Free-piston mover for a 2 in honed spool: piston and alternator magnets in one, Ø48.00 × 130 — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/free-piston-mover-2in/  (CC BY 4.0)
Basis: Ø48.00 to the honed spool; magnet rows and pitch from the alternator design in tools/gen_ta_power.py
Catalog version: 2026-10-20

Sizes: see table below
- The piston and the alternator's moving part are one: a 12-sided core carries 4 rows of 12 block magnets (30 × 10 × 4, magnetised through 4), rows alternately N and S outward at 32 mm pitch, and a sleeve Ø48.00 / Ø47 slides over them and runs in the honed bore. The core is the magnets' return path, so it has to carry magnetic flux; what it and the sleeve are made of is the builder's choice within that.
- The crown is closed; an M4 threaded rod screws into it from inside the Ø20 bore and carries the two flexure stacks below. Moving mass with the magnets, rod and hub parts: about 1.39 kg (core and sleeve counted at 7.8 g/cm³, magnets at 7.5).
- Design stroke ±8 mm: the 30 mm magnet rows stay fully over their 14 mm coils that far.
- Fits: sleeve OD is the clearance seal in the honed bore (run); the sleeve's bore slides over the core's flanges (press); the magnets sit on the flats (bonded, designed).

feature  value
length  130
sleeve  Ø48.00 / Ø47
magnets  4 × 12 blocks 30 × 10 × 4
row pitch  32
moving mass  ≈ 1.39 kg
design stroke  ±8

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Appl. Phys. Lett. (S. Backhaus, E. Tward, M. Petach): Traveling-wave thermoacoustic electric generator, APL 85, 1085 (2004): a thermoacoustic-Stirling engine driving linear alternators, 18 % heat to electricity — web — journal article; cited [verify license at link] — https://doi.org/10.1063/1.1781739
- Applied Energy (Z. Wu, G. Yu, L. Zhang, W. Dai, E. Luo): Development of a 3 kW double-acting thermoacoustic Stirling electric generator, 136, 866-872 (2014): three engines and three linear alternators in a loop, 5 MPa helium, 86 Hz, 1.57 kW electric, 16.8 % — web — journal article; cited [verify license at link] — https://doi.org/10.1016/j.apenergy.2014.04.105
- Xem Studio: tools/gen_ta_power.py: the network model and every dimension on this page — code — CC BY 4.0 — https://xemstudio.com/
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 2 parts): https://xemstudio.com/files/hardware/free-piston-mover-2in/index.json
API: https://xemstudio.com/api/geometry?object=free-piston-mover-2in