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  1. #21
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    I spent a few years working in a window factory where we had 5 CNC glass cutting tables processing 10's of thousands of square feet of glass a day. Anything from 2.2 mm up to 8mm thick. I won't claim to be an expert but I did pick up a few broad points. The main one being the cutter wheel 'blade angle'. I don't recall the relationship exactly but I know the thicker or thinner the glass you're cutting the more or less 'blade angle' you will want on your wheel. Pressure is also fairly critical - too much will flake around the cut and too little won't provide enough of a stress riser. As mentioned before, keep it lubricated and break it out as soon as you cut it.
    Glass cutting and breaking out is very much an art. It is very impressive to see a veteran 'glass cutter' at work - they make it look effortless. But if you're a rookie, you will be throwing away a LOT of glass.

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    Quote Originally Posted by JP Machining View Post
    Same principal works on flat glass though I have not tried it
    I need this toy

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    My dad and I worked in the glass industry for MANY years an I learned a lot from him traveling the world installing and teaching folks to run tempering furnaces,

    To address your question; Answer is simple you need to get a glass cutter with a carbide wheel and oil reservoir in the handle. I had mine for twenty years never changed the wheel and cut thousands of feet with it. Any stained glass supply will have one.
    1) Keep your tip clean (good advise all around).
    2) Firm pressure.
    3) Never run your cutter over a previously put down score line.
    4) Kerosene will work but I find it to thin and it stinks literally.
    5) Once scored just place the score line over the table edge and sharply snap down. For longer cuts place a wooden or 1/4" metal dowel under the line press down equally on both sides.

    Good luck

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    Quote Originally Posted by magneticanomaly View Post
    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...
    Nice project. The hand held glass cutters I have used would cut mirrors with over a quarter inch thick. I used kerosene because the glass would not emit much glass flakes. It gives a much cleaner cut and the break is easier.

    I never sharpened my cutters nor did I even mostly use kerosene because of speed. It the cutter did good I would not spend the time. You should take your time and use kerosene.

    I used my hand and feel mostly for breaking and sometimes used both if I had a piece of glass say 4 foot long cutting glass or mirror to size and square. Putting something underneath to break will break more than along the cut only as you likely are wondering about.

    Your handheld glass cutter if hopefully is a Pittsburg brand has keys on it to slip onto three different thicknesses of glass and you leverage the glass to break with. We also had a flattened set of glass pliers to break off very thin pieces 1/4 up to 1. Inch. Too occasionally I did use a tri pliers designed to help break a mirror cut which means also that with equal pressure top and bottom can help a lot if you take care.

    Like machining buy the best cutters that you can because if you have a bad cut then there will likely be a bad break. The idea of placing a pencil under the glass is possible yet very rarely used as you must lift the whole plate of glass up.

    It likes to break that way use a flat table nice non shag carpet can allow a very nice surface to slide the glass around. You must get the glass to overhang the edge of the table so you can hold the glass after good cut to break.

    What sizes of glass do you start with and what size do you cut to? Buy a new glass cutter or two they are diamond coated rollers. Never use one and expect it to work well if you do not know it’s history. I would never just use one that you gave me for example-nothing probably wrong with yours but I will not waste good glass on a questionable cutter.

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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.
    Yes it does flow over time.

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    Quote Originally Posted by michiganbuck View Post
    And the glass is faily new ..i tried cutting some old glass an is did noy cut well at all
    That’s because you never mixed iodine into your kerosene. If you had done that you could cut those cuts right just using a pencil. (Joking you)

    I am not a doctor though.

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    Doug,

    My understanding of tempered glass is that it is heated and then the surface rapidly cooled so it becomes essentially solid, then the inner portion cools and shrinks, putting the skin under compresssive stress. If glass flowed significantly during our lifetimes, the stress would fade and it would be back to ordinary glass.

    Is that correct?

    Bill

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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)
    On the car show with the two Brits uhh,. uhh, Wheeler Dealers, they had an episode where they needed a windshield and went to a guy in CA to have a 'custom' one made

    matched the arc then scribed and set it on fire.........fascinating

    Saab 96 episode, just looked it up

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    The factory wheels have a shape that is optimised. They don't actually score the glass but make a line of micro-fractures.

    The wheel should be in good shape.

    Kerosene or similar is a must.

    The "cut" should be done in one smooth steady pull.

    A dowel under the score line makes snapping the glass easier. As someone mentioned each split should be done immediately after scoring.

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    Quote Originally Posted by gustafson View Post
    On the car show with the two Brits uhh,. uhh, Wheeler Dealers, they had an episode where they needed a windshield and went to a guy in CA to have a 'custom' one made

    matched the arc then scribed and set it on fire.........fascinating

    Saab 96 episode, just looked it up
    The fire is needed on auto glass because of the laminated glass/plastic/glass construction.

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    On the 'can't cut old glass' thing -- I concur. I saved bunches of old window glass because I liked how wavy it was, and had multiple 100 year old windows that needed repairs. Could never cut the old stuff successfully, though. Gave up and went store-bought...

