When we have an interference fit on two round machined parts, the trick is to heat the part with the hole and cool the part going in. The problem is that we never know when the hole is hot enough. Many perfectly machined parts have been destroyed by trying to assemble to soon or over heating. Here is the solution: Take a telescoping gage (snap gage) and set it with a micrometer to the desired hole size before you begin heating the part with the hole in it. As the heating process progresses, start checking to see if the snap gage will easily rock thru the bore. When it does, you are ready to install the other part in the bore. I have found that standard hot plates do an adequate job on small parts providing heat up to about 350°. (John Younger)

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