Cowl corner filling

So, with the hinges taken care of, I decided that my next step would be working on finalizing the hinge pin cover cutouts. Previously, I rough-cut these, and sanded the lower cowl cutouts to fit the cover, but I needed the hinges in place before I could put the cowl halves together and work in finishing the upper half of the cutout.

At first I started gradually opening up one of the cutouts, and got fairly close to getting the cover to fit, but then I started looking more closely at the front cowl corners. There were two issues here that I felt needed to be remedied before finalizing the cutouts. First, the upper and lower cowl halves were making contact here, especially on the right side, when there should be a bit of a gap there (for paint). Second, the previous misalignment between the halves was still there, particularly in the area leading right up to the cover cutouts. It seemed counterproductive to carefully work on those cutouts and then slap some filler in the area.

So I switched gears – first, I worked on reopening a minimal gap between the halves in the corner area, then I switched to working on the filling. First task before filling was to do some more rough-sanding of the last micro application. For one thing, I needed a relatively even surface to put more micro on top of, but I also wanted to sand roughly to the lower corner contour so I could have a better idea of where I needed to build things up.

The latter turned out to be a good idea – once I’d sanded roughly to match, I could see that the contour leading up to the corner os each air inlet was a little funky looking. Basically, the area near the split was built up to match, but moving upward from the split, there was a pretty obvious slope back to the original contour, which looked a little funky. So I decided that this next application would cover more area vertically, to provide a better chance for contouring things.

I also decided to put in some flox inside the lower corners. Doing this gives me some structural filler, so if I decide I want to sand back the lower cowl a bit, I’ll have more room to work down there without worrying about thinning things out too much. But before getting to that, I made up some forming aids. Last time, adding the micro was tough, since I wanted enough excess protruding beyond the cowl cut line to allow me to sand it back to a nice flat profile, but that also made getting a good buildup tough. This time, I took some scrap posterboard type material and covered it in packing tape. The idea was to pin the cowl covers together for this work, and trap the posterboard between the two, thus giving a nice flat edge for the flox/micro to “mold” against.

I did the flox layup first. I think I could have added more flox to the epoxy; it seemed stiff in the cup, but kept wanting to sag after I’d applied it. The taped-up cards came in handy here; in order to address the sag issues, I flipped the lower cowl upside down, with the cards under the corners, trapped against the work table. This way the flox mixture was sagging into the joint, not out of it. I left the cowl like this for about 45 minutes, which gave the mixture some time to set up; after that, the sagging wasn’t a problem any more, but the epoxy was still malleable enough that I was able to shape it the way I wanted, before pinning the cowl halves together again, with the cards in place. I ended up flipping the assembly upside down just in case I got any more sag.

A few hours later, once I was confident the flox was definitely cured enough to not sag, I flipped the cowl again and started working on the micro. I drew a reference line on each card, to give me an idea of about how far out I wanted to build with micro. Then I started by using a small popsicle stick to work the micro mixture into the “corner” formed between the cowling and the cards – I figured this would be a likely spot to create a void if I wan’t careful. Then I worked on just slapping on more micro and trying my best to same it into reasonable shape.

As is always the case, the end result looked pretty crappy at first, but instead of focusing on trying to make it super smooth, I instead focused on trying to get rid of any potential voids from trapped air. Then I let the micro cure or about half an hour – like with the flox, I came back out and massaged it into a more pleasing shape while it was still malleable.

Still looked kinda crappy, but the card confined it nicely:

After waiting another couple hours for the micro to firm up, I pulled the halves apart and got the card out of there. This time I definitely got plenty of micro in place…I don’t think I’ll run into the problem of not having enough material to sand down to the right contour. Instead, it’ll be having to sand a lot off:

I actually got a head start on the sanding tonight. Since the micro was stiff, but not super hard, I tried shaping it with a Surform tool, kind of like you might do with Bondo. It worked pretty well, and while there will still be plenty of sanding, I at least took off a fair amount of material and got a head start.

Tomorrow: sanding time, HOORAY!

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