Smoothed the edges and surfaces of the rear spar reinforcement bars to a satin finish equivalent to that left by 400 grit wet/dry sandpaper. Both reinforcement bars required extra sanding to remove deep marks. Clecod the reinforcement bars to the spar channels and final drilled all holes to #30. Oddly, my RV tool kit had #19 drills, not #21. Since the plans set calls for #21, I'll need to procure #21 drills so I can final drill the holes where the main ribs attach to the rear spar assembly.
Stopped by the local paint supplier, English Color and Supply, to pick up a can of R-M Aero Max AM700 self-etching primer. As for the aluminum prep treatment/cleaner, I'm still undecided between the Advantage wax and grease remover (Naptha) at $13.40 a gallon and Chemfil DX 533 at 32.06 a gallon The DX 533 is mixed with water at a ratio of 1:3 so that actually makes it a little cheaper and will last longer. The DX 533, made by PPG, is specifically for aluminum and is used at Air Tractor in Olney, TX.