In presenting the basic principles of these two disciplines, I've oversimplified somewhat for the sake of brevity. You exchange the goods for the pennies and place the item on the two penny table. Depending on the equipment, the lens may be held in place by special adhesive pads, with a special alloy that "glues" the lens to the block or with plastic. As it operates, the slowly turning lens is brought into the fast turning cutting surface, which is either a grinding wheel or steel blades, until a guide contacts the pattern, which is rotating to match the lens.

2.50 cylinder, for example, to match -2.00/-2.50 generated curves), and the lens and x finance calculator block are rubbed together. For example, the vast majority of labs now use computers to determine curve parameters and lens choice, and equipment is available that will combine several steps or even do the entire operation automatically. If the lens gets too hot during the operation it may warp or tear, so it is cooled by water, which also washes away the cut material (called scarf). Newer edgers do not use patterns; instead, the shape is determined by a probe that measures the frame and stores the information in a computer, which in turn controls the edging operation.

Lens thickness is determined by curve type (plus or minus), lens material (some plastics are tougher and may be ground thinner), or other considerations (safety glasses, for instance, are made thicker than lenses for everyday use).

Step 6: The curves are set on the machine and the lens is generated (ground). Step 9: The lens blank is shaped on a linear lathe (called an edger) using either a ceramic or diamond grinding wheel or stainless steel blades. Glass lenses are ground and polished much the same way as plastic except that diamond cutting surfaces are used, and some details may vary. Also, special UV blocking dyes may be applied in the same way. Special dyes are kept in heated containers and the lenses are immersed.

Weekly conversations are held. The finished eyeglasses are then thoroughly cleaned and packaged for delivery to the patient. A small chuck receiver is placed where the geometrical center of the finished lens will be, and the lens is then oriented on the 180 axis.

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Millions of years ago during hunter-gatherer times, there was no linen, silk or cashmere. There are many ways you can make your brother’s birthday special. Indeed, tanning a raw animal hide by hand in order to make leather is neither clean nor quick.