Tender's sunglasses frames are made from cellulose acetate, derived from cotton pulp. This means that as well as being a natural, biodegradable product, they're hypo-allergenic. A lot of cellulose acetate for top-end frames is made from lignin (from wood pulp), but cotton pulp makes a finer material, which can take a very high polish.
The acetate sheets com like this:
The first job is to make a pilot hole in the centre of where each lens will be:
Now the fun starts! Matt (photographed above, who made the glasses from start to finish), made an original pattern for the frames by sticking a paper print-out of my drawing onto a sheet of acetate, and cutting around the lines freehand. He mounted this pattern onto a block, and it goes into a machine that allows him to copy a shape with the router. This is still a very skilled job, and is done one at a time, controlled entirely by hand. One slip and the frames would be ruined:
The pink pair, below, is the pattern, held in place by screws through the guide holes. The black block is in the process of being routed out.
The router bit in the black pair is spinning very fast, cutting into the black acetate. The bit on the pink pair is just a smooth static pin, but in the relative same place as the router bit in the 'live' black pair. By tracing round the contours of the finished pink pattern with the static bit, a perfect copy is routed out of the black acetate by the spinning router.
The bed holding both blocks is on a track, and can be moved around by two handles on the front:
Now starts a very long process of tidying them up, entirely by hand, with small, specially-shaped, files, and fine sandpaper:
Now the front are clean and neat, and ready to take lenses, they have to be made a bit more face-shaped. The first job is to make the nose bridge bump. This is done by heating up the frames over a line-bender:
The next job is to route out the groove which the lenses will snap into:
The next job is to apply the pre-made nose pieces:
The sides (temples) of the glasses, are made in a similar way, but first they need to be reinforced with a wire core.
The end of the temples with the wired-hinge sticking out is sawn off, to make way for a much bigger, stronger, riveted hinge:
After cleaning and filing the temples, again by hand, they have the hinges riveted on:
These hinges are much deeper, and more robust, than the standard ones attached to the temple wires. In fact, they are so wide that they were really difficult to attach (there's only a millimetre or so of space between the edge of the hinge and the edge of the temple). The solution that Matt came up with was to leave an 'ear' of acetate either side of the hinge, to give him something to hold onto while positioning the hinge. Then after it's riveted on he removes the ear with a file, leaving the hinge perfectly in place.
The final job, and probably the most skilled, is polishing. This not only makes the frames shiny, it also shapes them to a large extent. polishing takes a long time, about 10 minutes per frame section, on each grade of polish, and there are 3 frame sections to a pair of glasses, and 4 grades of polishing!
Finally the UV protective grey-brown lenses are popped in, and a cotton cord is tied through the holes at the ends of the temples. Then the glasses are wrapped in an english-made handkerchief of english-woven cotton satin, and they're ready to go!