The orientation of the aluminum stock on the acrylic jig is pretty important if you're planning on doing any detailed shaping around the openings. With this piece, the four holes that accommodate the factory climate controls will be left flat, but the opening for the monitor will be getting a 11/42" chamfer all the way down to the edge. To accomplish this, the aluminum will be placed facedown. In other words, I want the back of the jig facing me and the front of the aluminum facing the table. Adhere automotive body-side molding tape (3M or Kent works very well) to the appropriate side of the acrylic jig so the aluminum can be temporarily attached for cutting with the router. Make sure any thin walls (such as the small, thin span at the bottom of this jig) have tape on them.
This cut should also be performed using the method described above. Although the chamfer is not removing as much material, the final cut (which will need to be sanded and polished) will come out better if the bit and piece are lubricated. It's a good idea to step the chamfer bit up over three or four cuts, say 11/48" at a time, so the bit is not having to work so hard by removing a large quantity of material in one pass.
In order to create a brushed finish, stick the piece to a worktable using a couple of pieces of double-sided tape and use 180-grit sandpaper on a block to go back and forth horizontally across the face of the piece. It will take some time and some practice to get a perfectly horizontal and parallel set of lines, but the end result is a very nice finish, so it's worth the effort. A longer block that will cover the whole piece in one pass is much more effective than a small block as is shown here.
Other examples of aluminum trim work.
After cutting on the router and being wiped down, the piece looks like this. It's a good idea to leave the jig attached until all sanding and polishing is complete for the added strength and thickness it provides. The chamfer will need to be hand-sanded up to 600-grit for a nice finish, starting with 80-grit paper and working through 120-, 180-, 220-, 320- and 400-grit paper in that order. This will remove all machining marks and sanding scratches and get the chamfer ready to be polished.
As mentioned before, I'm going to add a 11/42" chamfer around the monitor opening on this piece. Again, an inverted table-mounted router is the best tool for the job.
You'll need to equip a die-grinder (typically used with a cutoff wheel) with a polishing wheel to take the aluminum from 600-grit smoothness to a chrome-like shine. Blue jeweler's rouge (which comes in a block) works perfectly for this. Simply dig the polishing wheel into the block of rouge to embed the material in the polishing wheel and then apply it to the chamfer, making sure the rotation of the wheel is always away from the face of the piece. If the wheel is spinning in the other direction (toward you) it will catch the edge of the chamfer and throw the piece up and out of your hands. The edge of the chamfer can also be damaged in this way. The polishing process takes a little practice, but it's not too difficult to get the hang of. It's no different than polishing acrylic in the same fashion.
Here's the finished piece installed in the vehicle. A matching piece was fabricated using the same techniques to trim out the track-pad and iPod dock that are located in the ashtray location, as well as the top of the shift knob, lending a unified look to the entire dash area that follows the theme set by the OEM brushed aluminum trim found throughout the interior.