I just did a quick search on Google for stuff relating to this.

Here's a good description of the expansion formula for the brass plate.
The formula for the pin should be similar, shrinking in diameter
according to temperature.  Brass has almost double the expansion ratio,
so you will get more "bang for your buck" by heating the brass than you
will from cooling the pin.  Doing both would be best, depending on
diameter, you may get a really great lock.

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thexp2.html

This also has a table for the expansion coefficients.


>From my machinist's background, I have the following suggestions.

1) When drilling the hole, drill smaller than required and follow-up
with a "straight reamer" to get the hole size accurate.  Drills are
notorious for making slightly oversize holes from indicated size.  This
could be caused by chips, the flutes, whatever.  Use a reamer to get the
size exact, try for 0.003" undersize of the pin to start (depending on
diameter).

2) Slightly countersink the back side of the plate before insertion of
the pin, then after insertion, peen a little mushroom to keep the pin
locked.

3) Use no oil or lubricant!!  Without this, you may get an excellent
friction weld on the metals as the co-mingle during the transition back
to room temperature.

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