The tank skins need to be final drilled in preparation for assembly. The first task is to final drill the bottom skin to the tank stiffeners. These stiffeners are needed on the bottom skin because the tanks will be holding the weight of 21 gallons of gas. I began by labeling each stiffener to I could later install it in the same location as it was drilled.
Here are all of the stiffeners for one fuel tank.
The skins were then final drilled to the ribs while the ribs were installed using clecos. Next, the blue vinyl was removed along the rivet lines on the tank skins.
The tanks have some additional fittings that need to be drilled. First, the filler flange is match drilled to the skin. This is the internal view of the filler flange with the filler cap installed.
Finally, the drain flange is installed at the lowest point in the tank. This will be used to hold a quick-drain valve that is used to drain fuel samples from the tank and to remove accumulated water in the tanks. The drain flange rivet holes are not pre-drilled in the skin so the builder needs to match drill these holes in the skin using the flange as a guide.
Here are the completed rivet holes for the drain flange.
With all of the drilling completed, it was time to deburr all of the drilled holes and to deburr the edges of the tank skins to remove any jagged irregularities and to leave the edges smooth so they resist cracking. I’ve found that sandpaper on a sanding block is the best way to deburr and smooth skin edges.