A lesser known, but very successful athlete once said;
“Do today what others won’t, so tomorrow you can do what others can’t.”
Back in 2012, we took the hard road of starting our own eyewear factory with one goal in mind. To make our own sunglasses frames in-house.
Nearly a decade later, we’re now one of three eyewear manufacturers in the UK; the only one in Scotland.
No easy task.
But easy never made great.
Making acetate sunglasses
First, large sheets of 8mm cellulose acetate are cut into strips using a circular table saw. This makes them more manageable to fit inside our CNC milling machine which cuts the frame fronts.
Next, the frame fronts are machine cut using various cutting tools to achieve their shape and required accuracies. As many as 30 machining stages are applied at this stage.
Frame fronts are hung on our workshop frame-wall in between processes. This keeps them organised whilst we machine acetate temples.
The temples are also CNC machined from flat sheet acetate. At 6mm thick, they're slightly thinner than the frame fronts but still thicker than the industry average.
After machining, the frame fronts and temples are sharp and have numerous cutting marks. To remove them, they need to be smoothed using a process known as tumble polishing.
This process requires motorised octagonal wooden drums which contain 20-30kgs of small beech polishing pegs. Mixed with various oils and coarse pastes, the frames and media are then sealed inside the drum for 'tumbling.'
The tumbling process churns the frames and temples around and around creating friction with the beech polishing pegs. After 24 hours of continual polishing, this aggravation removes the sharp and rough edges from the acetate parts.
There are 4 chambers in our machine, each with progressively smoother media and pastes. Going from a rough stage (phase 1) right through a very fine and smooth stage (phase 4) the entire process takes 4 consecutive days.
In 1969, it took Apollo Eleven 3 days to reach the moon.
When it comes to quality, there are no shortcuts.
After tumble polishing, the acetate parts are poured into large sorting trays. By hand, they're retrieved from the media and gathered into groups for ultrasonic cleaning.
Ultrasonic cleaning removes all the polishing grit and any excess oil from the tumble polishing process. Also used by jewellers, this cleaning method makes them incredibly clean and ready for the next production stages.
In these images, the frame fronts and temples have only been rough tumbled in phase 1 of 4. However, you can see how they've 'frosted' from the rough tumbling media which has removed all the machining marks in just 24 hours.
Look closely and you'll see the polishing paste which has built up inside the little rivet holes. This is why ultrasonic cleaning is so effective. Using sound waves, it blasts the grit out the smallest of crevices to make the parts clean.
Next, the frames are hand polished using 4 increasingly finer grades of wax compounds. Like the tumbling phase, it makes the acetate smoother and smoother until the surface is a lustrous, glossy finish.
Every surface is painstakingly hand polished to achieve an impeccable shine.
Various widths of polishing mops are used to reach inside the bridge aperture. This lets us achieve a consistent surface finish over the entirety of the frame front.
Hand polishing is a highly skilled task and requires good feel. Too much pressure can burn the acetate with friction from the wheel. It takes experience to achieve the best possible shine, free from scratches or imperfections.
Fluffy mops are used to give a final gloss finish on the frames before assembly. This is the final stage of hand polishing and is also the most crucial.
These finishing wheels tend to 'snag' more than rougher mops, so if the worker isn't careful, the frame can get caught and then 'thrown' against the back wall of the polishing booth.
Patience is key.
Thin gloves are worn to keep polishing wax off the skin. But they also provide greater dexterity and feel compared to thicker gloves.
As seen in the image below, the sunglasses frames have gone from a rough frosty texture to a glass-like finish. After 8 stages of polishing, this is the result.
To fit the 5 tenon hinges, the frame fronts must be drilled out using a precision drill-press. This make the holes for the rivets to pass through the 8mm acetate.
By using a drill press, the rivet holes can be made fresh. This keeps any debris from getting inside the frame and later being trapped by the hinges.
Once drilled, by hand, the 5 tenon hinges are then permanently fastened to the frame fronts and temples.
At Banton Frameworks, we used solid nickel rivets to attach our hinges. This is considered the old fashioned method, but yields a solid joint between the frame and hinge.
Rivets have been used since 2,000 BC to hold things together.
A tried and tested method.
Some satisfying results on the workshop assembly table.
So the sunglasses fit properly, a very precise angle is cut into the frame fronts and temples.
This angle is known as a mitre which allows the temples to open to the correct width for your head. Too wide and the frame would be loose, too narrow and you couldn't put the sunglasses on your head.
A very precise process which takes careful calculation.
The sunglasses frame front is 'butted' against a guide bar and which braces it for cutting. A set of pincers locate into the hinge creating a secure hold of the frame.
Using a lever, the frame is then ran past a slim rotational blade which cuts the angle into the frame.
Once more, the worker needs good dexterity and 'feel' to achieve a good quality of cut.
In the image above, you get a better view of the angle cutting process.
Cutting the accompanying angle on the acetate temples is a very similar process. The pincers locate into the hinge before the acetate is cut.
It took us 5 months to acclimatise to using this particular cutting machine. Getting the angles right takes a methodical approach which has resulted in the high-quality articulation of our handmade sunglasses frames.
After cutting the frame fronts are finally assembled with two temples.
However, the temples are still straight, therefore require precise heating and moulding using this temple bending machine.
Using a rotational heater, the temples are located inside to become soft and pliable. This takes several minutes, so the frames do a full rotation inside the heater before being moulded.
They go in cold and come back out hot.
A toasty carousel.
Once properly heated, the temples are them located inside a pair of mould 'jaws.' These are electro pneumatically controlled, which provide a series of six curvatures, all in one sequential process.
These curvatures make the sunglasses frame comfortable to wear and make them secure behind your ears.
A before and after of the temple bending machine in use.
Hopefully you found this walk through interesting.
Thanks for stopping by.