A job helping a friend of my wife's move got postponed so I decided to go ahead and install the fan shroud flaps. First step was to determine how large I wanted to make the opening. I settled on 5 mm less tn the bottom and sides, and 10 mm less at the top. This would give me overlap for sealing, as well as allowing me to bolt it at the top. These flaps come with rubber fingers that are meant to hold the flap in place, but I'm running a Lexan shroud which is a lot thicker than the normal metal shrouds these are used on. Once that was done I cut a template and laid it out:
Next step was to drill holes at the corners of the opening, this provides stress relief while cutting the Lexan (and it will also stop any crack from propagating should you do something wrong):
I then started to cut along the lines. Initially I tried using my Dremel with a cut-off wheel, however it was just melting the Lexan. Next I tried this:
That did the trick. There was still some melting but unless you are using some sort of cooling fluid or going exceptionally slow I don't see how you can avoid this. Got both openings cut out and then needed to clean things up.
I tried using a single-edged razor blade which worked, but at some damage to my fingers. I then figured I'd try my straight cutters:
Those worked great. Once I had the edges trimmed I used a sanding wheel on the Dremel and a file to finish the clean-up.
Since I was going to be bolting the flaps in place I wanted something to spread the load out to avoid cracking of the Lexan and to positively hold the flaps in place. I have some thin aluminum lying around so cut four strips out of that. Drilled three holes in each, located the strips on the shroud and drilled the holes in it. Finally I put it all together with some M4 screws and nyloc nuts. The hardest part of this was getting holes punched in the flaps, the rubber used is pretty tough. When all was said and done, I ended up with this:
It wasn't the prettiest thing I've ever done, but I found cracking on the attachment tabs on the shroud so I wasn’t sure how much more life it had anyway. I doubted anyone would be looking at it that closely in any case given the location of the flaps on the shroud.