Initial Prep (Debur, Trim, Drill, and Cut)
11/3/2021 – 1.2 hours
The wing spar flanges have several holes that were not match-drilled #40 to the J-Channel in the previous step. Those holes need to be final-drilled #40. Most of the holes for nutplate rivets were already sized #40, which greatly reduced the number of holes that actually had to be final drilled.
[#40 Drill]

Final Prep (Dimple, Countersink, and Shape)
11/4/2021 – 2.6 hours
11/5/2021 – 1.7 hours
11/7/2021 – 1.4 hours
11/12/2021 – 2.2 hours
Every hole in the spar flanges, and a handful of holes in the spar web, is countersunk. The trick is that there are 4- different levels of countersinking, and you have to pay attention to countersink each hole correctly. The nutplate and rib holes that will lie underneath the fuel tank skin (inboard forward row) are countersunk for a flush rivet so the fuel tank skin can sit tightly on top of the riveted area. The nutplate holes on the aft edge of the flanges are also countersunk for flush rivets. Those nutplates are for wing access panels. The forward, outboard holes and all of the skin and rib holes in the aft row are countersunk a little deeper (.005” to .010”) for the wing skins that will connect to those holes. Finally, the attach holes in the nutplates are countersunk to the maximum outside and inside diameters specified in the plans for each type of nutplate.

In general, it's a good idea to complete the steps on each sheet in order. In this case, a step near the end of the sheet calls for spot-priming the countersunk holes. This instruction comes after the nutplates are riveted in position, which would make those holes impossible to prime. I decided to do all the countersinking, followed by priming, and then riveting the nutplates into place.

The final countersinking task occurs after the nutplates are attached to the spar flanges. The screw holes for the tank attach and access panel nutplates get enlarged, and the nutplates provide the guidance for the countersink cutter pilot to keep the holes round and concentric. The countersinks are very deep and large, and I spent a lot of time countersinking a scrap piece of aluminum to set up the microstop countersink cutter. My scrap piece was the same thickness as the spar flange (1/16”), which made it convenient to measure both the top (large) countersink max diameter and the bottom (small) countersink max diameter.
[Microstop Countersink Cage, Countersink Cutter with #40 Pilot, Countersink Cutter with #30 Pilot, Palm Drill, Digital Caliper]

Prime
11/8/2021 – 0.9 hours
11/12/2021 – 0.3 hours
Priming (or not) is generally left as a decision for the builder, but the plans for this step instructs the builder to spot prime the areas where the anodized finish on the spar was removed during countersinking. I took a rattle can of primer that didn't spray very well, and sprayed some primer into a paper cup. I then dipped a Q-tip into the primer and used that to prime the countersunk holes. I didn't scuff or clean the holes prior to priming, but I wasn't worried about the primer holding since I'd be filling the areas with anodized rivets. I just wanted enough primer to discourage future corrosion, not necessarily a thick paintable coat.
[Dupli-Color Self-Etching Automotive Primer (Green – Rattle Can), Q-tip, Paper Cup]

Assemble
11/9/2021 – 2.0 hours

11/10/2021 – 2.0 hours
11/11/2021 – 3.5 hours
Several nutplates to attach the fuel tanks and wing access panels are riveted to the top and bottom flanges of the wing spars. The nutplates are easy to access with the pneumatic squeezer, so the real challenge is how to hold the nutplates in place while setting the rivets. I initially started with a cleco in one rivet hole while riveting the other side of the nutplate. That generally worked, but there were a couple instances where I lost sight of the nutplate and damaged it with the squeezer. Those nutplates had to be removed and replaced.

The method that worked best for me was to hold the nutplate in place with a cleco clamp covering the hole for the screw. The clamp held the nutplate tight to the flange for riveting and also protected the nutplate from the squeezer. This probably isn't the fastest method, but I was happy with the results. There are also four nutplates at the outboard end of the spar web to attach. The squeezer can't reach those nutplates, but back-riveting works well for them. The nutplates for the spar web are different than the ones on the flanges, so you need to read the plans carefully!
[Pneumatic Squeezer, Flat Squeezer Set, 3X Rivet Gun, Back-rivet Set, Small Back-rivet Plate]