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    Default OT- Glass cutting

    I've been cutting glass to put into old factory windows that I am building into the house.

    Having fair success, using a cheap Fletcher steel-wheel cutter, with a wheel a little under 5/32" diameter. Dip it in kerosene for each cut. Usually. I can understand the kerosene lubricating that tiny axle, but it seems the lubed cuts part more easily, as if the kerosene does something to the glass. Invades microcracks?

    I want to learn more detals about the process. For instance, I have a nearly identical cutter with a wheel a little under 7/32", that will hardly score at all. I sharpened the wheel until it looks about as sharp as the other, still no good. I understand the larger wheel will not concentrate pressure as well, but they made it that way...What am I missing?

    Dies the process work simply by adding a stress-raiser, or does the crushing action leave residual compressive stress, or is something else going on?

    Would a scratch from a carbide scriber or diamond grinding-wheel dresser work better, or worse?

    I am sure somebody in this amazing brotherhood of skill and knowledge has investigated this...

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    One thing I learned years ago (and didn't believe at first) was that you have to break right after the score. You can't score a bunch of plates and go back and break later with predictable results, some how or other the glass begins to 'heal' or otherwise disseminate the stress right after scoring so the sooner the better.

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    Another thing that helps is to make sure the glass is clean. I had a dirty old pane lying around that I tried to cut several times and had bad cuts each time. After a good cleaning with windex, the cuts went perfectly, with all other conditions the same.

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    Quote Originally Posted by magneticanomaly View Post
    Would a scratch from a carbide scriber or diamond grinding-wheel dresser work better, or worse?
    They do make diamond tipped glass cutters, supposedly high end. I've always had good luck with the wheel type. After I bought our old
    house I was buying glass by the box load, so many windows were cracked. I think the key is practice a bunch. By the time I got done
    doing all the windows I was an ace. Not so much beforehand. It's not the tool so much as the hand behind the tool.

    1) be sure you have a solid surface to snap against. I tend to use a framing square, like up the score at the edge and one sharp snap.
    the glass can tell when you are tentative.

    2) +1 on being sure the glass is clean before you score.

    3) best chance for having a botched snap is when it's the last piece of glass in the box and you just need *one*more* piece to finish the job.

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    May not feel like it but glass is by definition a liquid. It does flow over time.

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    My first year Physics professor who I still see several times a year always maintained that if you wet the score line thoroughly with water before snapping it weakened the molecular bond and made a easier break. I have cut a fair amount of glass over the years and found that a good quality carbide cutter with a built in oil reservoir from a shop specializing in the stain glass hobby is worth the $30 or so investment if you are going to do any amount. Also there are special glass breaking Pliers for snapping the glass that are also worth having if you don't have a flat surface with a sharp edge to work with

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    Quote Originally Posted by magneticanomaly View Post
    Having fair success, using a cheap Fletcher steel-wheel cutter, with a wheel a little under 5/32" diameter. Dip it in kerosene for each cut. Usually. I can understand the kerosene lubricating that tiny axle, but it seems the lubed cuts part more easily, as if the kerosene does something to the glass. Invades microcracks?
    When one bends the glass, microcracks propagate from the scored line perpendicular to the glass surface plane. The kerosene or oil gets into the microcracks and prevents them from healing back to solid.

    I want to learn more details about the process. For instance, I have a nearly identical cutter with a wheel a little under 7/32", that will hardly score at all. I sharpened the wheel until it looks about as sharp as the other, still no good. I understand the larger wheel will not concentrate pressure as well, but they made it that way...What am I missing?
    No idea.

    Does the process work simply by adding a stress-raiser, or does the crushing action leave residual compressive stress, or is something else going on?
    The scriber or wheel puts a sharp edged scratch (a stress-riser) into the glass face, from which cracks propagate when the pane is bent.

    Would a scratch from a carbide scriber or diamond grinding-wheel dresser work better, or worse?
    If they are sharp. Traditional is a diamond point scriber, but I'd guess that a carbide scriber would also work.
    Last edited by Joe Gwinn; 05-08-2020 at 11:23 AM.

