Re: Pennsy A3 Switcher DRIVE WHEELS

In _Live Steam_ magazine, a series of articles, _Building
a Live Steam Locomotive, The Pennsylvania A3 Switcher_,
Kozo Hiroka outlines the preparation of the Driving Wheels
in Part 11, May/June 1994.
The pattern for the Driving Wheels is made with the intent
of casting the wheels in grey iron. If the homeshop caster
attempts to cast these wheels in bronze, especially Silicon
Bronze, problems may be encountered with cracking of the
spoke webs if special setup is not observed during casting.
In Part 12 of the project articles, it is noted that the
wheels and pattern are available from Power Model Supply Co.
cast in Silicon Bronze. I am the caster of these wheels and
what follows is a detailed listing of the setup parameters
used to achieve defect-free castings. Kramer #876 bronze is
the alloy used. If further information is needed, reference
pattern number LWR-PW when contacting me.

Overview
The pattern is step-gated and a two riser, single riser basin
is used.

Details
1. Very firmly, hand-press new facing sand into the web
cavities.
2. Set the runner gate, 4"x3/4" half-round. The runner is
placed tangential to the pattern edge with the short webs and
narrow rim section.
3. Ram the drag using a medium-hard ram,
4. Roll drag and set step-gate, 3/4"x1 1/2" half-round, from
end of runner gate to pattern at center of narrow rim section.
Step-gate should overlap pattern about 3/8".
5. Set two 1" diameter riser forms, one at center of pattern
and one at center of wide rim section.
5a. Set sprue form, 3/4" diameter, on runner at end opposite
the step-gate.
6. Ram cope.
7. Cut/form pour basin.
8. Cut/form a single riser basin at the top of the riser forms.
Taper the basin to within 1/2" of pattern, leaving a sand bridge
at the bottom of the riser forms, 3/8" to 1/2" tall.
8a. Remove sprue and riser forms.
9. Part the flask sections.
10. Remove step-gate and runner forms.
11. Print rap the pattern. Do NOT side rap.
11a. Carefully pull the pattern.
12. Brush clean all cavity edges and air blow the cope/drag.
12a. Close flask.
13. Pour metal. Use a 3 minute superheat for silicon bronze.
(Assumes a propane fired furnace and #8 crucible. Three to four
castings can be poured per melt, depending on size of basins).
14. Hot-top riser basin during pour operation.
15. Minimum cool time before shakeout: 1 hour.

Remarks
The reason for this elaborate setup when casting the wheels in
Silicon Bronze is that the pattern was designed for grey iron
castings. With iron, the cast could be made with a simple center
drop-gate without any problems. With Silicon Bronze, due to its
shrink characteristics, the multiple riser setup is necessary to
avoid cracks at the web/rim junctions and also to avoid shrink
areas on the rim interior surfaces.

7-27-94
Winston Harness
73754,3177