Edging Equipment - Part 1 General description and auto edgers

摘要

Once, the edging technique included cutting the lenses into a shape roughly approximating that of the required lens, using a diamond cutter. The lens was then hand edged to the finished shape, using a ceramic wheel of large diameter (about 24 inches). The finished result depended entirely on the expertise of the glazer. At this period automatic edgers were not available. The first 'improvement', which took place in the mid part of the last century, was the introduction of rudimentary auto-edgers. These used mechanical controls and the lens was cut using two wheels - one for rough cutting to shape and the other to apply a 'V' bevel to the edge. This meant that thick lenses always had a wide unsightly bevel, which protruded beyond the rim of the frame. On minus lenses 'power rings' were inevitable, due to internal reflection at the lens edges. To obtain the correct shape, the machines required a 'former' (as still used today), which would either be supplied by the manufacturer, or cut on the premises. To cut the former, the operator had two options - either to use a thin plastic blank, or to cut one from a metal sheet. These metal formers were cheap, but quite effective if used correctly. However, cutting them did require some skill. A metal blank (with a blue coating on one surface) would be placed on a cutting table and the frame clamped above it; the rim shape was then traced onto the metal, using a sharp stylus. This cut a line into the blue coating, leaving an outline of the required shape. A pair of tinsmith's 'snips' were then used to hand cut around the shape. The lens was then cut in a similar fashion to that used on today's auto-edgers, but the finished size after the first cut might not be the exact size required. In fact it normally wasn't. The second re-sizing cut had then to be carefully carried out, as the accuracy of the machines were not always as good as they should have been. It was quite easy to take off too much material, especially for plastic lenses, where the softer material could be cut away too quickly - especially at sharp corners. The resultant lens might have gaps around the edge, hence necessitating the frequent use of packing material. The types of mechanical control and earlier types of drive motor, prevented designers from overcoming these problems. The machines produced the best results possible, at that time.