Diagrams Index . Home
1:32 scale
P74
BR standard bogie wheel.

3′ 0″ diam., 9 oval spokes, vee inner rim, 3½″ apparent tread, 6″ tyre width.
Hub 10¼″ face dia., spreading to 14¼″ at the base rim, 1½″ out from the tyre.

Sources: 4MT measured direct and BR Derby works drawing.

Casting: 28.6 mm tread dia., 22.9 mm i/d, hub 1.1 mm out from the tyre.
Tyre widths for exact scale models at 1:32, 6″ = 4.8 mm.

Casting prices and stock . BR loco sets, price list

Scan of a casting in a set for a BR 4-6-0 4MT . 2-6-4T 4MT

Scan of casting P74
Scan of casting P74 machined to G1MRA Fine
Scan of casting P74 machined to 'dead scale'

Cross section diagram of casting P74

Cross section diagram of casting P74 for G1MRA Fine

Cross section diagram of casting P74 for 'dead scale'
Turning diagrams 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 a small rounded edge outside the flat surface
    (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 your chosen the 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 appropriate form tool.



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27 Mar 2013