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Thread: Glass fabrications/cutting techniques: Post your questions here (and basic tut.)

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    Glass fabrications/cutting techniques: Post your questions here (and basic tut.)

    I figure I am getting a lot out of this board so I might as well contribute something if I can. I think glass is under utilised in DIY setups due to perceived difficulty or danger of fabricating glass when in reality it is very easy compared to cutting acrylic, especially with limited tools. Since I was small I have been helping my father build a niche manufacturing business called Hopf ground glass making speciality glass diffusers for large format cameras, which where each cut by hand to extremely close tolerances (.015"). I learned a thing or two about running a small business from the ordeal, but what I really learned to do is cut glass. I have also had a little bit of experience with acrylic fabrication and I know how challenging it can be to get a good cut even with good woodworking tools at your disposal, and then you have to deal with making the glue run correctly. I may be biased but I think glass is a very attractive option for anyone trying to fabricate a clear vessel such as a compact algae scrubber or aquarium.

    Cutting glass vs cutting acrylic:

    Acrylic is usually cut using similar techniques as for wood: saws, routers, mills, etc. Glass can be cut using abrasives (expensive, difficult) or by the "score and snap" method which works by scratching (scoring) a line in the glass to create a week areas where the glass will break (snap) easily.

    I have a very limited experience cutting acrylic with tools including razorblades and scoring tools, handsaws, table saws, band saws, routers, etc. for projects requiring varying degrees of finish and accuracy. Cutting acrylic seems attractive because it is similar enough to cutting wood or other conventional materials that it feels somewhat familiar, at least it is to me. Cutting acrylic pretty much requires power tools, or possibly score and snap with a lot of secondary work, if you want clean edges suitable for gluing. Cutting acrylic seems easy until you try it, and you realise that hand scraping each sheet for 2 hours to get good edges or spending 100 bucks on a special table saw blade sucks. A simple "Red Devil" glass cutter available at hardware stores everywhere for under $5 can do an excellent job on glass

    Cutting glass is scary because you only get one try and people are often afraid to break the glass. I will explain a very easy way to break a scored sheet of glass that will produce better results than almost any other method and with proper precautions makes it impossible to be cut when the glass breaks. I will also explain how to easily and accurately cut glass using no more than $20 worth of tools if you don't already have a steel ruler and some spring clamps. Glass is also significantly cheaper than acrylic so while you only get one chance for each cut, you can easily make dozens of practice cuts in an hour or so with practically no cost.

    Cutting glass is a two step process that is almost universal among glaziers. Very rare circumstances require other cutting methods. The standard method is the score and snap method using the red devil glass cutter. Simply measure out your dimmensions on the glass with your steel ruler and a fine point sharpie. Make the markings as accurate as possible because with some practice you should be able to go right through the center of that fine tip sharpie line every time. The next step is critical. The most diffucult part of cutting glass is holding down the straight edge. You need to line the straight edge up with the marks you made on the glass and use it to guide the glass cutter across the glass in a straight line, But you will be using one hand and to push hard against the fence (straight edge) while trying to hold it down with the other hand. This is often times what glaziers do when perfect results are not nessesary and 1/6" of slop is no big deal, but they have a very steady cutting hand and the average DIY'er will not have that at all. thankfully if you clamp the fence down to the table underneath the glass you are cutting it you will get very precise results easily. We generally would use a board a little wider than the length of the cut we wanted to make and clamped the fence down to the board on top of the glass. you might need to be creative depending on the size and shape of glass you want to cut, but like i said, this is the very hardest part. Fortunately, you will not have to go thrugh the painstaking process of lining up the fence with the marks every time you practice. What you really need to practice is the ability to apply even pressure throughout the cut without chipping the edges of the glass when you go over them. You will likely get small chips as a beginner, this is not really a big deal but it would not look great for a rimless tank.

