--Cradle of the Sun Tips

Glass Cutting - Soldering - Leading - Glass Creation/Selection - Tools Supplies/Equipment - Puttying - Misc

Glass Cutting:

The technique for cutting glass is very simple. The novice needs minimal practice to develop a feel for scoring and breaking out. However, it will help to observe certain basic and easily understood requirements.

The primary objective in glass cutting should not be merely to sever the sheet but to score and breakout so that the resulting cut edges have good quality surfaces, free of nicks and chips. A nicked or chipped edge is a weak edge and can contribute to glass failure.

The Score Line:
A glass cutter does not and cannot cut glass in the sense of shearing, sawing or routing. A glass cutter is a force generator. By rolling on the surface, the cutting wheel develops a system of forces in the glass so that a minute fracture, called a fissure, is created in the sheet. This is really a pair of compression lines that form on either side of the point of contact with the cutting wheel. Bending the glass causes the glass to take the path of least resistance between the compressed lines and split. A good quality cut edge can be attained at break-out only if a proper fissure was made by the wheel.

The fissure which will yield a good, clean, and strong edge is practically invisible when the glass surface is viewed. However, it can be seen by looking into the glass at an angle. The good fissure will reflect light and appear as a continuous band of light. No chips of glass dust should be on the surface if a proper fissure is made. A white gritty line indicates a gouge or scratch has been made, not a true fissure. The surface of the glass has been crushed, not scored. It's possible a piece can be broken out along a gouge or scratch but the edge will be chipped and weak. Return to top:

Score Lubricant:
The use of cutting oil on the score line significantly improves the quality of the score and subsequent breakout. A "dry" cutter should be dipped after every score. If a problem persists in cutting glass, consider applying cutting oil directly to the glass with a small brush. An "oil cutter" automatically lubricates the score line as it is being made. It also has a wheel of carbide steel and stays sharper much longer. Serious glass workers should be using oil cutters. An oil cutter will pay for itself in overall length of useful life, and will result in more successful glass cutting.

Holding the Cutter:
The traditional way to hold the glass cutter is between index and middle fingers with the thumb and index finger on the flat spots of the cutter handle. This will be ideal for the best control and vision. When the cutter is held in this fashion it is usually pulled toward the operator. However it is not critical whether it is pushed or pulled. The most convenient and comfortable grip and direction is always best, provided the following requirements are observed: 1) The glass surface along the line of the score must be clean before the score is made; 2) The wheel must roll freely and be in direct contact with the glass to develop the proper fissure. Before attempting to score the glass it is vital the wheel be lubricated. Return to top:

Cutting Force and Speed:
The most common error in glass cutting is TOO MUCH PRESSURE. The force applied on the cutter is dependent on the wheel angle, the condition of the wheel and on the type and thickness of the glass. The maximum force which should be applied is easily defined. It is the greatest force which can be used without crushing the glass surface. When the score becomes a white gritty line the maximum force necessary has been exceeded. Some practice is required to get the feel of applying the maximum force without crushing. It is essential to maintain this force uniformly throughout the full length of the score. If the force varies then the depth of the fissure will vary and affect the quality of break. When scoring and applying the maximum non-crushing force, the score must be continuous until the wheel runs off the edge of the glass.

The depth of fissure is directly affected by the speed of cut. The faster the wheel rolls, the deeper will be the fissure. There is an inverse relation between force and speed. As the speed is increased, the force must be decreased to avoid crushing and gouging. Generally, the faster the score (below maximum non-crushing force), the better the cut. What is important is that the speed be maintained uniformly throughout the cut until the wheel drops off the edge of the glass. Never retrace the line of cut. A score can only be made once. Retracing only creates a gouge and damages the wheel.

Verticality of the cutting wheel must be maintained in scoring. When the cutting wheel is tilted tot he left or right, the angle presented to the glass changes and affects the quality of score. Keep the wheel at right angles to the surface of the glass. Return to top:

Summary for Scoring:
In summary, the requirements for good scoring are:
1. A good cutter.
2. A firm, flat, clean support for the glass.
3. Clean glass.
4. Cutting oil.
5. Not tilting the wheel to left or right.
6. Uniform application of force and speed, maximum non-crushing force.
7. Always do the hardest cut first (inside curves).
8. A score clean of glass chips and barely visible when looking at the surface of the glass.

The quickest and easiest method of breaking out the score is to bend the glass, pushing up from the side of the glass opposite the score line while giving some lateral pull. Position you hands by curling your fingers toward yourself on the bottom side of the glass (the backs of your fingers should be touching) and pointing your thumbs away from yourself on the top surface of the glass. The fleshy part of your thumbs should be touching each other. (Think of your hands being in a "Praying" position except your fingers are not straight but curved back toward yourself. The glass is under your thumbs and resting on top of your fingers.) Start the run at one end of the fissure, running the score toward the point of the piece you wish to keep if the score is at an angle to the edge of the glass.

A very slight angle of bending is required, rarely more than 2 or 3 degrees. On straight cuts, as soon as the break starts, it will rapidly run the entire length of the score line. However, in doing a curved score the proper procedure is to do a "controlled run". Rather than running the entire length from the edge of the glass, a controlled run consists of giving a very slight bend with breaking pliers trying to get the score line to run a very short distance (1/2" or so) then moving the pliers to the visible end of the run just created and continuing the run another short distance until the run has been completed from end to end. It may be necessary to hold the glass at one end of the score line and give a slight wiggle and lateral pull to release the glass from the score line. After seperating the glass it's a good idea to wipe off the bottom edge of the glass piece being saved in order to remove the sharp edge generally left on the bottom side of the glass. Use the other piece of glass or the cutter or pliers you're already holding in a very shallow wiping action coming up and away from the bottom of the glass.

Other methods for breaking out the glass are:
1. Align a straight score on large sheets just inside the table edge, lift and firmly snap the glass down.
2. Running pliers can be used on straight lines or to start slightly curved lines. Align the top center of the pliers with the score line and squeeze the handles.
3. Breaking pliers would be used where a controlled run is desired and where the piece being removed is too small to grab with thumb and fingers.
4. For inside curves multiple arcs need to be made and broken out, leaving a thin strip to be broken out at the final score line.
5. Tapping is used on certain scores, usually curves, as a last resort. Hit the glass on the side opposite the score line using the ball end of your glass cutter. It is necessary to have some mass to the glass on each side of the score line for tapping to work properly.
6. Grozing is the use of breaking or grozing pliers to nip the glass away a small piece at a time. It is usually used on inside curves or narrow strips.
7. If all else fails, there's always the grinder.

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Pattern Cutting:
As a general rule, always do the hardest cut first. Glass tends to run in a straight line. This means inside curves should be done before any other cut is made. It will be most efficient to place the pattern to be cut with the inside curve facing the raw edge of the glass. If something goes wrong, the pattern can be backed away and tried again, resulting in less glass and time wasted. It is also hard to run very thin strips of glass without getting ragged, chipped edges. Allow a 1/4" margin minimum distance from the edge of the glass when placing the pattern on the glass unless the edge is going to be used in its entirety.

When scoring around a paper pattern it is necessary to steer (turn) the cutter in the proper direction. The paper will not turn the cutter for you. By keeping the cutter vertical you can easily twist the cutter so the wheel is pointing and rolling in the direction you intend it to go.

Alternatives to using the paper pattern directly as a guide in cutting glass are to outline the pattern paper on the glass with a pen or to draw the pattern on the glass while it overlays the drawing. You would then follow the inside edge of the pen line with the cutter.