I have a cas w/ 2 80mm holes in the front. I want to take one of those holes and make it larger....by about 40cm, so that I can hang a 120mm fan in there. I read on one of the recent threads that I should go for a 114cm hole bit on a drill. I'm hoping that like, I cold dothis without a 'hole' bit..and maybe just a saw. What do you guys think?