Going around the inside of the G, you'll notice that I made a second pilot hole, but this one wasn't to feed the blade through.  I wanted it there for a place where I could turn the piece around without doing any cutting.  If you rush things or attack from the wrong angle in delicate areas, you can break or cut through parts you want to keep.  Good thing I didn't do any of that!

On the last small part to cut, part of it is only as wide as the blade itself, so making that area the meeting point for both sides works well.  The thinnest gap should fit a small piece of sandpaper just fine, or a small flat needle file to clean up the edges.

Cutting's done, lets take it outside to have a quick look before we remove the tape... not too bad!

Back inside I removed the tape and admired my work.

With a blue background, you can see some of the smaller mistakes which can be cleaned up during the sanding and filing phase.

Here's another design I did with this technique, x24's winning submission for the Fan Grill Contest.

It seemed like I was able to get the edges smoother and cleaner where curves were used, and this one won the contest because it seemed like it would fit in well with the designs of most cases.  Merlinicorpus's design also turned out well, but looks slightly unfinished, which might not mesh with some mods.  Now, one more design, one I thought would fit well with the acrylic's color.  I Googled for an image of the Radiation symbol and printed it out like the other two, and used the outline from AC Ryan's MeshX fan grill to make the outline.

With some time and an idea, you should be able to make some of the fan grills that appear in your projects on your own.