1/17/2021 -- 5.6 hours
This was a deceptively easy-looking step on paper, but execution takes a lot longer. I started by removing the blue vinyl from the two HS skins and deburring the edges. I used a 3M wet/dry sandpaper product for the initial deburring that worked really well to remove the tooling marks from the edges. I then followed up with an edge-deburring tool and a final light pass with the sandpaper. With the edges deburred and the “no-dimple” holes marked, I moved on to dimpling. Each skin has 400+ holes to dimple, so this takes awhile! I finished dimpling one skin, which was enough for one day. A complicating factor in this step is the fact that the continuous skin that is pre-formed at the leading edge leads to very awkward access to the holes with the C-Frame and some close-quarters holes toward the leading edge. A second set of hands to hold the skin out of the way would be ideal, but the family was out of town and I was working solo. I compensated by using three strips of duct tape and folded towels to hold the opposite skin back so I could dimple effectively. That worked really well, and I will do that again on the second skin. I also had my first major dimple disaster. I didn't notice the dimple die had slipped out of the hole when I was wrestling with the skin (before I came up with the duct tape / towel idea), and I ended up puncturing the skin right next to the hole I was supposed to dimple. I “undimpled” the error with a flat set, deburred the hole I made and radiused it where it intersected the hole I was supposed to dimple, and dimpled the correct hole. Deburring and removing the sharp corners from the unintended hole should mitigate future cracking issues in this area, and the hole will end up beneath the fuselage fairing so there is no real cosmetic issue. I'll let me tech counselor take a look to see if I need to do anything else with this error. Lesson-learned…
[Edge Deburring Tool, Sandpaper, Scotch Brite Flap Wheel, C-Frame, 3/32 Standard Dimple Dies]
1/18/2021 – 4.6 hours
Another nice day means another opportunity to prime parts! It was a bit windy, but I managed to get all of the HS skeleton parts prepped and primed. It looks like the weather this weekend will be nice, too; so I'll get the HS skins prepped and primed then. With the priming out of the way, I returned to dimpling the HS skins. This continued the process of the previous work session, and almost all of the holes were dimpled successfully. The most forward holes are too tight for access with the C-Frame, so I'll get those in the next session with a close-quarters dimple die.
[Grey Scotch Brite Pad, Bon Ami Cleanser, Dupli-Color Self-Etching Automotive Primer (Green – Rattle Can), C-Frame, 3/32 Standard Dimple Dies]
1/20/2021 – 1.3 hours
The C-Frame cannot access the forward-most holes in the horizontal stabilizer skins, so I had to go to my 3/32 Close Quarters dimple die set. I only used this dimple die set once before on my practice project with mediocre results, so I was not anxious to use it on the HS skins. The Close Quarters dimple dies have a hole in the center for a mandrel (aka nail), and the mandrel is inserted into a blind rivet puller to apply the pressure to form the dimple. The idea is to put enough pressure on the die to have them contact the skin, but it is not necessary to use so much force that the mandrel breaks. I very patiently squeezed the Close Quarter dimpler on each of the 16 forward most HS holes, and I was pleasantly surprised with the very good results. The dimples are not quite as well formed as the ones created with the C-frame, but they are more than acceptable to seat the flush rivets. Definitely a win!
[Close Quarters 3/32 Dimple Die Set, Blind Rivet (pop) puller, Nails]
1/21/2021 – 2.0 hours
The countersinking process began with the horizontal stabilizer forward spar. I clamped the HS forward spar to my work bench, and countersank all of the #40 holes in the flanges (top and bottom) to receive .025” thick dimpled skins. I have a small piece of .025” aluminum with #30 and #40 dimpled holes that I used as a template to set the depth of the countersink cage. I found that setting the countersink cage .009” (9 clicks) beyond flush gave the correct depth to hold the dimple firmly without any play and allow the skin to sit flush against the spar. I countersank all of the holes on the top flange of the spar, then flipped it over and re-clamped it to couintersink the holes on the bottom flange.
[Air Drill, Microstop Countersink Cage, 3/32” 3-Flute Countersink Cutter, Clamps)
1/22/2021 – 1.9 hours
This section concluded by countersinking all of the #40 holes in the top and bottom flanges of the aft spar and the #40 holes in the stringers. I reset the countersink cutter to .009” beyond flush, clamped the spar to the workbench, and countersunk the holes from the center of the spar out to the ends. Countersinking the stringers was similar, but I could not easily clamp the stringers down. Instead, I put a scrap of wood under the stringer flange and clamped that to the bench. The stringers are much shorter than the spars, so countersinking went pretty quickly.
[Air Drill, Microstop Countersink Cage, 3/32” 3-Flute Countersink Cutter, Clamps)