ROV Porthole

One feature that almost goes without saying for a ROV is a video (+ possibly still) camera. Imagine being able to hover around reef systems, or around the piers and see all the little fish swimming around. To make this possible a viewing hole must be installed which will allow the camera to have a view of the outside world.
I made the viewing hole from 4mm Perspex salvaged from an old fish tank. To get the round shape (which fits in the groove of the endcap - see pics) I embarked on the following process.
1) I covered the Perspex in contact on both sides to avoid scratching the surface
2) I scribed the design onto the Perspex using a circle I generated in MS Word and a hobby knife
3) I used a hand jigsaw (like a mini hacksaw) to approximately cut of the perplex. I had wedged the Perspex between the table and a piece of MDF - thanks to Adam for that suggestion.
4) I clamped a file into my bench press so that it made an angle with the jaws of 90 degrees. Using the jaws as a guide, I spend the next few hours shaping the Perspex to meet the lines I had scribed - regularly checking if it actually fit.

After drilling the 75mm hole in the end cap I affixed the Perspex using silicon specifically targeted at watery applications (recommended for aquariums and the like.