Re: Gunmetal

"Mike H" <newsreader@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:o4kuXqGbT9IEFwdg@xxxxxxxxxxxxxxxxxxxxxxxxxx

I don't pretend any expertise but I have always assumed that even if
phosphor-bronze and gunmetal are not physically identical they are
broadly interchangeable insofar as model engineer usage is concerned.

Well that's far from my experience, the gun metal used in castings from
typical suppliers to this hobby is very different in machining properties
from the phosphor bronze bar supplied by same. Try tapping a PB piston
compared with the GM cylinder it's intended for, the former is a nightmare
the latter a piece of cake. Also the difference in these materials is the
reason PB is often used for pistons that run in a GM cylinder, they are
dissimilar materials so form a fair bearing, if they were the same the
piston would be supplied as a GM casting not as a more expensive piece of PB
bar stock.

Anyway that's my experience, but a quick google shows that a typical GM is a
88-10-2 (copper-tin-zinc) alloy and PB is similar BUT the zinc is replaced
by phosphor.

Greg


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