Today was the first day I got a tiny bit better. At least I wasn't so sleepy anymore. So, I tried to do a little something on the nav light installation and if it was just to get my mind off that achy stomach.
I trimmed back the fiberglass to the scribe line. I wasn't really sure how to do it. The manual says to use shears within 1/16" of the scribe lines and to sand down the rest. Well, when I tried to use the tin snips on the fiberglass I could immediately see how hard it is to cut a precise line and also that the fiberglass was delaminating around the cut. Both didn't look really appealing to me as either one could mess up the part for good.
What I did was to sand it down entirely with the high speed die grinder. A messy and dusty job but no delaminating and pretty precise too. The last 1/16" or less I sanded down with some 100 grid sandpaper pulled on a 2x4". That worked pretty fast and the result looks good. If anybody has a better idea how to do this with less dust, please let me know.
Having removed the outer brim of the part I fitted it to the wingtip and removed some more material with the sandpaper and then drilled the holes through the outer flange into the wingtip. There's not really a good way of clamping the part to the wingtip as there is no flat surface anywhere that would take a clamping force without slipping off. So I suggest to first drill the hole through the fiberglass part and then holding it firmly in place on the wingtip to drill through the metal. That way it is less likely to slip. Then cleco as you drill along.
After this step, they make you drill into the wingtip closeout and the lower flange of the fiberglass part. Again, cleco as you drill these. The next step that reminded of my old days when I was building RC model airplanes, was to fill the void between the outer flange of the fiberglass inner area and the wingtip with floxed epoxy. You add as much epoxy as required to make it not run from the mixing cup, which means it is practically kneadable. Never add the flox to the resin before you thoroughly mixed the hardener with the resin as the flox will prohibit a good mix.
Unfortunately I didn't have a slower curing epoxy. I was even running to Home Depot to get some 20-minute epoxy only to find that all they had was the quick curing stuff around 5 minutes. To avoid insane HazMat shipping charges on something so simple as a 20-minute epoxy I got another set of bottles of the 5-minute stuff and vowed to just work faster.
So, I prepared everything at the wingtip, applying car wax ahead of time, getting the fiberglass part ready, putting wipes and alcohol next to the wingtip, putting release agent (car wax) on the tips and mechanics of the clecos, etc. Then I mixed the stuff and added the flox. Boy did it cure fast! I barely had enough time to apply it to the outer flange before I could feel the heat coming from the mixing pot. I rushed to the wingtip and put the part in place, pushing hard to squeeze the excess (thick) epoxy out to the sides. The clecos went in and I quickly wiped off the spilled epoxy from the around the wingtip. Wow, just in time. The curing kicked in and I could feel the heat coming from the nav light fairing.
I noticed that I had to do another run as I had applied the epoxy filler only in the region the manual had told me. The far front and aft of the fairing where not touched but I could see a small gap in the front and aft section as well and particularly in the front I didn't want to have that. When riveting that gap will put stress on the fiberglass part and it might crack over time.
So after a while I took the part off, cleaned off the wax in the aft and front areas of the outer flange and prepared for another run. That went on quickly and let the part sit for a couple of hours to let it cure.
Taking it off after that showed that there was way too much epoxy used on the first run. It built up a shelf inside that added a lot of unnecessary weight to the part. When finally cured I will have to sand this off again. Van's said to mix 2-3 fluid ounces of epoxy which I think is way too much. Take it easy and build it up in multiple stages if you really have to. Chances are 1 fluid ounce is sufficient for the whole flange.
That was it. Sounds like a lot happened but everything was done in about an hour.
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