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Free-piston power piston: Ø48 clearance-seal land, 40-magnet carrier, top plate and tube rod

Name: Free-piston power piston: Ø48 clearance-seal land, 40-magnet carrier, top plate and tube rod dimension sheet
Creator: Xem Studio
License: https://creativecommons.org/licenses/by/4.0/

What does the power piston of a moving-magnet free-piston generator look like? · Hardware · basis: Design values of the free-piston generator: running fit in the 48.00 bore over a 30 mm land; four magnet rows S N N S facing out; moving mass from the CAD at 7.9 g/cm³ and 7.5 g/cm³ (magnets)

Long Earth Society build part. The power piston of my free-piston generator. The engines

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. Mating features

sizes: 6 in table

Notes

The piston is also the alternator's mover. Its lower 30 mm is the seal land, a running fit in the bored spool (the clearance seal between working space and bounce space); above it a Ø47 carrier (0.5 radial gap, no contact) holds 40 Ø12 × 3 disc magnets in four rows, faces out: S, N, N, S from the crown up.
The carrier's body is the magnetic return between the rows, so it must be magnetically soft; the rest of the piston only has to be stiff and light. Moving mass with tube rod, collars and magnets: 918 g.
The displacer rod runs through the Ø12 hub bore (a running fit 76 mm long, also a seal); the Ø23 crown pocket clears leaf B's collar. The top plate closes the carrier bore, carries the tube rod and vents the piston's inside to the bounce space.
The tube rod carries the piston's two leaves (joints C and D) on four Ø28 collars.

Sizes

part	size
seal land	Ø48.00 × 30
carrier	Ø47 × 60, bore Ø30
magnets	40 × Ø12 × 3, rows S N N S at 14 pitch
hub bore	Ø12, 76 long
tube rod	Ø18 / Ø14 × 142.15
moving mass	918 g

Mating features

Drawn at the exact size. Open press, slide, run and socket features by your process's clearance; leave designed gaps and clamp fits as drawn.

feature	exact	mates with	fit	files
seal land	Ø48.00 × 30	S4 bore Ø48.00 (clearance seal)	run	fpse-piston-48*
carrier OD	Ø47.0	S4 bore (0.5 radial gap, no contact)	designed	fpse-piston-48*
magnet pockets	40 × Ø12 × 3 radial	Ø12 × 3 disc magnets	press	fpse-piston-48*
hub bore	Ø12 × 76	displacer rod (seal and guide)	run	fpse-piston-48*
carrier bore top	Ø30 × 4	top plate	press	fpse-piston-48*
crown pocket	Ø23 × 6	displacer collar Ø20 (no contact)	designed	fpse-piston-48*
bore	Ø18	tube rod	press	fpse-piston-top*
OD	Ø18	top plate bore, leaf hubs, collars	slide	fpse-tube-rod*
bore	Ø14	displacer rod Ø12 (no contact)	designed	fpse-tube-rod*

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

K&J Magnetics	Neodymium magnet specifications: N42 Br 1.30–1.32 T, density 7.4–7.5 g/cm³	web	maker page; values are facts verify
Long Earth Society	Engine builds	web, video	LES site

Free files

★ Free files 3 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json

fpse-piston-48-40mag	piston body: seal land Ø48.00 × 30 (crown 8 with a Ø23 × 6 pocket, skirt bore Ø44), magnet carrier Ø47 × 60 (bore Ø30) with 4 rows × 10 radial pockets Ø12 × 3 at z 37, 51, 65, 79, hub tube Ø20 / Ø12 (the rod's running fit)	STEP · STL
fpse-piston-top-plate	piston top plate Ø30 × 4 in the carrier bore on the hub's end, Ø18 bore for the tube rod, 4 × Ø2 vents	STEP · STL
fpse-tube-rod-18x14	tube rod Ø18 / Ø14 × 142.15: from the piston's hub to above leaf D	STEP · STL

Plain text: sheet.txt · JSON: /api/geometry?object=fpse-power-piston

Free-piston power piston: Ø48 clearance-seal land, 40-magnet carrier, top plate and tube rod, isometric render of a generated part — Render of fpse-piston-top-plate from the free STEP; not to scale.

How it fits

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Questions

Why is the piston the mover?

It keeps the moving mass in one part, needs no separate rod to a mover, and puts the magnets right inside the bored wall, where the stator outside can reach them through 1.9 mm of gap and wall.