# Eccentric sheaves Ø30 at 3, 5 and 8 mm offset

> What is the stroke of an eccentric sheave?

- Category: Stirling engines › Drives & mechanisms
- Kind: Hardware
- Basis: Disc on a shaft offset e from its centre; stroke = 2e
- Page: https://xemstudio.com/objects/eccentric-sheaves/ · JSON: https://xemstudio.com/api/geometry?object=eccentric-sheaves · Plain text: https://xemstudio.com/objects/eccentric-sheaves/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**Exact dimensions.** Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part.

## Notes

- A Ø30 × 8 disc with a Ø5 shaft hole offset 3, 5 or 8 mm from its centre: 6, 10 or 16 mm stroke.
- A radial Ø2.5 hole (M3 tap drill) at mid-thickness locks it to the shaft.
- It turns inside the Ø30 strap, which carries the load round its whole bore; it sits anywhere along a straight shaft without a crank throw.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| eccentric bore | Ø5 | Ø5 shaft | slide | eccentric-d30-e* |
| set-screw hole | Ø2.5 | M3 tap drill | designed | eccentric-d30-e* |

## Sizes

| file | offset e | stroke | disc | shaft |
|---|---|---|---|---|
| eccentric-d30-e3 | 3 | 6 | Ø30 × 8 | 5 |
| eccentric-d30-e5 | 5 | 10 | Ø30 × 8 | 5 |
| eccentric-d30-e8 | 8 | 16 | Ø30 × 8 | 5 |

## Where the files are

- Wikipedia: [Eccentric (mechanism)](https://en.wikipedia.org/wiki/Eccentric_(mechanism)) — web — CC BY-SA 4.0 (text)
- Long Earth Society: [Engine and rig builds on extrusion frames](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (3 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/eccentric-sheaves/index.json

- eccentric-d30-e3: [STEP](https://xemstudio.com/files/hardware/eccentric-and-strap/eccentric-d30-e3.step) · [STL](https://xemstudio.com/files/hardware/eccentric-and-strap/eccentric-d30-e3.stl) — eccentric Ø30, 3 mm offset (6 mm stroke), Ø5 shaft, Ø2.5 set-screw hole
- eccentric-d30-e5: [STEP](https://xemstudio.com/files/hardware/eccentric-and-strap/eccentric-d30-e5.step) · [STL](https://xemstudio.com/files/hardware/eccentric-and-strap/eccentric-d30-e5.stl) — eccentric Ø30, 5 mm offset (10 mm stroke), Ø5 shaft, Ø2.5 set-screw hole
- eccentric-d30-e8: [STEP](https://xemstudio.com/files/hardware/eccentric-and-strap/eccentric-d30-e8.step) · [STL](https://xemstudio.com/files/hardware/eccentric-and-strap/eccentric-d30-e8.stl) — eccentric Ø30, 8 mm offset (16 mm stroke), Ø5 shaft, Ø2.5 set-screw hole

## How it fits

### Goes in or on
- [Metric shafts Ø3 to Ø10 with D-flats and clip grooves](https://xemstudio.com/objects/metric-shafts/): Ø5 shaft, M3 grub

### Connects to
- [Split eccentric strap for Ø30 sheaves, 51 mm to the eye](https://xemstudio.com/objects/eccentric-strap/): Ø30 disc in the Ø30 strap bore

### Alternatives
- [Crank discs for a Ø5 shaft, 10 to 30 mm stroke](https://xemstudio.com/objects/crank-discs-5mm-bore/): crank and con-rod
- [Scotch yoke: slotted yoke and crank disc, 20 and 30 mm stroke](https://xemstudio.com/objects/scotch-yoke/): sine motion

## Questions

**What is the stroke of an eccentric?**

Twice the offset: the 5 mm eccentric gives 10 mm.

**Why an eccentric instead of a crank?**

It sits anywhere on a straight shaft with no throw, and the strap bears all the way round.

## Fits with

- [Split eccentric strap for Ø30 sheaves, 51 mm to the eye](https://xemstudio.com/objects/eccentric-strap/)
- [Metric shafts Ø3 to Ø10 with D-flats and clip grooves](https://xemstudio.com/objects/metric-shafts/)
- [Crank discs for a Ø5 shaft, 10 to 30 mm stroke](https://xemstudio.com/objects/crank-discs-5mm-bore/)
- [Scotch yoke: slotted yoke and crank disc, 20 and 30 mm stroke](https://xemstudio.com/objects/scotch-yoke/)
- [Swash (wobble) plates Ø40 at 10, 15 and 20°](https://xemstudio.com/objects/swash-plate-40mm/)