Cutting a large-ish glass tube

[Jake of All Trades]

I have a piece of old labware that I need to cut in half (shorten), but I'm ashamed to say i don't know how!  It is a cylinder of about 3.5cm diameter, made of 1-2mm thick Pyrex glass.  I know how to cut small glass tubing (with a file), but how would I go about this?  I want the cut-off end to be as smooth and straight as possible, but I am only interested in one of the halves.  My dad does stained glass as a hobby, so I have all kinds of diamond cutters and a grinder at my disposal--but they are all for use on flat sheets...  Any ideas on how to work with a tube?

[rogue_designer]

last time I jury-rigged a sort of cardboard mitre box - with some corrugated and some rubber bands. That allowed me to spin the tube in a fixed depth (cardboard stopper at one end), and I cut track in the jib to hold a file in line - I just kept spinning the tube till the file broke through.

[CapnHarlock]

There used to be bottle-cutting kits available at craft-stores I haven't noticed them lately but they still may be available - basically a V-shaped base with a glass cutter wheel on 1 upper edge - You laid the bottle in the v-trough, rolled it around to score the glass, then tapped the inside with a tool that resembled a 1 ounce or so fishing weight on a wire.  I suspect you could duplicate the design with some scrap 1x3 and a hardware store glass-cutter. I don't know if this method would work on tempered Pyrex glass, however. I have never tried cutting Pyrex.

[Fantômas]

you can cut glass with scissors if you cut it underwater. The water dampens the resonance of the vibrations in the glass.
You still need to be careful and hotter water helps.

[Tinker]

Once long ago I needed a lot of glass tanks for an experiment, and I made them by cutting the tops off of gallon glass jugs (drank a lot of cider that summer).  I used a regular wheel glass cutter, and made a jig out of a pair of 2x4 scraps at right angles, such that the base of the bottle rested on one, and the glass cutter was clamped against the other.  Rotate the bottle against the cutter to get a good scribe line, then tap the scribe line FROM THE INSIDE OF THE GLASS.  That turned out to be the secret.  Broke a lot of bottles before I figured that part out.  I bent a piece of metal rod so that I could put it through the neck of the bottle and tap against the glass from the inside.  Just tap gently and rapidly against the scribe line, working your way around, and after a few taps, a crack will form and start following the tapping around.  Don't try to pull at the glass or force the crack, or it will wander instead of following the scribe.

Hope that helps a bit.

A.

[sidecar_jon]

All very good idea, i might add that i saw a guy cutting the tops off Carboys (Huge thick acid jars) but turning it ion an old record player turntable, with a fine flame playing on the line to be cut, followed by a wet wire. the thermal shock cracked it well. However as Pyrex is tempered im not sure that would work...on the net it seems recommended to scribe with a glass file and snap.


http://www.ecu.edu/glassblowing/gb.htm#cutting

[Smaggers]

I seem to remember something about filling the bottle to the point you want it cracked then plunging in a red hot poker.   It may have been parrafin rather than water, (don't try this at home kids).

[Ramiel]

Carefully with a dremel (or another rotary tool) with a diamond blade or a fiberglass blade, ALWAY wearing protective glasses (face shield), long sleeves and heavy gloves...
You should work very slowly and on a "dedicated" surface (a stand to hold the tube and a "guide" to keep the cutting edge straight).
Again, do it carefully and slowly...

BTW on the net you should find some specific tools for this purpose (glass saw)...

Just my 2c

[Gearly]

Here's a way to cut tubes and bottles that's been around for years (all safety caveats apply for Glass/Hot/Sharp work):

1. Make a score line where you want the glass to separate. I often use a triangular file to do this while the tube or bottle is laying on it's side. I usually rig a jig to help me make the scoreline perpendicular to the long axis.

2. Fill the bottle up with water to just under the scoreline (if a tube, stand it in a pail of water)

3. Wrap a length of copper or steel wire (16 AWG or similar thickness) around the scoreline just once and twist the ends of the wire together with pliers so the wire is really snug, and leave a 1" tail of twisted wire. The wire ususally needs to be readjusted so it is right on the score line. This step can be swapped with step 2 if it's easier.

4. A propane torch is used to heat up the twisted 'tail' of the wire until it is red-hot. Keep heating the wire for a minute or so.

5. Then, a stick or rod is inserted into the bottle or tube and on into the water, raising the water level.

6. When the water line hits the hot scoreline, the bottle or tube separates (ususally).

Works best with thinner-walled bottles and tubes (like food canning jar-thickness).

Gearly

[heresyoftruth]

There used to be bottle-cutting kits available at craft-stores I haven't noticed them lately but they still may be available.

I bought one of those for $30 a year or so ago, and it was an atrocious kit. I would have done better to buy a cheaper glass cutter and jury rig the rest, in my opinion. Perhaps I just got an especially cheap plastic kit by mistake.

[clockdug]

I hope you've fond a solution by now, but if not I would suggest contacting Ben Bowen through his website http://www.glassdomes.com/.  I used to be a member of a clock club in Tallahassee with him and can vouch that he is both very knowledgeable about such glass matters and a nice guy as well.  Hopefully

BTW, I'm not sure how well temperature based methods will work with Pyrex.  It's a boro-silicate glass which is very resistant to temperature changes.  That said, I have shattered a hot pyrex plate by running cold water on it in a fit of stupidity.  My wife is a lampwork glass artist; she's drooling to upgrade her torch set up so she can work with boro. 

Hopefully Ben can help!

clockdug

[Jake of All Trades]

There's a glassdomes.com??!?!?  ::Faints::  Prices seem reasonable too--thank you so much for turning me on to this! 

As for the tube cutting, I've still yet to get around to trying anything.  I've decided to go a different route on the project for which this was intended, but I still have a good-sized list of things to make with a cut glass tube...  I will let you all know how I got on whenever I do.

[apullin]

http://www.ecu.edu/glassblowing/gb.htm#cutting

Just score it and bent he tube, and it "should" break "cleanly" at that end. It hard to get it perfectly flat, especially for that size. Practice on some standard Pyrex tubes (easily available online).
Possibly packing the inside with sand first might help?

Then you can always fire-polish the end if you need to.