Harry tells it like it is. I picked up a nice chunk of "bronze" at one of my
favorite junk metal sites. A piece about 1-1/2 inch diameter and a foot or so
long. Figured great stuff to turn up the big bushing for the steam dome on
my Tich. Found I can not begin to cut it with HSS tools. Harder than the
hinges of that low place we all heard about. Makes a good hammer to whop the
end
of a push rod to loosen stuck morse tapers though.
Copper is a horror to try to machine. Wants to tear, gum up, and cutting
good threads is almost a forming operation, not a cutting process.
Harry again hit the nail as there are long lists of copper based alloys and
some with common names such as "Architectural Bronze" are not bronze at all,
just a brass of the attractive color used for good looking metal trim on
items. The old British articles speak of "Gun Metal" which I think is similar
to
what was called "five and three fives" alloy or in some places "ounce metal"
which was copper with the mix of copper, five percent each of tin, zinc and
lead. Ounce Metal was similar made by melting up a pound of copper and adding
one ounce each of the tin, zinc and lead. Most of the lead burns off during
melting, but enough remains to give nice machining properties.
Maybe not a big disaster except to your model if a fitting blows out during
operation, but I also build larger, ride behind models in 3.5 inch gauge and
with those there is some very delicate parts of my anatomy riding along
awfully close to that pressure vessel.
John Meacham
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