As with the Photon Disruptor, the XC instructions have you build the motor mount early on but not install it until late. I’m not sure why. I can think of a couple of advantages but not necessarily ones the instruction authors had in mind. ((1) If you screw up the fins, etc., at least you still have a motor mount you can use on your next attempt, or on a different rocket altogether (2) Like Chris Michielssen, you can wait until late in the build to change your mind and use a larger diameter motor mount than the kit’s.) As pointed out earlier, though, by installing the motor mount late you have the possibility of distorting the fin angles if the body tube’s out of round. Also, my rocket rotisserie relies on the presence of a motor mount to work.
But you know what? You can have your cake and eat it. Dry fit the mount into the body tube! Problem solved.
On goes the first fin.
Here are two more fins in place. I did the two wing fins first, then the bottom fin. I figured it’d be easier to get the latter at the correct angle if both wings were in place first.
I had a thought, which if it doesn’t work out, I’ll be sure not to tell you about. But it led me to hold off on the top fin for the time being. Instead I pressed onward to start the really fun part: Cutting the tubes.
I took a spare bit of BT-50 and built it up with some blue tape for a snug fit inside the tubes to be cut. That strengthened to tube end to reduce deformation while I was trying to cut it. I loaded up the knife with a nearly-new blade — a little later I swapped it for a brand new one — and made the curved end cut. Then the two lengthwise cuts.