back of the slack strand takes up the slack and the drive starts. Lift the lever and it stops — a clutch without moving the belt.
- Here Ø40 and Ø80 pulleys at 140 mm, a 16 × 1.5 belt of 472.33 mm (0.98 mm longer than an open belt) and a Ø30 jockey pressing the upper strand in 8 mm. The jockey also adds wrap on the small pulley: 169.91° instead of 196.43°.
- Brown's No. 5. Put the jockey on the slack side (here the upper strand when the small pulley drives clockwise).
- Parts (each has its own page): flanged-flat-pulley-40, flanged-flat-pulley-80, flanged-flat-pulley-30-bore6, flat-belt-16x1-5-jockey-drive-40-80-c140, jockey-lever-bore6, dowel-pins-metric.
- Brown's movement No. 5 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.
Jockey (tightening) pulley engaging a slack belt size chart
| parameter | value |
|---|---|
| pulleys | Ø40 and Ø80 at 140 mm |
| jockey | Ø30, 8 mm deflection |
| belt | 16 × 1.5, 472.33 mm |
| wrap on Ø40 | 169.91° |
| lever | 51.48 mm + 40 mm handle |
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.org | web | Publisher's page; dimensions are facts |
| 507movements.com | Brown's movement No. 5: figure, his text and an animation | web | Publisher'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
| jockey-pulley-belt-tightener-mechanism-assembly | Assembled mechanism, all parts placed at one pose (STEP keeps each part separate) | STEP · STL |
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.Plain text: sheet.txt · JSON: /api/geometry?object=jockey-pulley-belt-tightener-mechanism
Fits with
Questions
How does a jockey pulley start and stop a belt drive?
The belt is made a little long, so it slips idle on the pulleys; a pulley on a lever (the jockey or tightener) pressed on the back of the slack strand takes up the slack and the drive starts. Lift the lever and it stops — a clutch without moving the belt.