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Jeff Wisnia Jeff Wisnia is offline
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Default Badly behaving brass

dadiOH wrote:

I used to have a wooden sail boat that was made in the 30s. There
were several forged iron rings on various spars and I was told that
the way to get them on was to make the ring with a slightly smaller
inside dimension than the OD of the spar at th desird ring position,
grease the spar, heat the ring, position the ring on the spar and then
toss a bucket of water on it. The ring shrinks and is forever at the
correct place.

Well, lately I have been making myself a new cane. The shaft is
hickory, head mahogany. The shaft is reduced into a shouldered
spindle where it goes into the head. I wanted a transitional
pretty-pretty between the two different woods and decided to use
brass. A piece of 3/4" brass pipe is just the right outside diameter
but the inside diameter was a bit too small to get over the spindle so
I decided to try the heat & quench method ala spar rings.

I cut off a 5/8" wide piece of the pipe to use as my ferrule and
heated it up to see if it would expand enough to get over my spindle.
The dang thing didn't get any bigger; in fact, the ID *decreased*.
Huh? I thought about that for a moment and decided that the wall of
the brass ring must be expanding both outward and inward and therefore
the ID was decreasing, OD increasing.

But then I started thinking about what would happen if I cut the brass
ring and flattened it out into a strip. That strip would be 5/8"
wide, about 1/8" thick and 3+" long. Heat that and each dimension
should increase but the length would increase most, right? Bend that
now elongated piece of brass back into a ring and the ID should be
bigger, right? So why did my piece of pipe decrease in ID when I
heated it?

You are correct, everything I ever learned about thermal expansion says
that holes in metal things get larger when the thing is evenly heated.

What proved to you that the inside diameter really *decreased*?

How about just finding someone with a metal lathe and opening up the ID
of that bit of pipe to suit what it has to fit over?

If the piece of pipe is not veryy long, you could probably open up the
ID in a few minutes with a round or rat tail file. No one is going to
see what the ID looks like after your cane is assembled, are they?


Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.