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1:32 scale
Russian 2-6-2 S68 (=C68) class leading and tender wheels.

1,030 mm (= 3′ 4½″) diam., 10 oval spokes, vee inner rim, 75 mm apparent tread, 140 mm (=5½″) tyre width.
Hub 280 mm face dia., 36 mm out from the tyre.

Source: Russian works drawing.

Note: Also suits Hungarian MAV 4-8-0 class 424 bogie and tender wheels. 1,040 mm (= 3′ 5″) with slightly thicker tyres. (Source: Hungarian works drawing.)

Casting: 32.2 mm tread dia., 27.5 i/d., hub 1.1 mm out from the tyre
1:32 exact scale tyre thickness: 4.4 mm.

Casting prices and stock . Russian loco sets, price list

Scan of a casting in a set for a Russian 2-6-2 C68 (=S68) class, a Hungarian 4-8-0 class 424

Scan of casting P278
Scan of casting P278 machined to G1MRA Fine

Machined to G1MRA Fine standard

Cross section diagram of casting P278

Turning to the G1MRA Fine standard
Cross section diagram for casting P278 at G1MRA Fine standard
G1MRA Fine Turning diagram marked out to show the work-holding steps as used for the form tool method.

1. mount the casting with its back out and cut the small step on the back.
2. with the front out,
  cut the larger step,
  face the hub so you leave the whole top face just planed over.
    (cut a little high, then another 1 or 2 cuts of 0.01 mm until it looks right).
  face the tyre 1.1 mm below the hub.
  bore the centre just under the size of the final reamed diameter.
3. with the back out, face the back to give 5.0 mm tyre width.
4. mount the casting on a slightly loose (by diameter) mandrel between two discs, centre it, tighten up, and make the final cut with the fine form tool.

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27 Mar 2013