Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Good luck.
  As for me, I use a small fine file (the sharp edge) to score the tube, all around, where you
want the break. I put my thumbs closely to the left and right of the score line and the rest
of my fingers to the other sides.  A deep breath and a quick snap movement and you are done. 
I always clean up the ends with silicon carbide paper - 320 works pretty well and allows you
to get the exact size needed.  Sand a bit, test the fit, sand a bit, test the fit is the idea.
In fact, I just used this technique for an Empire 30 sight glass.  I use doubled over and twisted
teflon tape as a sealer.  Other steamers use different methods with success.  Hopefully, you have
enough glass tubing to try again if it doesn't work well the first attempt.  Keep in mind that some
tubes sit exactly between the fittings and some are meant to go in a bit on both the lower and upper 
fittings. My Empire 30 was like that whereas a later version 43 has a sightglass that fits exactly
between the fittings.  Go figure.

  The file will dull a bit, but is worth it.  I've used the same 'marking' method many times
with the same file and I still find spots on the file that work.

Good Luck,
Wayne