Hard to demonstrate the technique on video because a lot of it has to do with how much pressure you apply. I'll give it a shot, maybe when I'm back from our vacay.
I'll start with the disclaimer - you can f**k yourself up if you are not very careful! I work outside, wear safety glasses, hearing protection, and a dust mask. Some aluminum does actually get airborne. There is a reason that is not good for you to inhale it, but my short term memory loss seems to be prohibiting me from remembering why...
It's not a bad idea to wear leather gloves too. Make sure they fit snug like mechanic's gloves so they wont catch if the spinning brush hits your hand.
Basically I hold the drill with the spinning brush (fine bristles about 3-4" diameter) with two hands at a 45 degree angle to the sides of the plate, and get an even finish over the whole plate except the two opposing corners that I clamp to the work surface. Don't need a ton of pressure and it is hugely beneficial to make sure the plate is grease free before you start. Contrary to what PB says I do find that going over a spot several times starts to eat into the finish and make a spot that looks more worked than the rest of the surface. Once I have the even finish I turn the wheel to 135 degrees (the "other" 45 degrees relative to the edge of the plate). Then I just sort of randomly wiggle the drill and let it sort of bounce lightly off the surface to generate contrasting marks 90 at right angles to the base pattern. Then release one corner clamp and carefully brush it to match. Release the last corner, hold the drill in one hand and hold the panel with the other and very carefully brush the final corner.
Be VERY careful, particularly along the edges where the brush wants to catch on the edge of the panel. In fact I will say just don't do it if you have any doubts. The ability to safely control hand held spinning motor tools is something a person needs to make their own decision about attempting.
