MODERN GLASS-CUTTING

Glass-cutting is carried out today in numerous industries, often by skilled operatives, equally often by automatic machines. This includes the cutting off during manufacture of successive large plates, from continuously extruded glass sheet, for plate-glass windows are made thus. In some plants operatives hand-cut about 300 square yards of glass a day. Glass tubing for a host of purposes is often cut within the tube by a rotary scribing movement. An adjustable collar fixes the length of tube to be cut off (see Fig. 11).

For large discs, such as clock faces, a beam compass with a Diamond point is used to swivel round in a circle. The disc is separated by tapping.

In the manufacture of bottles, electric lamp bulbs andnumerous other shapes, it has long been a common practice to make these by automatic methods. A blow tube on the machine picks up a lump of molten glass from a furnace. Up comes a mould of the desired shape and closes round the glass, the tube rotates and a puff of air blows out the glass blob which then takes up the desired shape in the mould. The, moulding former drops away, and the bottle or bulb moves on. The neck is then scribed by a Diamond. Often a small pointed flame is applied to the Diamond cut, followed by pressing a cold steel bar to the region. A clean split results, and the bottle falls off on to an endless belt and is carried away.

Glass-cutting Diamonds are used extensively for the pro duction of circular, curved or oval pieces of glass. This not only includes mirrors of a variety of shapes, but also, on a much bigger scale and of more importance, the cutting out of spectacle lenses. The Diamond is fitted into a machine on pantograph specially designed for the purpose. The shape is cut from a glass plate, the surrounding area being broken off with pliers. So efficient is this Diamond glass-cutting operation that as many as 10 000 lenses can be cut with a single small Diamond, despite the fact that a wide range of shapes is in demand by the spectacle maker. The Diamond edge ultimately deteriorates and either a new edge is formed or, more fre­quently, the Diamond is simply rejected. Clearly the cost per lens is very slight, so that the economic efficiency is very high.

The very hard ceramic glazed tiles used in bathrooms, fireplaces, and so on, often need to be cut to shape or to fit odd corners, and for this purpose the simple and fairly cheap glazier's tool is by far the best.

We ourselves have made a study of the edge of a Diamond after cutting prolonged lengths of glass. We found severe wear after one mile of cut, but the particular tool we employed was still reasonably sharp after 10 miles of cut.

Many operatives maintain that a better cut and a longer life are secured by dipping the Diamond into paraffin oil first, the lubrication being of help.