Martin Eastburn wrote in
:

On 8/12/2014 9:36 PM, Doug Miller wrote:
Martin Eastburn wrote in
news:PUzGv.194874$ne6.53439 @fx09.iad:

Heating the aluminum tube might expand it more than the
thickness of the metal. If so a hot tube might swallow a
dowel and cool skin tight.

No, it won't. Aluminum expands about 12 parts per million per
degree Fahrenheit. It would have to be heated to over 800
degrees F to increase the ID by just 1% -- and that's not
nearly enough to make the ID as large as the room-temperature
OD.

We won't even talk about what that would do to the wooden
dowel...


What type of expansion is that? Volume ?

No, linear expansion.

Try linear expansion. around the circle. It is a long ring. A
ring will expand more.

No, it will not. The diameter and the circumference increase by
exactly the same proportion.

Related thought experiment: suppose you have a string wrapped
tightly around the surface of the earth. How much longer does that
string need to be, if you want to put it on one-foot-high
standoffs all around the planet?

Think wagon wheel expanding the wheel band in a fire and then
sliding it onto the oak frame of the wheel. cool with water and
it fits tight.

I understand how that works. Do you understand that it's not *at
all* the same situation? Fitting a steel band over an oaken wagon
wheel requires only that the ID of the band is less than the OD of
the wheel at ambient temperature but greater than the OD of the
*wheel* when heated -- *not* that the ID of the band when heated
exceeds the OD of the *band* at ambient.

Do the calculations. Assume an aluminum tube with 0.875" OD,
0.050" walls, and therefore 0.775" ID, at 75 deg F. To what
temperature must the tube be heated to increase its ID to 0.875"?