I decided also to put a fan into the window itself. I positioned this so that
it would be blowing air above and below the AGP port (providing air to the CPU
above and the GPU below). I measured to find where this position would be on
the perspex and got out my compass for a radius of 40mm (for an 80mm fan). I
made it so the fan would be an equal distance from the two closest edges of
the perspex, i.e. so that the centre of the fan was on the diagonal of the square
window.
To cut the perspex out, I clamped it down tightly to prevent vibrations that
might shatter the perspex. I then drilled a hole large enough to fit a jigsaw
blade through in the middle of the circle I was going to cut out. When the drill
broke through it tended to shatter the perspex on the other side; by drilling
in the centre, no cracks would reach outside the circle into the rest of the
window. Using a metal cutting jigsaw blade I went round slowly cutting a few
mm then pulling back to allow the blade to cool. With this piece, this didn't
seem necessary as it showed no sign of melting anyway. Once it was cut I rounded
it off nicely with a dremel and then sanded the internal edge with some 400
grit sandpaper to get it supersmooth.
The last bit of work to do on the perspex was to drill 4 holes to hold the
fan in. I only used 4mm drill bits (slightly smaller than the thread on standard
fan self-taping screws) as it would be easier to get the drill in the right
place and would hopefully avoid shattering on the other side. I placed the fan
over the top and drilled into the perspex a little to get the centres in the
right place, then removed the fan to drill all the way through.
