19 December 2012
Have you ever wondered how glasses are made? Probably not. But for something a little different, I'll let you know.
First of all, the lenses that come in are not pre-cut to the size of the glasses. They come in a circular disc form, rather like an oversized contact lens. This lens contains the prescription for the patient, in Spherical and Cylindrical powers (the 'Sphere' is the prescription that corrects your eyesight, and the 'Cyl' corrects someone's astigmatism). Having a cylinder on a lens is sort of like scooping a chunk for the sides, so it bends the light when you look through it, depending on what orientation it sits in from of your eye. The way this is measured is by an 'Axis'. An Axis is a number from 1 to 180, and is a measurement of degrees, sort of like angles on a shape.
So, we have a machine called a 'Focimeter', which basically tells you the prescription of a pair of glasses you put under it. It tells you everything I said before; Spherical, Cylindrical powers and Axis. It's used throughout to make sure no mistakes are made at almost every stage. The uncut lens is placed under the Focimeter to check the prescription and to line up the Axis. Then, a little lever is pulled down to dot the lens' centre, so that you look out the best part.
The frame you choose off the shelf is the one you have, sort of like clothes in a shop. Yeah, chances are somebody has put them on before you, but we thoroughly clean them. The dummy lenses are popped out, and the frame is put into a machine that clamps it down, and what can only be described as a thin and bent finger, tugs the inside of where the lens is held, and the connected computer maps the lens shape on a touch screen, where you can input the distance between pupils, the height of the pupil and the axis.
Next up, on the same machine, the uncut lens is placed on a small stand, with a camera attached. The camera shows you an on-screen grid so you can line up the three dots with the pupil distance. A small pad with a sticky side is placed onto the uncut lens, covering the dots so that in the next stage, everything is kept in the right orientation.
The 'blocked' lens is placed into a separate machine called an 'Edger' which is what does the cutting. You download the lens and prescription data from the 'Tracer' (the bent-finger-thing) and after you've placed the blocker-pad in the clamp; press start. The edger has a rotating wheel that spins hundreds of times per second, that:
•Cuts it to size •Applies a bezel to allow it to sit in the frame •Gives it a safety bevel, so it isn't sharp
(and if its a 'Supra' frame, where there isn't a metal part on the bottom half of the lenses, it will apply a groove and polish the edges).
When the machine is finished, the cut lens is removed from the clamp and placed within the frame. If its a metal frame, screws are simply loosened so you can place the lens in. If it's a plastic frame, it's heated it up make it a bit more flexible and the lens is pushed in and cooled-down, before repeated the whole process for the left lens.
The sticky pads are removed, the glasses are cleaned, and they're put under the Focimeter again to check against the prescription. Job done!
So yeah...bit of an experiment in terms of writing but be sure to know what you thought. I know I had no idea before I started this job so I was so interested when I got to do it.
Glazing • Opuss № I