heat treating plastic

[William Sewell <cstmwrks@xyz.net>]

Hello,
         I have read bits here and there on heat treating plastic and
have a project that does not involve PVHO type standards and am
wondering if I could get some input. I understand that when dealing with
one inch thick plastic that it takes considerable time to heat up the
item, then it is held at 300 for two hours and cooled over several more
hours with fine control on the temp. would the time factor be the same
dealing with say 1/4" thick plastic as well? and after machine work /
drilling / heat forming it is once again heated but to a lesser temp...
one can only heat it so far and the plasic would loose its newly formed
shape, is this lesser second heating temp just below the softening temp
by as few a degrees as possible?

My thanks to any who respond.

Bill