For lack of a #6 nutplate jig, to locate the nutplates, I used a K1000-06 nutplate with an AN507-6R6 screw inserted backwards. Inserting this into the #27 hole with a cleco-jaw, match-drilling one side, then holding it down with a cleco, permitted me to get these guys properly placed.
Turns out countersinking Fiberglas isn't so easy. Using a cutter in a cage is challenging since it's hard to keep it flush given the inboard bevel on the wing tip and the part's flex can ruin the depth of the countersink. So as an alternative, I manually did all rivet countersinks with a free cutter. When doing the screw hole countersinks I noticed some chattering around the edges so I switched to a zero flute countersink. It made nicer countersinks and I used it entirely on the right tip, utilizing a block of wood on the tip underside to mitigate flexing of the body.
Here's a comparison between an untouched rivet (left) and one that was inserted and removed several hundred times into Fiberglas (for proper countersink sizing). Notice anything missing?
I decided to use "soft" rivets to mitigate cracking of the Fiberglas. This is given as an option in the plans. So I used AN426A3-4 rivets. I calibrated my squeezer against some scrap Fiberglas from the wing tip cutting essentially listening to when I could hear the cracking, and backing off several turns of the squeezer's piston for the final setting. The rightmost squeezed rivet below did not damage the Fiberglas.
Turns out this isn't the way to calibrate things as the nutplate takes some of the expansion pressure. So here's what the nutplate rivets ultimately looked like.
Putting on the nutplates was uneventful. As I was solo on this, I needed something to "work against" when squeezing the rivets, so I propped up the tip body with wood blocks as I moved down the tip's length.
However, after the nutplates were on, it was clear that the lack of a pilot on the zero flute allowed the countersink to be off-center of the holes. This was a much bigger problem with the #27 holes for the AN507-6R6 screws than for the #40 rivet holes. I needed to take a different approach on the left wing tip. So on the left tip, I first countersunk for the nutplate rivets, installed the nutplates, then used a #40 cutter to countersink for the screws, using the nutplate as a self-centering guide. It worked much better than the approach I took on the right tip.
Turns out countersinking Fiberglas isn't so easy. Using a cutter in a cage is challenging since it's hard to keep it flush given the inboard bevel on the wing tip and the part's flex can ruin the depth of the countersink. So as an alternative, I manually did all rivet countersinks with a free cutter. When doing the screw hole countersinks I noticed some chattering around the edges so I switched to a zero flute countersink. It made nicer countersinks and I used it entirely on the right tip, utilizing a block of wood on the tip underside to mitigate flexing of the body.
Here's a comparison between an untouched rivet (left) and one that was inserted and removed several hundred times into Fiberglas (for proper countersink sizing). Notice anything missing?
I decided to use "soft" rivets to mitigate cracking of the Fiberglas. This is given as an option in the plans. So I used AN426A3-4 rivets. I calibrated my squeezer against some scrap Fiberglas from the wing tip cutting essentially listening to when I could hear the cracking, and backing off several turns of the squeezer's piston for the final setting. The rightmost squeezed rivet below did not damage the Fiberglas.
Turns out this isn't the way to calibrate things as the nutplate takes some of the expansion pressure. So here's what the nutplate rivets ultimately looked like.
Putting on the nutplates was uneventful. As I was solo on this, I needed something to "work against" when squeezing the rivets, so I propped up the tip body with wood blocks as I moved down the tip's length.
However, after the nutplates were on, it was clear that the lack of a pilot on the zero flute allowed the countersink to be off-center of the holes. This was a much bigger problem with the #27 holes for the AN507-6R6 screws than for the #40 rivet holes. I needed to take a different approach on the left wing tip. So on the left tip, I first countersunk for the nutplate rivets, installed the nutplates, then used a #40 cutter to countersink for the screws, using the nutplate as a self-centering guide. It worked much better than the approach I took on the right tip.
Here is the right tip's bottom side with nutplates installed and screw holes countersunk.
If I were to do this again (oh boy) I would do the following (Update 21-May-20: Turns out, nearly seven years later, I ended up doing it again): After match-drilling #40 the tips to the wing skins, match drill up to #30, cleco'ing as you go. This way, when you go to enlarge the holes on the tips to a #27, the chance for chipping the gelcoat is much reduced and the holes will remain well-centered to the original location. I had a lot of chipping and some of the hole centers moved. Left pic shows a flake of gelcoat torn off when the hole was upsized to a #27. Right side shows how much of the countersink overlapped that.
Next is locating and installing the tip ribs. Time for a build break. I grow fatigued of my airplane.
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