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    For those with glass experience, I wonder if the same general rules apply to heavy plate glass? I ask because I recently got a 12mm or 1/2" thick plate glass tabletop, for those times when I need something "mostly flat" but not "surface plate perfect". I refuse to allow abrasives near my granite.

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    Here is an article that probably tells you more than you want to know about glass aging.

    The polymer–polymorphoid nature of glass aging process - ScienceDirect

    One interesting comment was the time for complete relaxation of stress at room temperature.

    "The calculated extrapolated time of structural relaxation at the ambient temperature (about 293 K) amounts from 10*25 to 10*52 years."

    Longer than the present universe.

    Bill

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    I did a bit of research because I wanted to add a glass cutter to my CNC machine to cut shapes. I found this site (I have no relation to them), they have excellent tech manuals you can download.

    Technical Guides - MacInnes Tool

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    Quote Originally Posted by Trueturning View Post
    Yes it does flow over time.
    Over geological eras, maybe. Not in human lifetimes, or even the length of recorded human history. Glass is an amorphous solid. That means it counts as liquid for some technical reasons. But it is solid at room temperature, and it creeps less than steel at room temperature!

    You don't expect steel objects left lying around for 400 years to become Salvador Dali melted looking blobs, do you? Then you should not expect glass to do it either.

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    Thak you all for the great education!

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    Quote Originally Posted by pavt View Post
    For those with glass experience, I wonder if the same general rules apply to heavy plate glass? I ask because I recently got a 12mm or 1/2" thick plate glass tabletop, for those times when I need something "mostly flat" but not "surface plate perfect". I refuse to allow abrasives near my granite.
    i too have a piece of thick glass that refuses to be cut. i wanted to make smaller pieces for sanding/lapping.
    Last edited by dian; 05-10-2020 at 05:06 AM.

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    Bill:
    As far as your description of tempering goes; absolutely correct.
    When my uncle (owner of Hordis Bros. Glass in the late 70's) started developing the first (to my knowledge) continuous horizontal tempering furnace we quickly found tempering is a lot of science and healthy dose of art. Up till then glass was hung from tongs and run through a vertical furnace then air quenched. With the horizontal process, smaller and irregular shapes where now able to be run easier and cycle times could be decreased. The quenching process was changed some too.
    As far as glass "healing": I have heard that if you scored a piece of glass gave it enough time, came back and tried break it along the score line you would at best achieve mixed results. Tempered glass is a different story once heated and properly quenched the crystalline structure is permanently changed. As you correctly stated the surface is now under a lot uniform tension. This is why you can hit the surface with great force and it will not break, but look at the edge side ways and it will pop into a 1000 little pieces.
    There are a myriad ways to look at how the forces are distributed, but using polarized film is quick and dirty. If you have ever been driving wearing polarized sun glasses you have more then likely seen dark spots on rear glass of passing cars these spots are where the quench air has hit the glass upon its exit from the furnace.
    To answer your question about glass loosing its temper over time, this does not occur. Once that crystalline structure is set after the quench it doesn't re-arrange.
    I still am fascinated by glass it is such a unique material in a lot of ways. I never realized till after my fathers passing how highly regarded he was in the field. I still keep in touch with a few of his close friends in the industry. He taught me so much about the business, from running a tempering line to fixing large equipment.
    Thank for your interest just writing this brought back a lot of good memories (Thanks) if ya even want chat glass hit me up.
    I have read a lot of your contributions here and you seem to be like me in the respect of your never satisficed with just taking something at face value; you, like myself need to know why.

    BTW My father's first name was Bill.

    The verse is wild and supremely elegant place to have the privilege to exist if only for a nanosecond in respect to it's age. Not enough people take time just look at blade of grass or a flower, try it some time just 5 min. it might just change your out look, especially during these times.

    Regards,
    Doug

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    Quote Originally Posted by doug8cat View Post
    The verse is wild and supremely elegant place to have the privilege to exist if only for a nanosecond in respect to it's age. Not enough people take time just look at blade of grass or a flower, try it some time just 5 min. it might just change your out look, especially during these times.

    Regards,
    Doug
    Have you seen the clip where Richard Feynman is discussing a flower?

    YouTube

    Long ago I concluded that the main value of education, which is usually pitched for getting a higher paid job, is actually to improve your view of the universe for your own benefit. Do you want to look at a piece of limestone and just see a rock, or do you want to see the billions of sea creatures who lived and died over millenia, adding their microscopic contribution to the layer? One day, an artist friend who is a generally knowledgeable lady and I were driving under a highway bridge through a notch cut in limestone and she commented on the number of plankton, etc. who had made it. She not only looked at the surface, but mentally drilled down to the substructure, living in a brighter and much more varied world than many people have. As someone said, some people live their lives in default settings.

    Bill

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    Quote Originally Posted by 9100 View Post
    ... main value of education, which is usually pitched for getting a higher paid job, is actually to improve your view of the universe for your own benefit....
    Bill
    Oddly those two things tend to go together - 1) having an improved view of the universe, and 2) getting a better job.

    Higher paying or not.

    I got yelled at because I was late for 5th grade one morning. I was late because i discovered all these cool fossils in the front of the building stonework.
    Yep - limestone. Could not stop looking at them. Got yelled at. That teacher is gone, the fossils are still there.

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