I'm thinking of
chucking the glass tube in the lathe, with the tube wrapped in a thin
sheet of rubber, and indicating it to center, then mounting the blade
in a dremel type tool on the toolpost, covering up everything involved
and using a water drip.


Hi Ken,

Your right on track. This is the best method to assure that your end is
square. Even better than a fancy glass saw! Just feed the saw blade in
slowly, don't force it through. You can cut a little faster at the start,
but slow up before you break through. You might want to slip a piece of wire
or wood dowel just inside the tube to catch the end as it pops off. You may
have a little chipping on the inside edge, but most of the surface of the
end will be OK.

If you use a heavy flow of water the blade will spray 360 degrees. You
might want to make a shield. A steady drip should be sufficient and help
keep the spray down. Just a long as you don't see the glass light up from
friction. If you don't use enough water it will burn the edge. This putts
stress in the glass causing it to crack.

If the blade is to coarse, you may have some saw marks on the ends form the
texture of the blade . This may be problem for a good seal if this is for
vacuum work. If this is the case, or if you have some minor chipping on the
edges you want to remove you can flat grind the ends. To do this it helps if
you put a slight chamfer on the outside edge using the side of the diamond
on the blade, or with sand paper or Emory cloth. To do the inside edge wrap
some Emory cloth around a dowel or anything round just to knock off the
sharp edge. This helps to keep the edges from grabbing and chipping out
more.

You can get piece of flat window glass to use as a lap table. (ask for some
scrap at the hardware store) To coarse grind the end down past the chipping
use about 150 grit silicon carbide grinding compound with water to make a
slurry. Use a figure 8 motion. Then use about a 320 grit as a finish lap.
Just make sure you clean everything thoroughly before using a finer grit
size. If this is for vacuum service go down another step to 600 grit. If you
don't have grinding compound try some wet sanding paper over the flat glass.






Thanks, Randy, for all the good info. I have a small diamond blade on
its way to me, and I will turn up a nice little arbor to hold it. I
am planning on water cooling while cutting. Should I go completely
around the circumference several times, deeper each time, or simply
cut straight down through the glass with the blade? I'm thinking of
chucking the glass tube in the lathe, with the tube wrapped in a thin
sheet of rubber, and indicating it to center, then mounting the blade
in a dremel type tool on the toolpost, covering up everything involved
and using a water drip. Does this sound feasible? Everything you
mentioned in the post seems to be "holding true", and I did even try
the hole in the block of wood method, but still no luck. I realize,
now, that I'm going to have to cut clear through the tubing to get
what I need, and then dress up the ends a little bit if necessary to
get them square and smooth. This stuff is a little nasty to work with
and to date I haven't had much luck with any of the methods I've
tried. The diamond wheel will be my last attempt, then I'm off to
someone that has equipment to do this job. Again, I appreciate the
info and help.
Ken.