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?