Question regarding shrinking epoxy resin cap after turning

[KingShoe]

I'm a budding pen maker, about 25 bespoke pens in.  I've made countless pen kits but just started my bespoke journey.  All started out well, but recently I started a batch of 7 pens.  Two of the 7 have an issue where either the threads on the cap are shrinking, or the non-threaded part is swelling.  Result is a VERY noticeable "dip" just behind the threads.  Same resin, same technique, 2/7 have the issue.  I figured it's heat related so I've slowed way down on drilling and tapping making sure there is no heat build up.  I've let the caps sit overnight after drilling and tapping prior to shaping.  Just turned 2 more today and one of them is afflicted.  I am at wit's end...  Has anyone else run into this?  Lastly, I've heated the shrinking/swelling caps with a heat gun while on a mandrel back to the right size and then dipped them in ice water to try and set the corrected shape.  That hasn't been successful either. 

 

I'm using epoxy resin not Alumilite Slow since we had the better part of 2 gallons on hand.  I have since ordered Alumilite Slow thinking maybe being poly resin that would alleviate this situation.

 

I have 2 questions:

 

1.  What am I missing in the drilling, tapping, turning process that may be causing this and,

2.  Is there a sure fire way to reshape these caps?

 

Thank you in advance,

 

Adam