    Once you have your fence clamped down you will need to score the glass with the carbide wheel of the cutting tool. There is a depression cast into the red devil cutter and most imposters near the cutter end. This depression has been out there for a reason and if you hold the cutter in your fist with your thumb in that depression your hand will naturally grip the cutter correctly. Hold the flat edge of the cutter against the straight edge with the wheel parralelll to the straight edge. The wheel should be touching the glass with the handle coming towards your body at about a 60 degree angle from the glass. This is the position you will hold the cutter in as you pull it across the sheet of glass along the fence to score the glass. It should be mentioned that WD40 or oil on the cutter will help the cut a little bit. What kind of oil you use makes no difference, it can be neatfoots oil for all the glass cares. put a drop of oil on a plate and roll the cutter through it before making each cut. Start facing parrallel to the fnece with the cutter against the fence on the opposite side of the glass, with the wheel right on the edge of the glass, if not going over the edge a tiny bit. Pull it across the glass applying firm pressure mostly downward and somewhat against the fence to prevent your cut from wandering. Continue the cut until it goes off the opposite edge. You are applying correct downward force and speed when the glass crackels as it cuts, kind of like cooking bacon. Pushing to hard will make the cut worse. To avoid chips on the edges do not push quite so hard for about 1/2mm at the start and end of the cuts. If in doubt, start with the cutter slighly over the edge of the glass and dont apply full pressure until the cutter is over the edge. Similarly, make the pressure lighter as soon as you feel the cutter go off the opposite edge.

    A note about glass safety:
    There is only ONE way to be cut by glass and it is very simple to avoid. The only way to be cut by glass is by touching the sharp edges. Never touch the sharp edges, and it is impossible to get cut. In practicality you will have to touch edges occaisonaly, like if you have to pick up a sheet of glass off the floor with no fingers. As long as your fingers are not moving along the edgeyou are also very unlikely to be cut. it is like shaving, the razor can only really cut you good if you move it sideways across your face. I can handle sharp sheets of glass 8hrs a day for months and never get cut, and even when I first started I rarely got cut. Maybe in my entire life 10 times or less have I been cut by glass while I was working with it. With that said I never dull the edges until they are ready to go into a customers hands, and then I only dull them as much as is required to keep them from cutting somebody, which is a few light strokes with 200 grit sandpaper. I recomend doing the same, at your own paril should something go wrong. Of course some people will be rather uptight about glass safely telling you you need to wear gloves, gogles, leather apron, bullet proof vest, pimple protector, etc, etc. I say never forget your towel and always have a pair of safely glasses on while breaking glass.

    Breaking the glass:
    Before you break the glass, spread liquid along the line on one side. Saliva works. The liquid being drawn in by capillary action actually wedges the glass apart and helps the cut. Your score line actually made a very small, precise crack all the way across one side of the glass, all you have to do now is apply a little pressure to the other side and it should break easily. Lay the glass on a carpeted floor with the scored side down and put your index finger tips precisely on the line from the opposite side of the glass. This is only hard with opaque glass. Space them equally from each other and the edges of the glass, deviding the line into thirds. Push down until the glass snaps cleaning in two peices along the line. While I have never been cut after using this technique tens of thousands of times, you may feel it nessesary to wear gloves for this parts, or even put a towel over the glass. The glass will not fly when broken unless except possibly in very very tiny shards which have been embeded in my eye before but cannot really hard you otherwise. The only time I would wear gloves is when breaking glass that is requiring a large amount of pressure to break. If you have to press really hard it is more likely the cut will not be clean and sometimes your hand will slip when the glass finally does break. You do not have to worry though, glass shards will actually very rarely cut you. We had a linolium floor that would be littered with glass scraps at time and I would never wear shoes and only got a splinter every couple of months while working constantly. The point is it is actually very hard to be cut by glass unless you do something really stupid, just be careful and dont worry about it.

