I've been modifying cases for quite some time, and I'm getting annoyed with all the Dremel this and Dremel that on the hardware sites.  Dremel tools are overkill for many case modifications.  They're noisy, messy, inconvenient (you often have to gut the computer before you can cut the case) and most of all, dremel tools are EXPENSIVE!

I prefer the more elegant (if you can call it that) approach...the nibbler.  Nibblers are relatively cheap ($10) and can often be used without taking all the components out of your machine.  This particular nibbler is available at your local Tandy/Radio Shack store.  As you can see, the nibbler has a small tooth-like head with an overhang.  When you squeeze the handle, the head is retracted, shearing off a small strip of metal.  The clipping comes out of a channel underneath the head.  The down side of the nibbler is that you need a drill to make a hole to insert the head...but there are a lot of people with drills, so you can probably just borrow one.

So let's gather our stuff together and give this a try, shall we? Since I already have PLENTY of fans in my cases, I'm just going to use a plain old piece of sheet metal...after all, I'm only demonstrating the NIBBLER.

One thing you'll notice if you try to trace out a circle using the fan...the blades get in the way.  I just grab the closest thing that's the same size (I'm lazy).  In this case I used a can.  Of course none of that has ANYTHING to do with the nibbler...but I figured it was worth mentioning.

Once you've got the circle (or whatever shape) drawn, you'll need to drill a hole so you can push the head of the nibbler through the piece of metal.  With the Radio shack nibbler, it requires a 3/8inch hole...that's around 9mm, but you probably shouldn't shoot your case to make the hole ;)

Once you've got a hole (in the piece of metal) just insert the head of the nibbler (into the hole in the piece of metal) and start nibbling

Each squeeze of the handle cuts about 1/8 inch, so it only takes a few minutes to finish up the hole.  The nibbler is best suited to cutting out holes with squared off sides, but a 2 or 3inch (50-80mm) hole is no problem.

Dremel tools leave metal filings everywhere.  The nibbler just leaves these little clippings.  Here's a closeup.

*PRESTO*, you're done. Generally there's no need to sand or file down the edges after you're finished cutting.  The nibbler makes a pretty clean cut.  The clippings are easier to clean up too...they all fall outside the case.  That's why I like the nibbler (that and the fact that they're cheap)

Of course, there is a down side to having a nibbler...they're addictive! For the first week that I had it, I nibbled anything I could.  Pennies, bottle caps, aluminum cans, backplane tabs, dead motherboard PCB's, AOL CD's...you name it, I nibbled it.  I'm going to go to Nibblers Anonymous next tuesday