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    And the glass is faily new ..i tried cutting some old glass an is did noy cut well at all

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    Quote Originally Posted by Rickyb View Post
    May not feel like it but glass is by definition a liquid. It does flow over time.
    Not at normal temperatures. The myth about windows in Pompeii flowing down came because Roman glass making was not very consistent and many windows were installed with the thick side down. If glass flowed, we could not make tempered glass.

    I designed and helped build a lot of glass cutting machines to cut up Hematocrit capillary tubes. The controlling factor is the sharpness of the stress riser. It can be so faint that you can barely see it, as is done by a very sharp diamond. We used a carbide wheel about 1/2" in diameter sharpened from one side using a diamond wheel with its axis at right angle to the wheel's, making a hollow ground effect. We had drag on the wheel so it half rolled and half slid. They only worked when they were very sharp. A round bottomed score doesn't get it. The best cuts were from diamond scribers but they would not stay sharp long enough. We were making over a million capillaries a day and could not change cutters that often.

    I don't know about kerosene, but I know that water penetrates the glass structure and weakens it. The surface actually grows. We also made micropipettes from the same tubing by gauging the bore area and putting a mark on it. You could only use them once because the bore would swell and measure out a smaller quantity. The water doesn't dry out at room temperature, you have to bake it. Similarly, we made floats for specific gravity instruments from glass cane by holding the end in a flame and melting it back, rotating it to avoid the blob falling off. Surface tension pulls it into a sphere. They didn't actually float, but were suspended by a platinum wire on a balance with a counterweight. The glass blower had to make them slightly under weight. Then we would dunk them in water and weigh them to get the true operating weight, the gain being from adsorbed water.

    Be that as it may, the stained glass shop next door to mine is run by two brothers, one cutting and the other assembling. I know that they leave their cutters in kerosene. I can ask what brand of cutter, but I will have to call them because one has a wife with a severe immune deficiency and is in terror of bringing something home. They keep their door locked and will only talk to me by phone or through the door.

    Bill

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    Gordon said it, but I heard it a different way. "Get it while it's hot"!

    That is scribe and break in one operation,, the glass heals it's self if left to rest. the kero runs into the crack to slow the refusion.

    A good wheel, or a carbide/diamond works equally well for one who has mastered the tool will countless cuts.

    Clean glass , well oiled, breaks best. I like to use the ball end of the wheel cutter to "run the crack" on long breaks. Tap tap!

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    Modern hand glass cutters from Toyo or the like use a carbide wheel and the same is true for industrial machine cutters.
    A carbide scriber is much like a diamond to use for cutting glass- it works very well if correctly shaped but if the tip is too wide it ploughs into the glass and makes a wide scratch, damaging the edge of the cut glass. It takes a bit of time to learn compared to a carbide cutter but some of us are perverse like that.
    I use light oil on my cutters but it was traditional to use saliva after scoring, and certainly both of these result in a better cut.
    The glass flowing myth can be readily dismissed by anyone who has spent time working with old windows- it's common to have thickness variation in all directions.
    Is glass liquid or solid? provides some more on the physics of glass.
    Old glass can be difficult to work with because the annealing was very variable until relatively recently, and because the glass decomposes at some level where exposed to the elements. Some pieces will fly apart when scored or the crack will wander wildly, other pieces will be fine.

    Re tapping- yes it works, but have a look at the cut that results. It's much cleaner to run the cut with pliers or over the edge of the bench for straight work
    Last edited by Greenwud; 05-08-2020 at 01:07 AM.

