You sure did get a lot of tips most are right,.... sorta. Being that your
cutting Pyrex, (Cornings brand name for a 33 expansion borosilicate glass),
( AKA, Kimax from Kimble, & Duran from Schott), (and most recently, Simax
and Cinex from ......you guessed it,.... China) These and Quartz glass are
considered a hard glass, meaning it takes alot of heat to soften it. They
also have a lower expansion rate. Things like Coke bottles or windows are a
soft glass. Actually there are about 50,000 formulas of glass on file at
Corning. Each and every glass has it's own working characteristics and
compatibilities. They can differ greatly with their coefficients of
This is what makes the difference when trying to cut the glass with thermal
shock techniques. A string with lighter fluid will work on a coke bottle,
but it won't touch Pyrex. Scratching with a glass knife and putting a hot
rod on it will work as will using nicrom wire around it. However many things
come into play for different reasons and therefore these tricks are not good
for what you're trying to do. Basically because the piece your trying to cut
is so short. Also if the glass is not annealed will make a difference in the
outcome. Stress in the glass can make a crack run wild.
Because the piece is so short I am assuming that the ends need to be cut
square so to make a seal on the ends. There isn't much room for an o-ring or
compression fitting to work on the side walls.
The best way to get a square end that is not all chipped is with a diamond
wheel with about 220 grit or finer. Carborendom wheels will work good on
small diameter tubing , but not on large, the blade can drift and not cut
square. And always use water to cool the blade.
Tile saws will cut heavy wall tubes OK, but they will beat the hell out of
standard wall tubes. (a lot of chipping) Especially the ones with slots cut
in the blade.
Harbor Freight has a line of very cheap diamond wheels. But again they're
pretty rough for delicate cuts. They're better for ceramic tile and heavy
walls or chunks of glass.
The best blade I know of for your situation is one for Makita portable saws.
Makita offers two styles. One with slots in it and without. I have the one
without and it seems to make a pretty decent cut. It's about a 3 inch diam.
blade. Now if you only knew a good machinist that could turn up an arbor
shaft to adapt to Jacobs chuck on a drill or a flexible
Like cutting ceramic, you need to make a straight and steady cut. You cannot
bind or tweak the blade or it will break out the glass for sure. That's why
tile saws and glass saws usually have a carriage to hold the piece while you
If you still just want to scratch the glass to break it, use a piece of
tungsten carbide to make the scratch. Files are to coarse. You want to make
a deep, crisp, sharp scratch about 1/4 to 1/3 around the tube. Drill a hole
in a block of wood or 2x4 that is a snug fit on the tube. It should be just
deep enough so that the scratch is just above or flush with surface of the
block. Wet the scratch and pull back and away from the scratch. The wood
will give the leverage you can't get buy holding it. Using pliers you will
usually end up crushing the glass.
And if all else fails, Maybe I can refer you to someone in your area with a
glass saw. I have been a member of ASGS (American Scientific Glassblowers
Society) for 25 years.
SC Glass Tech.
Scam Diego, Comi-fornia