[TheForge] shrink fit techniques

[theforge@mailman.qth.net]

Two things, 
One, you say dowel.  If the dowel is drill rod, you may be getting it hot 
enough that when you quench it you harden it.  That being the case, it will 
change size (austenite to untempered martensite), carbon steel grades will 
usually shrink, and the S types grow, although it usually grows much more in 
length than in diameter.
Two, try cooling the pin and not heating the hole.  The hole may be getting 
smaller from heating, then when you force the pin in it actually acts like a 
drift and enlarges the hole.
Michael