plastics

Forgive me for raising a question which is not specifically related to CAD
or CAM but I have a problem which is perplexing me and preventing me from
finishing my mill !! ;o)

I have been making a new mouthpiece for my euphonium out of acrylic
(perspex, lucite?) and I have turned it from a solid 2" diameter rod. When I
finished it and polished it it looked the bees knees and I was delighted
but, since I have been playing on it for a few days, it has developed a
network of fine cracks around the narrowest portion of the bore. I am
assuming that these must be due to vibration from the sweet musical notes
but, since such plastic mouthpieces are made and sold commercially in the
US, I assume that they shouldn't be there and are probably due to stresses
already in the plastic.
Does anyone know if there is a way to stress relieve plastics after
machining?

Ian
--
Ian W. Wright
Sheffield UK
www.iw63.freeserve.co.uk