rounding over the sharp edge of a cut neon tube

Subject:	rounding over the sharp edge of a cut neon tube
Date:	Wed, 3 Feb 2010 01:46:51 -0600

hi,
wondering if i could ask a question, worried it's been asked many times
before, apologies if it has.
i got a few 4 foot long broken lengths of neon tube. i want to cut them
into approximately 16 inch long pieces and heat the cut ends to round over
and smooth off the sharp broken edges. i was told i could use a
("bernzomatic") propane torch to heat the glass enough so it melts (and
rounds over the sharp edge). i tried it and much to my surprise it worked.
i tried it on a few more pieces and i got erratic results. on some it
worked fine, on others it caused a crack to run down the length of the tube,
about 3 or 4 inches. this is what i don't want to happen. can anyone give
me tips or pointers on how to heat the end to round off the sharp edge
without causing the tubes to crack? i am so much hoping i'm not going to
need an annealing oven (cause i don't have one!).

b.w.