Instructables

How do I cut glass tubes?

So, I have some glass tubing, about 5mm diameter, about 1mm walls. I need to cut them to length for an Instructable (the cutting isn't the project, the tubes are raw materials).

How do I do it? I'd rather not heat them up as I want them to stay straight and cylindrical.

phunka4 years ago
Would these methods apply for a 6'' glass tube? and which would be best?
Kiteman (author)  phunka4 years ago
Six inches thick glass tube?!?

I'd guess you'll need a diamond saw??


phunka Kiteman4 years ago
Oh sorry 6'' in diameter. the glass its self isnt very thick. maybe 1/4''?
Kiteman (author)  phunka4 years ago
Er, I'd go with the saw, but make sure I had spare to practice with.

And goggles.
.  My guess is that he means 6" diameter, but, either way, I don't think scribe and snap will work well. I think you are right about using a diamond saw.
phunka4 years ago
I'd like to be able to do this at home, on the cheap. but also don't want to wreck this tube. It's 36'' as is, and I need to shorten it to 24-20''
callmeshane5 years ago

4 methods from professional / scientific glass blowers:

See website for neato pics:

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

Cutting Glass

Glass tubing and rod come in four (4) foot lengths and metric diameters. Four feet of tubing is rather awkward to handle in the flame so we need to cut it down to a manageable size. Select tubing of 10 mm OD and place on a flat surface. Mark the glass into 16 inch lengths.

Option #1

1. Create a scratch on the glass wall surface by drawing the corner of a file or tungsten carbide knife perpendicularly across the tube.

Tip: Do this step once creating a scratch approximately 1/8 inch long. Do not saw the glass. Sawing the glass will not make the process of breaking the glass any easier. It is not necessary to make a long scratch. A short, single sharp scratch is more likely to produce a clean even edge.

2. Pick up the glass tube and wet (water, saliva) the scratch with your finger. Turn the scratch away from your body.

3. Place your thumbs on the glass tube. The scratch should be located between the thumbs but on the opposite side of the tube.

4. Push your thumbs away from you. The glass tube should break cleanly at the scratch.

Option 2.

1. Hold glass tubing in one hand

2. Hold tungsten carbide knife in vertical position with other hand. Place glass tubing between your thumb and knife, hold firmly - horizontal and close to your body for support and stability.

3. Twist hand with knife - creating scratch.

4. Break tubing as in Option #1- step 4.

Option 3.

This option is useful on large tubing or when repairing vacuum lines or apparatus. This method should be tried after you have had some experience handling the torch.

1. Scratch tubing with file or carbide knife.

2. Wet scratch.

3. Heat the end of a 6 mm rod red hot - quickly place the end of the hot rod onto the wet scratch - be sure the scratch line extends beyond the contact area of the hot rod.

Tip: If done correctly you will observe a crack forming at and extending from the scratch. If the crack does not travel completely around the circumference: Tap the crack lightly. This action may chase the crack around the tube. Or, reheat the glass rod and reapply to the crack. Again, be sure the rod does not extend beyond the end of the crack.

Option 4. Access to a glass saw or cut-off wheel can make this process easier for some.
maker126 years ago
diamond tip cuter.
CameronSS6 years ago
NachoMahma has the method that you're supposed to teach to your chemistry students. Sounds like a good Instructable.
Linksies: We have the nice pictorial explanation from Teralab, plus other glassy instructions,
or you can get a specialized cutter.
Kiteman (author)  CameronSS6 years ago
Teach them to cut glass? I spend more time trying to stop it being broken! I've never had to make my own glassware, being more of a bucket chemist. I don't need to get a specialist cutter, as this will be a one-off 'ible, and absolutely nothing to do with chemistry.
Hmm...Our first lab of the year was over lab procedures, and the first part was to cut an 8" (that's 20 cm, Mr. Metric) piece of glass tubing, fire-polish the ends, and bend it 90 degrees (that's pi/2 radians, Mr. Metric...er, Mr. Radianic). We used 4mm tube, and the scribed line only had to go about an eighth of the way around. Teralab's explanation is exactly how we did it, and I got perfect breaks three out of three times. Now the bending, on the other hand, didn't become quite the pinnacle of perfection I was going for, but anyway....
Kiteman (author)  CameronSS6 years ago
The file-and-snap worked well - I have most of the pieces ready for final construction - and I found that I could also drill a hole in the side of the tube with the grinding bit of my rotary tool. The tube was thinner than I thought - the end had been "melted thicker", and it proved quite easy to grind off the occasional sharp corner (as long as I didn't get carried away).
Goodhart6 years ago
Yep, when cutting flat glass one simply scribes a single side, but since a tube's one side, is all the way around the outside, it may need to be inscribed all the way around (or maybe at least, 3/4 of the way around), as trebuchet suggests.
NachoMahma6 years ago
. Scribe the glass (rat-tail file works great). All you need is a good scratch on one side. Place the tubing on top of a pencil with the scribe up. Press. Fire the ends, if needed. . All safety rules for handling glass apply, so don't use your thumbs in place of the pencil, as I do. ;)
. Oops! Triangular file. Rat-tail is round.
Kiteman (author)  NachoMahma6 years ago
Thanks, Nacho. Time for a trip to the hardware store.
Just don't cut all the way through the glass (it will break badly) - just score all the way around... You should be able to snap it off as said :)
zachninme6 years ago
What? No fire involved? What about scoring, heating (not hot enough to bend, though), cooling, and repeating?
Bran6 years ago
Perhaps holding them under water and cutting them with a scissors might work. I'm not sure, as the tube may not be able to cut like sheets.
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