Learning How to Glaze
Cutting holes or circles in glass, or drilling holes in mirrors, need not be a job only for the expert.
With care, the right tools and some patience, the handyman is quite able to cope successfully with such tasks. Leaded window lights may, from time to time, need replacement of panes, or the frames may need repairing.
If tackled systematically, this is no more difficult than other types of glazing.
Cutting holes and circles
To cut circles or holes you need a tool called a radius or circle-arm cutter. This is a cutting wheel, mounted on an adjustable arm, which revolves on a central pivot and suction cup.
The length of the arm can be adjusted to vary the radius of the circle. This tool is much easier to use on glass in a flat position, though it is possible, with care, to cut a circle from a fixed pane of glass.
To find the centre point, mark diagonals on the piece from corner to corner, with a felt-tipped pen or crayon. The intersection of the diagonals gives the centre.
If the circle is hot to be cut in the middle of the glass, mark out a rectangle in the chosen area and work accordingly. Measure off, along one diagonal, the exact radius of the circle to be cut, from the point where the diagonals cross.
Fix the suction pad on the cutter on this central point 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 round.
The pivot must be held down firmly on the glass while the cutter wheel revolves.
Once this is completed, move the cutting edge about 20mm inwards and scribe a second circle. This is known as the ‘safety circle’, because it helps to keep the edges of the glass from splintering.
With the metal tip of the glass cutter, tap the underside of the glass upwards towards the cuts. Work slowly and carefully around both circles. The object is to ‘open up’ the cuts so that the removal of the waste glass is both clean and neat, without splintered edges. Tapping out could take 10 or 20 minutes-and there is no advantage in rushing it.
Next, divide the safety circle into wedge sections, using the ordinary glass cutter. Cross-hatch these wedges and, with the head of the glass cutter, tap out one small piece of glass from beneath, then carefully break out the glass in the safety, circle with pliers.
Next, make radial v-cuts to the line of the outer circle. Take care not to mark over this line, or the glass may shatter. These score marks should be at intervals of about 25mm and are broken out with pliers. First tap and then break out glass until the whole of the opening is cleared.
Drilling should be done using spade or spearpoint bits, which are made especially for glass drilling. Acan be used at a slow speed, but a more reliable method of drilling is by using a bit and brace. The speed of drilling should not exceed 350 revolutions per minute.
Holes should not be drilled closer than 13mm from the edge of a glazed surface and, if possible, keep this to 25mm. Where a masonry drill is not available, a tapered triangular piece of file may be used, with care, in a brace. The turning motion should be slow, steady and with even pressure.
The glass should be laid 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, to prevent the bit from wandering while drilling.
When drilling a mirror, start on the non-reflective side, to prevent damage to the silvering. To find the drilling position, cross measure from the outside edge of the glass. Avoid too much downward pressure as this may fracture the glass.
Make a small well of putty around the drill hole and fill this with turpentine or white spirit; with mirrors use water as oils will cause staining beneath the glaze. When you begin drilling, the spirit will turn white with powdered glass; when this happens add more spirit.
Just before the hole breaks through the glass, stop for a moment and clean away debris. Proceed carefully as the bit nears the other side. Do not stop turning or you will run the risk of splintering the glass around the edge.
There is a danger that the drill may ‘break out’ a large sliver from the face side of the mirror if you drill only from one side.
It is a good idea to finish off by drilling from the face side just before the bit breaks through from the back. Again. Mark accurately from the edges and drill with great care.
10. November 2011 by admin
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