Shock cord installation was a bit of a comedy.
I decided to anchor the Kevlar on a 20/50 centering ring. The trick is that I needed to push it way far down into the body, from the top end.
First, I filed a notch in the edge and glued in the piece of Kevlar (with a knot at the end). This was just to hold it together while I push it into the tube.
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Then I started to scratch my head figuring out how to get it installed.
I decided that I wanted to push the ring into position from behind, so it would form a natural fillet in front of the ring, in the direction the cord will be pulling it. So I pushed the ring all the way in, past where it needed to be (approximately underneath the front transition). From the front, I pushed with a piece of 3/4" PVC, which worked perfectly. Then I did a practice run pushing from the back. Uh oh. To work around the engine block, I needed to use a smaller-diameter pusher; I grabbed a 3/4" (or maybe 5/8", something like that) dowel. But then I couldn't push the whole ring at once; I'd have to push one edge at a time. This made it very easy to dislodge the ring and leave it cockeyed in the tube. I decided to try it anyway.
I applied epoxy (the inside of the BT was CA-coated, so I wasn't gonna use wood glue here) in a ring inside the tube, in the approximate correct position. I used a long 3/16" dowel, and trying to avoid touching the epoxy blob to the BT while threading the dowel down into the tube was like playing Operation. I eventually got what seemed to be a decent ring of glue there. Now to push the ring into place.
I got my dowel and pushed from behind, working around the edges of the ring. Doing this all by feel was incredibly difficult; so much so that I quickly dislodged the ring again, just like in practice, so it was now sitting at an angle. I could look in the end with a flashlight and see a bit of what was going on in there, fortunately. So then I took my small dowel and slowly pushed on the nearest parts of the ring until it seemed to be lodged symmetrically in the tube. This took a while. Then I looked in the other end with a flashlight to try to make some determination if I had probably landed the ring in the epoxy. I thought I saw some epoxy blobbed up around the edge of the ring, so I assumed I had landed in the correct spot.
Finally I attempted to add a little more epoxy around the perimeter as a fillet. I honestly have no idea if that helped (when working more than 10" away from the end of the tube, it is not easy.)
In the end, I think it's OK. When fully cured I'll test the strength a bit and make sure it stays put.
So it's probably successful but not one of my most well-thought-out bits of building. If I had anchored the cord to a short piece of coupler (or even stacked two centering rings), I could have at least made it so it would stay lodged properly in the BT. That would have saved a *lot* of effort.
Oh well, down to the very end. I also Futured the whole rocket, so the only step remaining is to attache the elastic shock cord and hook on the parachute.