# Linear alternator back-iron sleeve Ø60.5 × Ø52.5 × 30

> What size is the back iron of the linear alternator?

- Category: Stirling engines › Free-piston
- Kind: Hardware
- Basis: Tube at the sizes in the generator: OD 60.5, bore 52.5 (the bobbin flange OD), length 30 (the bobbin length)
- Page: https://xemstudio.com/objects/linear-alternator-back-iron-sleeve/ · JSON: https://xemstudio.com/api/geometry?object=linear-alternator-back-iron-sleeve · Plain text: https://xemstudio.com/objects/linear-alternator-back-iron-sleeve/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

- The outer flux return of the alternator: a tube Ø60.5 × Ø52.5 bore × 30 long.
- The bobbin slides into its bore (Ø52.5, fit: slide) and it sits in the housing's Ø60.5 pocket (fit: socket) on a 2 mm ledge, held down by the cap ring.
- The magnetic gap from magnet face to the sleeve is 8.8 mm.

## 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 |
|---|---|---|---|---|
| sleeve in the housing | Ø60.5 | housing pocket | socket | alt-back-iron-* |

## Sizes

| parameter | value |
|---|---|
| outside | 60.5 |
| bore | 52.5 |
| length | 30 |

## Where the files are

- NASA (NTRS, public domain): [Linear alternator design for free-piston Stirling convertors (2005)](https://ntrs.nasa.gov/search?q=20050182934) — PDF — US Government work, public domain
- NASA (NTRS, public domain): [Sunpower/NASA 80 We free-piston Stirling convertor (2002)](https://ntrs.nasa.gov/search?q=20020047256) — PDF — US Government work, public domain
- Wikipedia: [Linear alternator](https://en.wikipedia.org/wiki/Linear_alternator) — web — CC BY-SA 4.0 (text)
- Wikipedia: [Free-piston engine](https://en.wikipedia.org/wiki/Free-piston_engine) — web — CC BY-SA 4.0 (text)
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (1 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/linear-alternator-back-iron-sleeve/index.json

- alt-back-iron-sleeve: [STEP](https://xemstudio.com/files/hardware/linear-alternator-kit/alt-back-iron-sleeve.step) · [STL](https://xemstudio.com/files/hardware/linear-alternator-kit/alt-back-iron-sleeve.stl) — back-iron sleeve Ø60.5 × Ø52.5 × 30: closes the magnet flux outside the coils; the bobbin slides in, the sleeve sits in the housing

## How it fits

### Goes in or on
- [Linear alternator housing for Ø80 and Ø100 flexures (2 in / 3 in)](https://xemstudio.com/objects/linear-alternator-housing/): in the Ø60.5 pocket

### Connects to
- [Linear alternator bobbin: Ø37 bore, two 10 mm bays](https://xemstudio.com/objects/linear-alternator-bobbin/): bobbin in the Ø52.5 bore
- [Linear alternator cap ring, Ø96 and Ø116](https://xemstudio.com/objects/linear-alternator-cap-ring/): held down by the cap ring

### Alternatives
- [Schedule 40 pipe and PVC fittings, 1/2 to 2 inch](https://xemstudio.com/objects/schedule-40-pipe/): NPS 2 Sch 40 pipe has a 52.5 bore

## Questions

**What does the back-iron sleeve do?**

It closes the magnets' flux outside the coils so the flux crosses the windings.

**What size is the back-iron sleeve?**

Ø60.5 outside, Ø52.5 bore, 30 long.

## Fits with

- [Linear alternator bobbin: Ø37 bore, two 10 mm bays](https://xemstudio.com/objects/linear-alternator-bobbin/)
- [Linear alternator housing for Ø80 and Ø100 flexures (2 in / 3 in)](https://xemstudio.com/objects/linear-alternator-housing/)
- [Schedule 40 pipe and PVC fittings, 1/2 to 2 inch](https://xemstudio.com/objects/schedule-40-pipe/)