I am now mostly done with the wingtip fitting following Bullocks write up.
There are a few things I would have done different. For example when cutting off the strip that later is used as a spacer, I would leave more of it on the tip. Right now it is tricky to insert the tip into the wing, it tends to snag the skin edge. I expect it to get worse after painting. It was not an issue when things where clecoed as the assembly had some flexibility in both the wing and top. But when riveted it firms up and the flexibility is much less. There are two ways of solving this:
1. Have basically no material sticking into the wing skin. I don't like that solution, even with the P4 hinge providing I nice, clean backing, the opening would have been too big.
2. Have more ‘flange' material. This will serve both easier insertion and a better looking glass/aluminum transition.
One of the challenges is how precise the cut off is done and how much material to leave for the spacer. It has to have enough material to support countersinking and not to crack during riveting. A very thin cutting blade could accomplish this, but making a separate spacer is another option. It can easily be checked adjusted while having both hinges on the tip and the thickness can be made to match the existing spacer. In best base, the sweet spot found, but I didn't find it:
Unfortunately, I ended up with too little and had to add back material. Trying to shape that edge afterwards was not easy.