Prototyping 3 - Polishing the polycarbonate element

After the success of cutting and polishing the acrylic elements to such a high quality, the manufacture of the central negative polycarbonate element was a complete let down. Lets cut straight to the chase, polishing polycarbonate is a nightmare. Having made the two acrylic lenses without a problem, the polycarbonate element has come out slightly hazy with so many scratches that it rally is useless as a lens. Wen looking through 2 stacked acrylic elements, the image is crystal clear. However, when I put the polycarbonate element between them in the system, the image is destroyed. This is obviously unacceptable, as results in yet another useless lens. Two things have been against me on this one, which I will explain below:

• Firstly, the polycarb lens is double concave. It follows the standard design for a cooke triplet and is a negative element. The polishing process i have designed struggles to polish concave surfaces like this. The pad, obviously larger than a tip by nature, covers a wide surface area. Annoyingly, this causes large contact with the surface around the centre of the lens and causes the pad to grip and spin, defeating my trusty bluetack. Also, I have programmed the pad to run from edge to edge of the lens surface, but as the pad reaches he extremity it starts to take away the rim rather than wear evenly. Both these problems can be resolved by using smaller pads, stronger grip between pad and tool, and programming the tool to travel close to but not upto the very edges of the surface.

WOW LOOK AT THAT AMAZING IMAGE QUALITY.......
It's staggering to think that the PMMA elements are perfect, but because the PC element is flawed, the entire system
is completely fu......

• The second problem is a little trickier to solve. It comes down to the polycarbonate itself, and my lack of knowledge on the material. With use in the prescription glasses industry, I am certain that polycarbonate lenses can be polished to a perfect finish. However, I haven't yet found a good solution on a small scale to polish the element to be as crystal clear as the PMMA ones. From my limited experience with the material, I know two important things. Polycarb is extremely hard, and it can also appear foggy if polished wrong. The hardness makes it difficult to remove scratches, while the fogginess is something that I was unaware of until now and means that surface temperature, which can get very high while polishing, must be kept down. My next step is to research polishing methods for polycarbonate and see if i can come up with an improved method.