Aircraft aluminum sheets (as obtained from the kit manufacturer) are usually covered with a plastic coating (our RV-7A was coated with a blue film and the Murphy Elite with a transparent film). This film should be left on for as long as possible during the assembly and construction of the aircraft.
This sheet will prevent the aluminum from being scratched due to handling. Below the plastic film is a very thin layer of pure aluminum called Alclad, helping the sheet to withstand corrosion.
After selecting the correct rivet and drilling the holes, these holes must be prepared and have the burrs removed. This leaves a clean hole without sharp edges and enables a good and proper installation of the rivet or bolt.
Although methods of bonding aircraft structures and skins together are coming into greater usage, riveting is still the most common way of joining parts together. Good riveting will result in a light, strong and effective joint.
There are basically two types of rivets: AVEX rivets and solid rivets. A blind AVEX rivet consist of two parts: the rivet body and, inside, the setting mandrel. The rivet body is inserted in a hole in the structure to be joined, the tool is actuated and the jaws of the pneumatic operated or manual rivet tool grips the mandrel of the rivet pulling the mandrel into the rivet body, thereby expanding it, and forming a strong, tight, reliable joint. And while pulling, the mandrel will break at a predetermined force (set by the manufacturer of the rivet) and falls away, see figure.
Keep in mind to press the rivet tool (with rivet) against the materials to be joined or else the rivet will set with a slight gap from the material. You must then remove this rivet and install a new one.
When selecting the correct rivet, important when doing repairs, is to keep the proper edge distance when the next larger rivet size must be used. If this happens make sure to keep the edge distance for flush rivets at 2 1/2 D and others at 2D. Do not exceed 4 times the diameter.
Rivet spacing is as equally important, generally spacing is kept between 6 to 8 times the rivet shank diameter, just keep it in between 3D and 10D.
To maintain a neat rivet space (or bolt space distance) you can use a rivet spacer. These are very handy and well worth the investment.
Should you ever need to remove a rivet use a sharp drill with a size slightly less than the rivet size so that when drilling through the head of the rivet you do not enlarge the hole. If this should happen, continue drilling but use the next larger rivet.
Usually when a hole is drilled the edges are sharp and burrs are present. Holes can be deburred with a deburring tool or a drill bit of a larger size than the hole being deburred - BY HAND ONLY, NOT IN A DRILL! Simply put the drill bit into the hole and twist just enough (usually one or two rotations) to remove the burr only. Don't go too deep. See figure below.
A cordless screwdriver with a drill bit installed will speed things up here, but be careful not to over do it! With the swivel deburring tool, insert tool into hole and turn once. Generally the tool only deburrs one side, so you may have to repeat it for the opposite side.
All edges should be filed to remove shear or tin snip marks then have the corners 'chamfered', as shown below, with a file.
All flange ends should have corners rounded or at least be cut at 45 degrees, then filed. See drawing below.
Should always have the largest possible radius in the corner as shown below. You can use a circle template to mark out the radius and then use a file to finish it.
After deburring you can use a Scotch Brite pad (purple) to smooth the part and prepare it for primer. Clean thoroughly with Acetone and do not touch with your bare hands, this keeps the parts clean before you spray on the primer.