Mikhailtech has posted an Antec SX-830 Case Blowhole guide

The next step is to cut the blowhole itself. The cutting disks work very well, but the 2mm cold rolled steel of the Antec case chewed them up very quickly. I went through five disks in cutting the hole. It was after running out of disks that I decided to try and use the carbide cutting bit, much to my chagrin. It is obviously not adept at cutting steel in the manner which I hoped, and I ended up gouging part of the steel outside of the blowhole in the process. After returning from the store with a fresh batch of cutting disks I finished cutting out the blowhole. At this point the hole is very rough and unfinished. The grinding stone becomes very useful at this point in order to shape the hole and remove any metal burs that would like to find their way into your fingers.

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