Have you ever wondered what it takes to prepare a pair of glasses from scratch? Every pair of prescription glasses or sunglasses has a story. Today you can access eyewear the same day by various brands like Overnight Glasses, Warbyparker, Zenni Optical providing next day prescription glasses services. But have you ever tried to find out how these eyeglasses are made?
This article will help you understand the various steps involved in manufacturing your beloved eyeglasses.
You must have noticed every pair of glasses is composed of a frame and lenses. This article will briefly discuss the manufacturing techniques behind these two essential components. Every step from selecting the raw material to final polishing will be discussed briefly.
The lens is the part of eyeglasses through which we actually see an object. Generally, we see two basic kinds of lenses;
- Plastic Lenses
- Glass Lenses
Let’s have a look at the manufacturing of these lenses.
Round pieces of plastic, polycarbonate, selected in variable thicknesses, are received as raw materials for plastic lenses. The nominal thicknesses for such plastic blanks are 0.63~1.9 cm. Some of the other materials used in developing plastic lenses include; chemicals for adhesion, metal, and certain dyes and colors.
First of all, the lenses are designed to match the size and shape of various frames. The spherical lenses, i.e., concave and convex, need one ground curve at each lens. Whereas, to prepare lenses for astigmatism, multiple curves are required. Do you know that power of a lens is established by the number of curves and degrees of curves in a lens?
After the design stage, various treatments like tint, coatings for protection against ultraviolet rays, and scratch resistance are done prior to fixing lenses inside eyeglasses frames.
The Blocking Process:
The lens blank, as discussed earlier, is placed inside a machine known as a lensometer. In this machine, the optical center is marked on the lens. The optical center is the point that has to be right above the user’s pupil. Each plastic blank is then placed inside the blocker machine. The blocker machine contains heated lead alloy, which fuses the block to the front side of the lens.
The grinding machine is then used to carve out special curves on plastic blocks. These curves are cast on the backside of the lens. After this stage, polishing or finishing is done.
In this step, the lenses are placed inside a fining machine. Sandpaper is used to rub the lenses. A metal lap is selected, and the front of each lens is polished with it. Hot water is used to dip in the lenses for a few minutes. Another coat of polishing is done by placing lenses inside a fining machine.
As you can infer from the name, beveling is done using an edging machine. Water continuously flows over lenses in this stage, and a bevel is placed around the lens. This is imperative for holding the lens inside a frame.
A silting disk or glass saw is used to cut glass slabs. After that, a round blank is carved out of a glass slab which is mold and pressed into the desired curvature. The glass blank is ground or lapped by using abrasives like diamond or carborundum.
The grinding is done using a cup-shaped tool to make specific curves on lenses for making concave and convex lenses. Both tool and lens rotate to shape desired curves. After making curves, smoothening or grinding is done using emery flour as abrasive. Polishing, a slow-paced process, is done with a tool soaked in wax. The lens is rotated to and fro against the polisher. The diameter of the lens is adjusted by grounding it around the edges after polishing. The final glass lens is tested to form an image of a point source or other suitable object.
Generally, metal or plastic is utilized as raw material in manufacturing eyeglass frames. A derivative of cotton, cellulose-acetate, being strong and flexible, is molded into thin sheets slightly thicker than eyeglasses frames.
As soon as the specific design of the frame is decided, a die is made out of steel. A machine known as a blanking machine is used to punch blanks out of the cellulose sheet mentioned above. The frame fronts are finished. Grooves are carved, and frame edges are roughened with two abrasive machines. Attachments like nose pads are added by fixing the frame in a vice.
The two side arms known as temples are also carved out of cellulose sheets. The standard length is 5~6 inches, and these temples connect with the frame body through hinges. A capitron machine is used to connect temples with the body efficiently.
The finishing stage is most important as it generates the overall look of the eyeglass frame. In this stage, rubbing, polishing, and grinding are done using various techniques. In this stage, the quality check is done as per parameters set by FDA.
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