Recently I've been noticing an odd warping in both wood and acrylic blanks. I will turn one side of the blank down, then go work on the other side, and when I go back to the first side, it's warped and makes my tools bump. I have a suspicion it may be my mandrel. It's had 3+ years of pretty constant use. Do I need to replace my mandrel, or is there a different issue? Thank you!