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darryl
08-01-2011, 12:09 AM
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?

macona
08-01-2011, 12:17 AM
A hot wire is probably going to be your best bet.

Heres is how to make one:

http://www.rhunt.f9.co.uk/Glass_Blowing/Hot_Wire_Tube_Cutter/Tube_Cutter_Page1.htm

darryl
08-01-2011, 12:58 AM
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?

claudev
08-01-2011, 01:01 AM
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).

macona
08-01-2011, 01:04 AM
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.

darryl
08-01-2011, 02:11 AM
Chip control- seems like a reasonable thing.

Got my tubing made into lengths anyway, so all is well. Thanks again.

DATo
08-01-2011, 03:12 AM
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.

Circlip
08-01-2011, 03:52 AM
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.

Leos
08-01-2011, 10:22 AM
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

gwilson
08-01-2011, 11:32 AM
True,glass needs to be broken instantly after being scored.

madwilliamflint
08-01-2011, 02:10 PM
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?

Evan
08-01-2011, 02:48 PM
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.

Cheeseking
08-01-2011, 03:04 PM
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.

madwilliamflint
08-01-2011, 03:35 PM
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.

garagemark
08-01-2011, 03:38 PM
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? :p

TexasTurnado
08-01-2011, 03:46 PM
According to a show on the Science Channel, glass is tchnically a liquid because it does not have a crystalline structure - they also claimed it will sag in time, so much so that vertical windows will get shorter. However, the time span was not mentioned - hopefully it is measured in millions of years or all the glass scales in DROs will soon be useless for precise measurents.... :D

DougC_582
08-01-2011, 03:56 PM
According to a show on the Science Channel, glass is tchnically a liquid because it does not have a crystalline structure - they also claimed it will sag in time, so much so that vertical windows will get shorter. However, the time span was not mentioned - hopefully it is measured in millions of years or all the glass scales in DROs will soon be useless for precise measurents.... :D
Glass is amorphous (a liquid) but the amount of time it would take to visibly change shape just from gravity alone is on the order of tens of thousands of years. The phenomenon hasn't ever been observed under atmospheric conditions.

Old windows were made of float glass. In that process the glass surface tends to end up at least a bit wavy, plus one end of the glass usually ended up thicker than the other. It was observed that the window panes were more durable with the thicker end downwards, so that was how they were mounted.

boslab
08-01-2011, 05:20 PM
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).
tis the standard lab method although we have carbide files for cutting these days, a tile cutter may help if your nervous, notch and stick in the mouth, self explanatory, you can fire polish the end.
regards
mark
[prisoner of the bos plant lab]

Evan
08-01-2011, 06:23 PM
According to a show on the Science Channel, glass is tchnically a liquid because it does not have a crystalline structure - they also claimed it will sag in time, so much so that vertical windows will get shorter


That was thought to be true but no longer. While glass does not undergo a phase transition as it cools it does undergo an energy transition. Depending on the chemical makeup at some temperature above standard temperature the energy level of the molecules drops below the temperature where those molecules are mobile. They become locked in place by atomic forces and cannot migrate from their fixed location. Even though glass is amorphous it is still technically a solid and not a liquid at room temperature. It does not sag or flow with time.

The presence or absence of crystal structure does not define the difference between liquid and solid. That difference is defined by the mobility of the molecules from which the material is made. If the molecules do not possess, on average, enough energy to overcome the energy "hump" required to move then the material is a solid. There are many examples of this, in particular glassy iron used to make transformers.

CCWKen
08-01-2011, 07:26 PM
Glassy Iron? Is that anything like transparent aluminum? :D

RPM22
08-01-2011, 07:41 PM
Trying not to derail the thread, but the OP already has his glass cut to size :-)

I have inherited off the street a piece of 3/8" plate glass about four feet square. It is extremely flat, so I'm guessing it's float glass, so I want to cut it up into smaller pieces , say 18" x 12", to use as flat surfaces for sanding. Any special techniques I should know about?
I already have a standard diamond glass cutter, cheap versions, and also a quantity of 'vanishing oil' which I believe is what the professional cutters use instead of spit ?

Thanks for any help in advance...

Richard in Los Angeles

Evan
08-01-2011, 08:03 PM
No, glassy iron isn't like transparent aluminum although transparent aluminum armor does exist. To be precise, aluminum oxynitride armor.

Glassy iron is made by spraying liquid iron on a chilled rotating drum where it cools so rapidly that there is no time for a crystal structure to form. It has very superior magnetic properties and transformers made with it have very high efficiency. It is used in power distribution transformers and saves a lot of energy.

To cut up your piece lay it on a flat surface (plywood is good) and using a wooden rule scribe a mark in one smooth stroke with the cutter. Don't try to scribe it twice. Use good force to ensure it makes a scratch and be absolutely sure that the scratch goes from edge to edge. A few practice runs on some scrap is advised. Once the scratch is made immediately slide the glass so the scratch just overhangs the edge of the cutting surface and break it by attempting to bend the glass down at the scratch. It works best if you grip the glass near the scratch and try to twist off the piece. Make sure you have a good grip on the piece you are removing so it doesn't fall. It is much easier to do than it is to describe.

Another way to break it is to lift the glass with both hands, one on each side of the scratch and then apply an opposite twisting motion with each hand trying to make it snap upward by bending each side downward. You have no more than 10 to 15 seconds to snap it cleanly.

Wear safety glasses.