Building the Shrockets Sea Sting (part 3)

Yikes.IMG_3162The scoop tube had been stretching out a good while, it was stable at about the right size… and the glassine layer was bubbling up away from the cardboard. (That’s just geometry. The area of the outside of a tube is larger than the area of the inside — but if you flatten it out completely the areas of the two sides are the same, and partially flattened out the outside is larger but not by as much as when it was a tube. So the area of the glassine is “too large” for this shape, and it gathers up into these bubbles. Well, it’s geometry plus materials properties — if the glassine were stretchier, or more firmly adhered to the next layer, it wouldn’t do this.)

Perhaps it would have been all right if I hadn’t over-stretched it? I was afraid I wouldn’t be able to get it glued on unless it was stretched open to make the gap close to the right size, and to make that happen I put it around a jar large enough to stretch it past that point, so it would spring back to about the right gap size when I removed it. Maybe I shouldn’t have. But I’m just not sure I could have made it work if I hadn’t.

How to fix it? I tried sanding it down with 220 grit and that helped a little bit. Would filler primer and sanding will take care of everything? I gave that a try but wasn’t happy. Really it required sanding right through the bubbles, but that left a very messy surface.

I found that with some care — generally using a knife to lift an acute corner at one edge, and working from there — I could peel almost all the glassine off, with not too much collateral damage to the underlying layer (which was not bubbling). What I couldn’t peel I could sand down.IMG_3191 It’s ugly, but now the irregularities are concave, not convex. Some CWF in the spirals and maybe a couple other places, some filler primer, some sanding, and it should be okay.

I sanded down the nose cone seam — nothing seemed to need filling, fortunately —and roughed up the rest of the surface. Primed it with Krylon plastic primer then Rustoleum filler primer for a consistent undercoat with the body. (Mixing brands, but it worked.) (Why, yes, I am cutting and pasting from one build thread to another. Why do you ask?) I primed, then color painted the scoop area of the body tube and the scoop fin — all masked to keep paint off the edges to be glued. IMG_3192 Since most of this area will be barely visible I didn’t spend too much time on it and am not worried about how bad the spirals look. But they’re going to have to be taken care of for the more visible parts of the model. Ah, my favorite part of rocket building. </sarcasm>IMG_3194

 

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