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Making the Cut

In the process of making neon, one of the most important procedures is the cutting and splicing of the glass tubing. There are many different techniques and various tools that can be used that I would like to discuss.

By Tom Cage

A good splice or weld is important to making neon because it has to be done in all neon units and can determine the quality and the beauty of the glass. As a beginner, this is usually the first thing learned, and unfortunately one of the first things forgotten. I strongly reinforce this when teaching a student by starting almost every practice session with at least 10 to 20 welds of straight glass to continually emphasize this.

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  • Cutting and splicing

    The majority of neon units have at least two electrodes and most often, more than four feet of glass, so there are at least three welds creating just as many chances for leaks and weak spots in the tube. The majority of the problems that slow down the bombing process are usually caused by a leak in one of these welds or the tubulation hookup to the manifold itself. Obviously, you can see that a good weld is also important to production efficiency.

    Probably the single most important aspect of splicing two pieces of glass tubing together is in the cutting of the tubing to achieve as close as possible a perfect match before joining together. Having two jagged, uneven pieces of tubing makes it extremely difficult to achieve a proper weld. Therefore, having many different cutting techniques is a must for all the different situations that may arise. Also, there are many different tools on the market that make these various techniques easier.

    The first and most common way of cutting the glass is with a file. There are many different types available, and the majority of glassblowers buy them from their local sign supply company. You usually take your chances here and it has been my experience that the suppliers really don't know what a good glass file is and rarely are you able to get the same type twice. There is an enormous number and type to choose from, so it's really a matter of personal taste as far as the size, length, and coarseness of the file, but be sure to get one that is "twice cut".

    The basic cut is made by laying the file on it's edge at a 45 degree angle and filing a groove in the glass and applying pressure to one or both sides of the tubing away from the groove in a quick snapping motion.

    “Easy enough” you say, and it really is as long as the glass is straight and hasn't been heated in the fire or is very close to an area that has been heated.

    Because this is the easiest and most effective way of cutting glass tubing, you should try to plan your welds to be in a straight piece of tubing if at all possible because this method almost always produces a good clean cut.

    Aligning for the weld

    Most glassblowers prefer to make their welds in a section of glass that is going to be hidden by block-out paint or behind the face of the neon so they are usually in sections that are raised up from the worktable. It is important that the two tubes are going to be in a straight line after the weld, so I recommend using some wood blocks of the proper height to align the tubes before welding.

    If you are welding powdered tubes together, it is best to take a cork and clean a thin rim of the powder out of the tube end so that it won't get into the weld and possibly cause a leak. As you get better at welding, this isn't always necessary, although I would definitely recommend it when using any of the blues or purple. For some reason these certain phosphorous' cause the weld to crack during or after cooling.

    Unfortunately, you can't always weld in a straight section of tubing. Many times it is required that a weld will be in a curved section of glass and usually exposed for everyone to see, and this can cause beginners a lot of grief. Whenever a curve is made with hot glass and laid on the workbench, the glass that touches the tabletop cools at a different rate than the rest of the tubing, therefore causing stress in the glass wall. When the glass is cooled off and the usual method of cutting with a file is tried, there is a 50/50 chance that the bottom side of the tube will start splitting along the tubes length, and when you try to cut the split out, it just keeps on splitting and splitting. Very frustrating.

    There are several different ways of alleviating this problem. I have found that the use of an electric glasscutter is the quickest and easiest way to get a good clean cut.

    This is a device that has a control base with a long chord attached to it and on the other end a hand held clamping device with a loop of nichrome wire to fit around the glass tubing and a push button to activate the current of electricity to the wire. This method of cutting the glass is done by clamping the wire around the tubing and pushing the button to start the electrical current flowing through the nichrome wire. This wire gets very hot quickly, and creates a uniformly stressed area around the tubing. After approximately 10 seconds, the wire is quickly removed and a small amount of moisture is applied directly where the wire was with a finger, and the tube will immediately crack along the stressed line where the wire was. This tube should be welded as soon as possible to eliminate the possibility of splitting when cooled. With a little practice and trial and error, you should be able to master this technique in no time.

    If you're unable to find or afford one of these type of glasscutter's, (they run over $100), there is another technique that works just as well and doesn't cost anything. This procedure uses either a hand torch or a 5-point crossfire with a very sharp tipped flame. Mark the glass where you want the cut and by using the flame of either of the fires, spin the glass around in the flame exactly on the tubes diameter where it is marked for approximately five to 10 seconds. Now let the glass cool for approximately 70% of the time that you held it in the fire. Gently place the glass file on the mark and lightly file until the glass cracks. This method will take a little more practice, but once you have mastered it, it is a very effective way of cutting curved glass.

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    Heating to cut

    Unfortunately neither of these methods is 100% foolproof, and so every once in a while you'll have a tube split down its length on you. All is not lost because there is a very effective way of "saving" this piece of glass. Have the other piece of tubing that was going to be welded to ready to go. Place the tube with the split lying on your workbench with the split facing up. Take the hand torch and slowly start heating the tube right on top at least 2" away from the split.

    Gradually start moving the torch toward the split until the glass is starting to melt and sealing the crack from the front side. Slowly continue sealing the split until it has completely returned to the end of the tube.

    Then, immediately weld the two pieces of glass together.

    This method takes a lot of patience and there is no guarantee that it will always work, but you haven't lost anything by trying. With practice you will get to where those splits aren't as much of an annoyance as they use to be.

    Classic glass

    Working with classic glass creates a whole new problem when it comes to cutting and splicing glass together. This type of glass is much harder and if you are unfortunate enough to be using the old hand drawn tubes, you know what I am talking about. Because the glass is so much harder, it dulls the glass file very quickly so it is best to have a grinder close at hand because a sharp file is a must. If you are going to be doing a lot of classic glass I recommend that you invest in a diamond file. They don't dull like a regular file and try to find one with the sharpest edge possible to make as small of a groove in the glass as possible.

    I have found that to get the best possible cut and the cleanest edge for welding, be very forceful with the glass when snapping a piece off. If you try to be too gentle with the classic glass you may end up breaking the glass in a bend or some other undesirable place. If you have made a good groove in the glass where you want it to break, give it a really hard and strong smack and it will break clean for you the majority of the time. One of the previously mentioned electric glasscutters is a must if you do a lot of this type of work.

    With the advent of the new Pyrex manifolds replacing the old lead glass type, it is necessary to periodically cut Pyrex tubing. Your usual glass file is worthless for this matter. A piece of tungsten carbide is what is used to score a line along the tube where you want to cut. For some reason, if you wet the line with your finger, this makes the cutting so much easier, but I wouldn't try this to close to a branch section of the manifold or you may break the whole thing. If you need to cut Pyrex in a very delicate or tight place, there is an easier and less nerve racking way.

    First use the tungsten carbide blade to score a line about 1/3 of the way around the tube and then wet it slightly. Then take a piece of tubulation glass and heat it to the point of melting. While this glass is still molten, quickly place it on the line scribed on the Pyrex tubing, and you should get a very clean cut. This also works very well on the classic colors too.

    The best way to eliminate the possibility of leaks in welds is to have as few welds as possible. A good glass blower should be able to bend a full stick of glass from end to end, no matter what the pattern style, but that requires knowing how to skip a lot of different varieties of bends, but we'll save that for another time.

    Tom Cage has been in the sign business since 1975. Mr. Cage is a consultant, writer and runs his own neon business, Neon Specialist, in Colorado Springs, Colorado. For more information you may visit his website at

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