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Diaphragm crosshead hub and tapped backing disc: 2 in, with the displacer rod through the centre

Name: Diaphragm crosshead hub and tapped backing disc: 2 in, with the displacer rod through the centre dimension sheet
Creator: Xem Studio
License: https://creativecommons.org/licenses/by/4.0/

How do I drive a diaphragm from a crank when the displacer rod passes through its centre? · Hardware · basis: Design values from the sealed generator: Ø20 centre clamp as the stock 2 in diaphragm disc, M2 screws (ISO 4762) in ISO 273 medium clearance holes and Ø1.6 tap-drill holes, Ø3 guide bore; the pin height comes from the crank layout

Long Earth Society build part. The hub that drives my sealed generator's membrane and guides the displacer rod. 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: 5 in table

Notes

The hub clamps the membrane from the crankcase side: a Ø20 × 3 disc with three Ø2.4 holes on Ø13 for M2 × 6 screws, heads up. Under the membrane the backing disc (Ø20 × 2, Ø5 centre hole) has three Ø1.6 holes tapped M2, so nothing stands below it into the working space.
A Ø8 boss rises to 15 mm with a Ø3 bore straight through disc and boss: the displacer rod runs in it. This 15 mm close running fit is the only way for gas between the working space and the crankcase, the bleed that lets the crankcase follow the working space's mean pressure.
A bar (z 5.5–9.5, 6 wide) runs out along +X to an arm at x 13.5–18.5 that carries the con-rod pin (Ø3 × 10, pressed) along X, 29.25 mm above the membrane face. The con-rod eye sits at x 8–13, beside the displacer's rod clevis (x ±6), so the two drives pass each other without touching.
Fits: Ø3 bore run on the Ø3 rod (the bleed); pin hole press on the dowel; disc and backing clamp the membrane.

Sizes

part	feature	value
hub	disc	Ø20 × 3, 3 × Ø2.4 on Ø13
hub	guide bore	Ø3 × 15 (run)
hub	con-rod pin	Ø3 along X at z 29.25, x 8.5–18.5
backing	disc	Ø20 × 2, Ø5 centre hole
backing	screw holes	3 × Ø1.6 (M2 tapped)

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
guide bore	Ø3 × 15	Ø3 displacer rod (crankshaft-3x60): the bleed between working space and crankcase	run	crosshead-*
con-rod pin hole	Ø3 along X in the arm	dowel-3x10	press	crosshead-*
screw holes	3 × Ø2.4 on Ø13	M2 × 6 (ISO 273 medium clearance)	designed	crosshead-*
tapped holes	3 × Ø1.6 (M2 tap drill) on Ø13	shcs-m2x6	designed	backing-*
centre hole	Ø5	Ø3 displacer rod (no contact)	designed	backing-*

Where the files are

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

ISO	ISO 273 clearance holes for bolts and screws (fine / medium / coarse)	standard	dimensions are facts verify
Wikipedia	Hagen–Poiseuille equation: plane Poiseuille flow between parallel plates (annular clearance leakage Q = π D δ³ Δp / 12 μ L)	web	CC BY-SA 4.0 (text)
Long Earth Society	Engine builds	web, video	LES site

Free files

★ Free files 2 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json

crosshead-2in-p29.25	crosshead hub: Ø20 × 3 disc with 3 × Ø2.4 on Ø13, Ø8 boss to 15, Ø3 bore 15 long (rod guide and bleed), bar z 5.5–9.5 to an arm x 13.5–18.5, Ø3 pin hole along X at 29.25	STEP · STL
backing-2in-m2-tapped	tapped backing disc Ø20 × 2: Ø5 centre hole, 3 × Ø1.6 (M2 tap drill) on Ø13	STEP · STL

Plain text: sheet.txt · JSON: /api/geometry?object=tri-clamp-diaphragm-crosshead

Diaphragm crosshead hub and tapped backing disc: 2 in, with the displacer rod through the centre, isometric render of a generated part — Render of backing-2in-m2-tapped from the free STEP; not to scale.

How it fits

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Questions

Where does gas pass between the working space and the crankcase?

Only along the Ø3 rod in the hub's 15 mm bore. With 5 µm radial clearance the mean pressures settle with a time constant of about 8 min; with 10 µm about 63 s. A cycle's leakage is negligible either way.

Why is the con-rod pin on an arm at the side?

The displacer rod runs up the axis through the hub, so the diaphragm's con-rod has its own plane beside the displacer's clevis.