Group 12-13 '15
How Are Spectacles Made Traditionally?
Eyeglasses frames are typically made of either metal or a type of plastic called cellulose-acetate. Cellulose acetate is derived from cotton and is flexible and strong.
The Manufacturing Process
Die-cutting plastic frames
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After the design is decided, a die is made out of steel and is fitted in a blanking machine that punches blanks out of the sheets of cellulose-acetate. The edges of the steel rule die are sharp, and the dies have protruding rods that are used to remove the punched fronts where the lenses will be fitted. The acetate sheets are brought from a cool storage area to the blanking room where they are heated in small ovens to about 180° F (68° C) to soften the plastic. The soft sheets are fitted into a blanking machine, and, under several tons of pressure, the die cuts through the plastic to produce a blank. The machine is automated to lift the die and move it to the next portion of plastic. The blanks are produced quickly while the plastic is soft. The blanks are then removed from the sheet, and the lens portions are taken out of the frames. The lens blanks become scrap.
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The blank frame fronts are finished in a series of operations. Grooves to hold the lenses are cut using a router. The frame is held tightly by a holding fixture made of aluminum and consisting of two pieces. The fixture is fastened around the frame and pressed against the router blade. The grooves are cut to 0.16 in (0.41cm) wide, which is an industry standard. If thick lenses are needed, they are ground down along the edges to fit the routered grooves.
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The frames are then smoothed to remove rough edges by two different abrasive machines. One machine is specially shaped to smooth the edge of the frame that rests on the cheek and the second smoothes the area around the nose. The frame is then secured in a vise-like device while the nose pads or attachments that hold the nose pads are glued to the frames. Once the glue is allowed to cure for 24 hours, the glued areas are also smoothed.
Producing the temples
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The two side arms that curve around the ears are called temples. The temples are also punched out of sheets of acetate with blanking dies. The standard temple length ranges from 5-6 in (12.7-15.2 cm) and they are usually cut out of the same material or
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After the frames are smoothed, the temples are attached to the frames with a metal hinge. To make the temples, plastic temple strips are heated, and a narrow strip of steel called a core wire is also heated. When the right temperatures are reached, a core wire is inserted into the center of the softened temple.
complementary materials to match the fronts. The temples may be flat with angular edges or rounded in shape, depending on the frame style. Inexpensive glasses, like some non-prescription sunglasses, may be made without core wires, but they will also be less strong.
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To attach temples to their frame, small slots are cut in the upper comers of the frame. A half of a metal hinge is put in each slot, and the frame and partial hinges are placed in a capitron machine. The capitron machine induces ultrasonic vibrations in the metal hinges and creates heat of friction. The friction causes the plastic of the frame to melt locally around the hinge to bond the hinge to the frame; this process is more secure than gluing or other types of bonding or mounting.
Finishing the fronts
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The fronts with hinges are then imprinted with the manufacturer's name or logo, the name of the style of the frame, and the size of the frame. Before the temples are attached to the frame, an angular fit is needed to make the frame front tilt inward toward the wearer's face from top to bottom. An automatic saw is used to cut the correct angles in the upper edges of the front. Caps are fitted over the hinges, while the front is polished. By this stage, the fronts are still flat with sharp edges except in the routered areas where the lenses fit. In the polishing room, hundreds of fronts at a time are tumbled in a drum with pumice (soft stone that is ground to a powder and used as an abrasive) and small maple pegs that look like miniature kitchen matches with rounded edges and tips. The pumice adheres to the pegs, which grind against the fronts during a 24-hour-long process that smoothes the rough edges. Crushed coconut shells are sometimes used by manufacturers in the polishing process.
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The smoothed fronts now have to be shaped to fit the curvature of the face. They are. heated in an oven, mounted in a curved forming die (similar to the blanking die used to make the fronts), and placed in a press. Pressure is applied for about 30 seconds to produce a uniform curve in the front. The warm front is dipped in a cold water bath to harden it to the curved shape.
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The shaped fronts are returned to the polishing room where they pass through a series of tumbling drums over a period of four days to add the finished sheen. Each drum contains pumice that is finer than the previous one; the final drum holds polishing wax. All of the polished fronts are inspected carefully for any scratches. They are placed individually in envelopes and filed by size, style, and color.
Finishing the temples
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Depending on the shape and style of the eyeglasses design and their temples, the temples are then ground and shaped during several operations. Grooves are cut into the ends of the temples, and the matching halves of the hinges are riveted into the temples. The ends are cut to match the angles of the finished fronts. Like the fronts, the temples are then finished during multiple operations, and pairs of polished temples are packed in envelopes by size, style, and color. Manufacturers store the envelopes containing fronts and temples until optometrists or optometric supply houses order them by size, style, and color. Sets of fronts and temples are then shipped.
This information is retrieved from: