Glazing, windows and doors

Preparations for cutting glass

Great care is needed when cutting glass. Professional glass cutters wear protective wrist bands, since a splinter of glass could cause serious injury. It is advisable, then, either to wear wristbands or to wrap your wrists with household bandages or something of the sort before cutting glass. You will also need a large, fiat surface to lay the glass on, such as a kitchen or dining table. Place the blanket on the table to protect it and the surface of the glass from being scratched. Where odd shapes must be cut, always make a template first from a stiff card, carefully checking its accuracy. Be sure to make this 3.2mm (|in) smaller all round than your measurements to allow for the distance between the edge of the cutter and the cutting wheel. A steel wheel glass cutter is adequate for nearly all types of glass cutting and is also much cheaper to buy than the traditional glass cutter’s diamond.

Try to choose a cutter on which the wheel is clearly visible while the tool is in use, as this will promote greater accuracy. If you anticipate doing a large amount of cutting, you may find it useful to buy a good T-square to guide the cutter through the stroke. You will also need a ruler or steel tape for measuring. To mark the glass, a felttipped pen, chinagraph pencil or crayon can be used. Straight cutting Before doing any cutting, clean the surface of the glass by wiping it with a proprietary glass cleaner, such as Windolene, or with some methylated spirits. Mark the cutting lines on the surface and re-check the dimensions before cutting. Lubricate the glass cutter beforehand by wiping it over a piece of felt which has been soaked in light machine oil.

Hold the cutter so that the handle rests between the first and second fingers and the bottom of the hand remains clear of the glass. With a straight edge held 3.2mm (|in) from the marking line (to allow for the thickness of the wheel), score the surface of the glass along the line with the cutter. Cut with a firm, smooth stroke, drawing your arm back while keeping the rest of your body still. Do not backtrack, as the glass may break at a point other than where you want on your cutting line. The scoring should be completed in one operation—the object being to score the surface of the glass evenly so that the piece can be easily snapped apart. Once the score mark is made, lift the glass and tap it gently from underneath along the length of the mark. Then position the edge of a small batten, about 50mm (2in) wide, directly under the cutting line. Place your hands on the glass surface, one on either side of the line and as close to it as possible, and press down slowly and firmly with your fingertips until you get a clean break along the cutting line. Where you need to remove small strips or pieces of glass, score the line as before and then, using the jaws of a pair of pliers, break off the waste pieces in small bits. Do not use the notches along the outside of the cutting wheel for breaking off small segments of glass—they are intended only to be used as gauges. Curves and angles can also be cut by scoring the glass to the shapes required from cardboard templates. Once the glass has been scored to the shape, tap it carefully from the underside and then, gripping the piece firmly on each side of the score marks, snap evenly downwards to break the glass.

Cutting circles

A special instrument called a radius cutter is needed to cut accurate circles in glass. This cutter is best used with the glass resting on a flat surface, although it can be used on a window which is already in position. It consists of a cutting wheel mounted on an adjustable arm which revolves on a central pivot fastened to a suction cup. The first step in cutting out a circle is to find the centre point by marking diagonals on the piece from corner to corner. If the circle is not to be in the centre of the sheet, mark out a rectangular area where it will be and work accordingly within this area. Do this with a felt-tipped pen or crayon and then measure off the exact radius of the circle to be cut along one diagonal, beginning from the point where the diagonals cross. Fix the suction pad of the cutter on this central point where the diagonals meet and set the arm so that the cutting edge just reaches the length of the radius. Now scribe the circle, holding the cutter firmly and applying even pressure all around. Once this is completed, move the cutting edge in about 19mm (fin) and scribe a second circle—this is known as a safety circle because it helps keep the edges of the glass from splintering and cutting your fingers. Using the metal tip of an ordinary glass cutter, tap the underside of the glass upwards towards the cuts. Work slowly and carefully around both circles—the object of doing this is to open up the cuts so that the eventual removal of the waste glass is both clean and neat, without any splintered edges.

Drilling glass

Normally, the only type of glass you will need to drill will be mirror glass in order to provide holes for the fixings. Special bits, made expressly for the purpose of drilling glass, should be used with a hand drill or brace. Power drills are generally not suitable (unless fitted with a speed reducer) because the speed should not exceed 350 revolutions per minute. First, lay the glass on an absolutely flat surface. Mark the drilling position by pressing the tip of the bit on to the glass. This is to fracture the surface which will, to some extent, prevent the bit from wandering while drilling.

Remember to start on the nonreflective side to prevent damaging the silvering. Lubricate the end of the bit with turpentine and begin drilling, keeping the drill at right angles to the surface. Do not use too much downward pressure as this will break the glass. The powdered glass thrown up by the bit will turn the turpentine white and, when this happens, more turpentine should be added. A useful tip is to make a small ‘well’ around the drill hole with a ring of putty to contain the lubricant. Proceed carefully as the bit nears the other side, but do not stop turning or you will run the risk of splintering the glass around the edge and ruining the piece.

Removing rough edges

After the drilling has been completed, any rough edges can be smoothed away using two Carborundum stones—a No. 121 fine and a No. 122 medium. You will also need a natural pumice stone, some pumice powder and a wood block. Both the Carborundum and the pumice should be kept wet at all times when being used. The first stage, called ‘arrising’, removes the sharp edge. Use the medium stone for this, holding it at an angle of 45°, and rubbing it downward in one direction. Once the edges have been arrised, the flat part of the edge can be ground with the face of the medium stone. Rub it up and down, keeping it in contact with the glass at all times. Follow this with the fine stone to produce a sheen. Basic polishing can now be done with the pumice stone.

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