Brief Description: Deburr Skin and Start Countersinking
I finally got some time after work to do something on the fuel tank. I finished the deburring of the skin edges, cap and drain fitting holes. It took a bit of time because of the large nubs on one edge of the skin from cutting off the splice strip for the OB LE.
The plans call for having the baffle plate and stiffener temporarily installed to countersink the holes in the skin common to the baffle plate. The skin is only 0.032 inch thick and countersinking for a 426AD3 rivet will leave a knife edge. I think they want to do it this way instead of dimpling because joining two flat surfaces will give a better opportunity for proper sealing. I've read that the majority of leaks are in the baffle sealing.
The plans also have a note that it's better to have up to 0.005 inch shallow countersinks than to be underflush by any amount. That's because the knife edge you create will enlarge the hole. Using some scrap 0.032 in. material I tested several different countersink depths from flush to 0.005 in. shallow to see what the knife edge looks like. At flush, there is a sharp knife edge bot no hole enlargement. I could see a very slight bearing surface at 0.001 inch shallow, and a rivet in a 0.003 in. shallow countersink sat a bit to proud. I settled on 0.002 in. as a good compromise.
I got the cage set for 0.002 in. but ran out of time for the day before I could start countersinking.
Stiffener and baffle temporarily installed for countersinking baffle fastener holes
