I have noticed that if you follow the standard process for hole prep (drill to #40, "lightly debur," and dimple) that the rivet is not snug in the hole.  The dimpling actually stretches the aluminum and opens the hole leaving the rivet somewhat loose.

 

I went to far as to perform a quick test.  I took 2 pcs of scrap, drilled, deburred, dimpled both pcs, and riveted them together.  I then cut through the center of the deformed rivet so as to have a crossection of the riveted area.  I cleaned it up with some sandpaper and a Scotch Brite pad.  Looking at the crossection under a magnifying glass, I could see that the rivet deformed to the point where is pretty much filled in all of the space and minor voids created by drilling and dimpling vs dimpling & drilling.

 

However, with that being said.  I took the advise of an RV-4 builder and moved up to a #41 drill bite (#40 = 0.098" #41 = 0.096").  This makes a noticable difference and leaves a nice tight dimpled hole.

 

LEARNING: Order #41 drill bits and use them whenever you would use a #40 and dimple.

I have been doing a lot, and I mean a lot, of edge finishing.  I have been using a file to round corners, 120 Emory cloth, followed by a Scotch Brite pad.  All by hand.  The edges are as smooth as a baby's bottom.  I'm sure that I am doing more than I probably need to, but I feel that stress risers and crack propegation is the most likely longer term problem with aluminum airplanes.

 

For some time now, I've been thinking of getting a Scotch Brite wheel.  Recently, I was talking with an RV4 builder who told me, in a polite way, that I was stupid for doing all of the deburring by hand and that I needed to buy a SB wheel.  He even gave me a little demo using the SB wheel in his hanger.  So I bought a Ryobi ginder from Home Depot, removed the wheel housing from it, and ordered a SB Wheel.  I've been told that a single wheel can get you through an entire airplane.

 

Well, I've added the SB wheel to my arsinal of metal finishing tools.  I'm actually mixed.  It definately helps, but IMHO, there is no substitution for hand finishing.

 

LEARNING: It's worthwhile to invest in a Scotch Brite wheel, but it's not the be all to end all.

You quickly learn that there is a lot of deburring, sanding, and scotch briting required to get the parts ready for priming and/or assembly. This can lead to your hands becoming rather gray/black from the aluminum dust.  I have found that latex gloves come in real handy.

 

LEARNING: A box of 100 latex gloves for $8 from Home Depot is a worthwhile investment.

One of the tools that I purchased was a low end band saw from SEARS.  I comes with a 6 Teeth Per Inch blade.  I purchased a few extra blades, a 15 TPI and an 18 TPI thinking that the 6TPI blade would result in too rough of a cut.  As it turned out, the new blades didn't cut very well at all.  So I put the 6 TPI blade back on and it cut through the aluminum attach angle stock much more easily.  I was discussing this with a buddy at work, and he has had the same experience.  This is generally contrary to what is supposed to happen.  I have one other theory as to why this may be but it would take too long to explain it here.

LEARNING: The 6 TPI blade works just fine for cutting the aluminum angle!