Sciencemadness Discussion Board

Cutting a Test Tube / Glass Tubing

elementcollector1 - 27-11-2012 at 20:35

This isn't a chemistry-related project, but I thought I might bring it up.
What would be the best way to go about cutting the ends off of a test tube so that it's a fairly long, even tube? Would this be mechanical, or would dissolving in molten NaOH also work?
If a test tube fails, I might just order some glass tubing. If I do, how could I cut that (assuming it's a significantly longer tube than what I need)?

Lambda-Eyde - 27-11-2012 at 20:56

http://www.ilpi.com/glassblowing/tutorial_cutting.html

elementcollector1 - 27-11-2012 at 21:03

The problem with this is I usually want to cut the ends of a test tube off, so I can't exactly grab on to the end and snap. This will be useful if I end up ordering or buying glass tubing, though.

Lambda-Eyde - 27-11-2012 at 21:08

Sounds like method #3, #4 or #5 will do the trick, then. A Dremel with a diamond cut-off wheel could do the job.

watson.fawkes - 27-11-2012 at 21:30

For taking off an end like that, you can make a circumferential scratch with a file or glass cutting wheel. You'll need a jig to hold everything in place, but it's just a V-block to hold the test tube and a holder for the cutter. After you have the scratch, heat up the tube in a flame. The end will pop right off.

Standard lengths in glass tubing are 4 feet and 1.5 m.

Endimion17 - 28-11-2012 at 04:30

Huh, this can be a tough one. Try scoring it like watson.fawkes said, but wet the scored mark with water before applying flame directly up at the bottom. Water greatly increases the stress and is usually used when wider tubes are being cut.

If that fails, take a piece of resistive wire. Make a setup that will cause it to glow orange rather quickly.
Make a loop where you want to do the cutting (watch out not to create a short circuit), tighten it and then apply the current. It usually works. If it fails, score it, wet it, then tighten it in the resistive loop at the score mark.
This method works for cutting regular bottles.

If the cut is not even, you can carefully correct it with a sand paper, but then you must polish it with an oxidized flame and anneal in safety flame until you cover it with soot.

Sedit - 28-11-2012 at 19:45

Shock it.

Fill it with water to where you want to have it cut, freeze the water and drop it into boiling water. You should get a nice clean break right where the water level was.

You could also do the same with boiling water in the test tube and place it into ice water as well but I can't remember if I have ever cut borosilicate this way or not so GL.

This method provides a very clean cut BTW.

elementcollector1 - 28-11-2012 at 20:00

Quote: Originally posted by Sedit  
Shock it.

Fill it with water to where you want to have it cut, freeze the water and drop it into boiling water. You should get a nice clean break right where the water level was.

You could also do the same with boiling water in the test tube and place it into ice water as well but I can't remember if I have ever cut borosilicate this way or not so GL.

This method provides a very clean cut BTW.


That's an... interesting method! What does the broken-off part do, just sink to the bottom?

Sedit - 28-11-2012 at 23:34

Yeh just fractures at the point where the air and water meet. Its a glass cutting technique an artist friend of mine taught me and I have used it a few times.

sparkgap - 29-11-2012 at 01:34

Quote: Originally posted by Sedit  

Fill it with water to where you want to have it cut, freeze the water and drop it into boiling water. You should get a nice clean break right where the water level was.


Since water expands on freezing, I suppose one should make some allowances if a cut at a precise location is needed...

sparky (~_~)

Endimion17 - 29-11-2012 at 16:52

Quote: Originally posted by Sedit  
Shock it.

Fill it with water to where you want to have it cut, freeze the water and drop it into boiling water. You should get a nice clean break right where the water level was.

You could also do the same with boiling water in the test tube and place it into ice water as well but I can't remember if I have ever cut borosilicate this way or not so GL.

This method provides a very clean cut BTW.


Huh, that means your test tubes are quite crappy, probably cheap sodium glass.
Borosilicate test tubes have to endure such shock without snapping.

Sedit - 29-11-2012 at 17:13

Quote: Originally posted by Sedit  
Shock it.
can't remember if I have ever cut borosilicate this way or not so GL.


I have however done similar with Boro by making a circle score all the way around the tube, hitting it with a torch a the bottom and dipping that in water.

Just play with it you will see.