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    Slight hijack.....how would I best cut sheets of two layer laminated windscreen glass?....Its old ,but NOS flat sheets ,stored in cardboard boxes (spares for army trucks)......would water jet cutting be applicable?.....I imagine it was cut with diamond saws,back in the day when this stuff was made(60s)

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    Quote Originally Posted by john.k View Post
    how would I best cut sheets of two layer laminated windscreen glass?
    It would depend on whether it is tempered or not. If it is tempered you will not be able to cut it. If it is not tempered a water jet should do a good job. I have had disks cut from 1/2 plate glass with a water jet and the results were very good

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    Quote Originally Posted by john.k View Post
    Slight hijack.....how would I best cut sheets of two layer laminated windscreen glass?....Its old ,but NOS flat sheets ,stored in cardboard boxes (spares for army trucks)......would water jet cutting be applicable?.....I imagine it was cut with diamond saws,back in the day when this stuff was made(60s)

    I know how to cut "tempered glass" into about 100,000 pieces in about 6 seconds........

    Use a cut wheel mounted on a side grinder ;-)

    seriously, a wet tile saw can work. It all "depends".

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    Quote Originally Posted by Greenwud View Post
    Modern hand glass cutters from Toyo or the like use a carbide wheel and the same is true for industrial machine cutters.
    A carbide scriber is much like a diamond to use for cutting glass- it works very well if correctly shaped but if the tip is too wide it ploughs into the glass and makes a wide scratch, damaging the edge of the cut glass. It takes a bit of time to learn compared to a carbide cutter but some of use are perverse like that.
    I use light oil on my cutters but it was traditional to use saliva after scoring, and certainly both of these result in a better cut.
    The glass flowing myth can be readily dismissed by anyone who has spent time working with old windows- it's common to have thickness variation in all directions.
    Is glass liquid or solid? provides some more on the physics of glass.
    Old glass can be difficult to work with because the annealing was very variable until relatively recently, and because the glass decomposes at some level where exposed to the elements. Some pieces will fly apart when scored or the crack will wander wildly, other pieces will be fine.

    Re tapping- yes it works, but have a look at the cut that results. It's much cleaner to run the cut with pliers or over the edge of the bench for straight work
    Accurately, Window glass is an amorphous solid. Akin to water ice. It gives under stress, and fractures when limits are exceeded.

    Gravity alone is not much stress for soda lime.....

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    Glass can be considered liquid because it does not undergo a phase change at a discreet temperature with a latent heat of transformation value. Most materials that can exist as a solid liquid or gas change between state at a discreet temperature with added energy input . For example water at 0 degree C can exist as either a solid or liquid and the difference between the two is known as the latent heat of transformation. As energy is input to ice its temperature rises until zero it continues to absorb energy but it remains at zero until it as absorbed the latent heat and then it becomes water at 0. inputting more energy will then raise the temperature of the water . Glass gradually goes from liquid to a taffy consistency to a solid over a wide range of temperature. Because there is no set phase change which defines the change from liquid to solid like most other materials it is considered to be a Liquid . That being said, it does not mean that class will flow over time at normal atmospheric temperatures

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    Same principal works on flat glass though I have not tried it

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    A wire wraped around and heated by electrical resistance works too

    as does filling a bottle with water or oil up to the parting line, and then playing a flame on the transition....CRACK! the part is done!..

    Kids games...

    Technical glass work is thrilling ...

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    Quote Originally Posted by john.k View Post
    Slight hijack.....how would I best cut sheets of two layer laminated windscreen glass?....Its old ,but NOS flat sheets ,stored in cardboard boxes (spares for army trucks)......would water jet cutting be applicable?.....I imagine it was cut with diamond saws,back in the day when this stuff was made(60s)
    Laminated glass can be cut by scoring and gently bending to crack the top layer, then turning over and scoring along the same line. The plastic interlayer can then be cut with a razor blade and gentle bending; I was taught to lay a line of methylated spirit along the cut line and light it to soften the plastic before using the razor blade but it's not aways required and recent H&S BS frown on the practice.
    Waterjet also works if you have complex shapes to cut.

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    [QUOTE=9100;3544620] The myth about windows in Pompeii flowing down came because Roman glass making was not very consistent and many windows were installed with the thick side down.

    +1

    I worked with a very smart ceramist and her comment was exactly the same. "you'd put the thick end down, right?"
    Window glass does not flow such that you can measure it. She did have some interesting comments about the windows
    in the Hancock Tower building however.


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