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  • working with glass tubing

    I have some small diameter glass tubing which I'd like to use in a project. This stuff is about 1/8 inch in diameter, and I need to make several 1 inch long pieces from it. The ends don't have to be perfect, just reasonably square, and the length doesn't have to be perfect either. Actually, I need two lengths, one group about 1/4 inch longer than the other.

    Think of the glass in a fuse, basically that's about what I'm after, except the diameter of this stuff is about half that of a fuse. An F fuse would work, except it's not long enough, and I'm not going to destroy a bunch of fuses to maybe get enough for the project.

    I can't use a glass cutter because the tube is so thin. The best results I've had so far is grinding a line around it using the corner of a green wheel. I barely get around once and it comes apart in my hands. That's fine, but mostly I'm getting a chunk coming off as well, leaving the ends jagged. I can carefully grind the ends to get rid of the flaw, but often another piece will break out again.

    What else can I try?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    A hot wire is probably going to be your best bet.

    Heres is how to make one:

    http://www.rhunt.f9.co.uk/Glass_Blow...tter_Page1.htm

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    • #3
      Thanks for the link, Macona. Very interesting reading.

      I'm curious about the scribing knife. Is that anything special, aside from the shape? Seems to produce a good result.

      I went back into the shop to try grinding the mark again. This time I tried the other edge of my green wheel, which turns out to be closer to true. I used the lightest touch I could and went around only once. This time the tubing snapped cleanly, and I touched it up on the green wheel, again using the lightest touch I could. I made a few pieces to see if I could get consistent results, and it's looking quite acceptable now.

      Curious about another thing- why moisten the scribed line?
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #4
        Glass Tubing

        Nick the tube lightly with a triangle file where you want it broken, hold in fingers with thumbs opposite nick, and snap. Very easy to do. Have done a lot this way. (Standard technique when I worked in a lab many years ago.) To finish ends just hold in a gas flame (propane torch) until edges fuse smoothly. Glass is easily bent by hearing area of desired bend until it softens and gently bending it.

        CAUTION: DO NOT TOUCH HOT GLASS. IT WILL WELD TO YOUR SKIN.

        If you are nervous wear light gloves (but I never did).

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        • #5
          I usually just use a triangular file to score and then snap it. Usually just a score on one side. Hold the tube with both hands, score in front of you with your thumbs pushing against the tubing at the score.

          Some people wet it. I don't really get what that is supposed to do. Maybe stop chips from flying. Not sure.

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          • #6
            Chip control- seems like a reasonable thing.

            Got my tubing made into lengths anyway, so all is well. Thanks again.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #7
              Set up a base of some sort with a slot in it. Either machine a slot in a piece of wood or aluminum or make one using two pieces of material. Then set up a small (palm grip) air grinder such that a mounted thin abrasive wheel is vertical in the slot ... the thinner the better. Then just push the glass tubing through the abrasive wheel as you would crosscut a piece of wood in a table saw. If it leaves a chip sticking out at the end you can wet-sand it off using wet or dry paper.

              EDIT:
              Best if you cover the body of the air grinder by putting it in a small plastic bag with only the wheel outboard and having someone else spray it with water from a pump sprayer such as the kind that countertop soap comes in while you are cutting but I think for these small pieces you can probably cut them dry.

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              • #8
                Method used by Toy Train (Loco) makers is to nick glass with a triangular file and then, most importantly apply spit to marking and then snap at groove - - I don't know, but it seems to work.

                Regards Ian.
                You might not like what I say,but that doesn't mean I'm wrong.

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                • #9
                  Also important when 'nicking' glass for the break - either for sheet goods or tubular - is to not waste any time. break, snap, before the stress settles in - so to speak.

                  Leo

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                  • #10
                    True,glass needs to be broken instantly after being scored.

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                    • #11
                      Wha?

                      Originally posted by gwilson
                      True,glass needs to be broken instantly after being scored.
                      Ok, I'm not arguing, as I've perfectly zero knowledge about this. But why would this be true?
                      ----
                      Proud machining permanoob since September 2010

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                      • #12
                        I explained the mechanism in a previous thread. This is it:

                        When the glass is scribed the molecules in the scratch are brought to a much higher energy level which changes the elastic properties of the glass. At room temperature glass is considered to be a perfectly elastic material. That means that if it is deformed below the elastic limit it will return 100% to its previous shape and that is exactly what glass does. When it is scratched the molecules elastic limit is lowered for a short while because of the energy added to the immediate vicinity of the scratch. Because the material is amorphous it doesn't transfer that energy to neighbouring molecules nearly as quickly as a crystal structure does. That is why glass is an excellent insulator.

                        Because of the extra energy the molecules take much less energy to exceed the elastic limit so when the glass is stressed the limit is exceeded along the path of the scratch. Within a short period that extra energy is dissipated among the surrounding material and the glass is "healed". It will no longer break along the scratch in preference to anywhere else.
                        Free software for calculating bolt circles and similar: Click Here

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                        • #13
                          Interesting. I never thought about it that way but it makes sense. I was always under the assumption the scratch acted as a stress raiser (although your explanation clearly based on elevated stresses) but from the geometric standpoint of the crevasse area of the scratch being infinite small.

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                          • #14
                            Originally posted by Evan
                            I explained the mechanism in a previous thread.
                            Sorry. Must not have seen it.
                            This is it:

                            When the glass is scribed the molecules in the scratch are brought to a much higher energy level which changes the elastic properties of the glass. At room temperature glass is considered to be a perfectly elastic material. That means that if it is deformed below the elastic limit it will return 100% to its previous shape and that is exactly what glass does. When it is scratched the molecules elastic limit is lowered for a short while because of the energy added to the immediate vicinity of the scratch. Because the material is amorphous it doesn't transfer that energy to neighbouring molecules nearly as quickly as a crystal structure does. That is why glass is an excellent insulator.

                            Because of the extra energy the molecules take much less energy to exceed the elastic limit so when the glass is stressed the limit is exceeded along the path of the scratch. Within a short period that extra energy is dissipated among the surrounding material and the glass is "healed". It will no longer break along the scratch in preference to anywhere else.
                            OMG THAT'S TOO COOL!

                            Yes I'm 12.
                            ----
                            Proud machining permanoob since September 2010

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                            • #15
                              My wife is a professional framer. She will attest to the fact that you gotta get with it after the score. The scientific explanation by Evan is interesting, and I wasn't sure why it was, but I messed up several pieces of glass (cutting for her) until she told me I was just too damn slow.

                              Wonder what she meant?

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