Initial Prep (Debur, Trim, Drill, and Cut)
4/7/24 – 3.0h
This step is all about preparing the cover ribs that attach to the forward side of the forward center section bulkhead. I waited to start this step until the replacements for my laser-cut cover ribs arrived from Vans. Vans recommended replacement of the cover ribs since the center two ribs on both the left and right sides of the airplane support the control sticks, which means lots of cycles and additional loads.
[Hole and Edge Deburring Tools]

Final Prep (Dimple, Countersink, and Shape)
4/7/24 – 0.5h
One cover rib each on the left and right side is prepared a little differently than the other six. The different cover ribs have three nutplates on the top flange, and are used to mount the bearing brackets built in the previous step. Most of the #40 holes in the top, forward, and bottom flanges of all eight cover ribs are dimpled, and the holes that are not are clearly marked in the plans drawing.

The top flange of the left and right cover ribs that are different from the rest have two #19 holes that are drilled #17 and dimpled for.a #8 screw. Due to the large dimples in the top flanges of these two ribs, a relatively small forward flange near the bottom of the cover rib, and the close proximity of several #40 holes, I went with a reduced diameter #40 dimple die. The reduced diameter cleared the large dimples, small flanges, and adjacent close holes, and is definitely the way to go to avoid damaging the part.
Pneumatic Drill, #17 Drill Bit, Pneumatic Squeezer, #8 Screw Dimple Die, #40 Reduced Diameter Dimple Die]

Prime
4/7/24 – 0.6h
4/8/24 – 0.5h
4/10/24 – 0.5h
[Grey Scotchbrite Pads, Bon-Ami Cleanser, Dupli-Color Degreaser, Rust-Oleum Automotive Self Etching Primer (Green – Rattle Can)]

Assemble
4/10/24 – 1.7h
4/19/24 – 0.4h
This step doesn't have much in the way of assembly - attach a few nut-plates and a couple bearing brackets to the cover ribs. There are, however, some assembly considerations during this step.

First, the top flange of each cover rib gets nutplates attached. Most cover ribs get two nutplates - one near the forward end of the flange and one near the aft end of the flange. Two cover ribs get three nutplates, which are different than the ones used on the other cover ribs and are relatively close together. For these cover ribs, I started with the nutplate in the center, then moved to the forward and aft nutplates. Pay attention to the rivet specs, the length changes depending on the nutplate that is getting attached. I found the pneumatic squeezer with a short yoke did a really good job setting the rivets on the all the nutplates on all of the cover ribs.

The second assembly step is to rivet the bearing brackets to the cover ribs with the 3 nutplates on the top flange. I switched to a longer 3” yoke to provide better access to the rivets, and used the pneumatic squeezer to set these rivets, too. The rivets are long (AN426AD4-8) because the bearing brackets are relatively thick. I had to use thin squeezer sets to give the pneumatic squeezer enough clearance to set the rivets. Another option that I used on the second bearing bracket was to back rivet the bearing assembly to the cover rib. That also worked really well, but one rivet still had to be squeezed because it is just too close to the two adjacent rivets for the back rivet set to fit.

The thing that jumped out at me during this process is the large number of AD4 rivets used to attach bearing brackets to one left and one right cover rib. There are a total of eight rivets that are closely spaced on this fairly small part. The bearings will support the control sticks, and need to be strong to avoid a control issue in flight. Given the loads and loading frequency on the bearing brackets, braces, and cover ribs; it makes sense that these parts are made from thick pieces of aluminum, anchored with lots of rivets and screws to multiple cover ribs and the bulkhead, and that Vans replaced the laser cut cover ribs with punched parts to avoid potential part cracking and failure issues.
[Pneumatic Squeezer, 1” Yoke, 3” Yoke, Flat Squeezer Sets, Small Back Rivet Plate, 3x Rivet Gun, Back Rivet Set, #19 Drill]