    Sawing and drilling glass:

    Glass can be cut wet by abrasive diamond tools when an inside corner or through hole is required. Drilling tanks is a common example. Drilling glass is very easy with a core drill and a drill press. You can superglue another peice of glass to the other side with a lot of glue to prevent the glass from chipping on the exit of the drill, which works very well but requires several days of soaking in strong solvents to be removed, but otherwise you are going to ahve vhips ont he exit side and possibly the entry until you get a feel for it. With a hand drill all bets are off, a dremel with a diamond point might work better but you can use a core drill with a hand drill by starting it at a 45 degree angle to make a divot for the edge to run in and then slowly moveing it to 90 degrees as the drill starts cutting. This takes a lot of practice though so use some scrap. The same rules apply as with glass cutting: practice makes perfect, do a lot of practice holes before you try to drill something you cannot easily replace, like a curved glass surface. No matter what abrasive method you use it will need a lot of water on the contact zone. The common choices for sawing are the tile saw and ring saw. Bother are farely expensive and have water resevoirs to keep the blades wet. You can rent a tile saw at home depot for a reasonable rate, or so I hear, They also make diamond routers for glass which can be used similarly to how routers are used for acrylic. These are called edge grinders and are probably the most usefully diamond tool you could have for glass but they cost a couple hundred bucks.

    Gluing glass:
    Glass can be glued fairly easily using silicone, however this is its own tutorial and I am not the best person to write it. Personally I find glass much easier to glue than acrylic, though.

    This is obviously just the tip of the iceberge and I am currently pulling an all nighter between second shift and class at 8 am, so I am sure there may be some coherency issues which I will fix after I have had some sleep, but it gives you a general idea. Please ask as many questions as you can think of, I can probably answer them or at least help!
    Last edited by Pulse; 12-08-2012 at 03:37 PM.

  2. #2
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    Lots of great information, thanks!!

  3. #3

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    Floyd, I think you should consider using glass for the lenses on either side of your screen. Good (borosilicate) glass will be more clear than acrylic and more importantly it is 100% UV resistant and stronger than acrylic of the same thickness. I am not talking about regular window glass here, I am talking about the stuff used for pyrex, it looks like starphire but it is is clearer, cheaper than acrylic, and extremely strong. It is also very scratch resistant compared to regular glass.

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    My first trade was glass. I was not a glazier although I've done many a window. Too any to count. But you're right. Glass is easier to work with. Or was. Reflecting back 31 years. A belt sander is handy to knock off edges to save fingers. One shop I worked in we had sheets of glass bigger than garage doors. Used a crane with suction cups to hoist it to tilting tables. Used air to move it around once it was on the table. We also did tempering and beveling using large spinning wet stones by hand. Did I say by hand? Man I feel old.

    Pyrex and Corell are actually types of glass as well as they have become brand names. Both need to be molded. Can't cut either one with a tool. If you take the time and look at your mother or grandmas Corell dishes or cup on the brim or rim and/or your glass measuring cup(may see the seam of the mold). You can see the pour mark.

    Glass can also be all natural found in certain places around the world. Man has just refined it to what it is today. Black glass is more commonly found than any other color.

    I used to be into glass. Was sort of proud of being in that trade. Being a kid and knowing a trade was pretty cool then. Used to throw 48x84 sheets of double strength glass around like cardboard. Meaning flopping them on tables to be cut. I have a good wingspand. I've done sheets a as big as 60x108 by myself. Having a time warp moment here.

    Anyway. Thanks for the memories kid.

  5. #5

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    Cast sheets of borosilicate can absolutely be cut with a tool. Its not easy, but you can get pretty consistent results if you tap the back of the glass a lot then use a straight edge to snap it against a towel or carpeted bench. Pyrex has recently been turned into tempered soda lime glass but the originals where annealed borosilicate castings.

    To give you guys an idea of how quick it would be to cut these pieces, any decent glazier could cut out glass for a 55g tank and whet sand the edges perfectly in about 15 minutes. With a jig you could do it in 10 minutes or less. This is probably still the way most tanks are made.

    It looks like I will be doing a custom 180 square inch scrubber out of glass to be used as a display unit at a LFS in the next couple weeks. I will take plenty of pictures for a build thread so you guys can see how easy I make it look .

    Please pardon my spelling and grammar in the original post I promise I will make it perfect first thing tomorrow morning. I wouldn't have posted it if I realised how bad it was.

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