Brief Description: Countersink #8 Screw Holes on Top Flange
I was able to finish countersinking all of the rivet holes for the nutplates on the top flanges of both spars. The manual then recommends riveting on the nutplates and then using the nutplates themselves as the pilot for countersinking the #8 screw holes. I was worried about doing this for a couple of different reasons. First, I thought the countersink pilot might bugger up the threads in the nutplates. And second, Van's recommends using the #30 pilot countersink bit. The #30 fits into the nutplates, but it is far too small for the #8 screw. I ended up using my doubler plate again and using the larger #20 pilot that securely fit the #8 hole. This worked well, or so I thought. (Addendum: when I finally riveted on the nutplates on the top flanges, the center holes for the #8 screws didn't line up very well with the corresponding holes in the nutplates. I decided to follow Van's recommendation on the bottom flanges and everything lined up perfectly. And my worries noted abover turned out to be unfounded. To fix the top flanges, I went back with the #30 pilot countersink after the nutplates were riveted on and slightly increased the size of the countersinks which also served to center the holes with the nutplates themselves.)
