Had a nice amount of time this weekend to work on my build and go through the pictures. As I mentioned, I put in the delrin rail buttons before inserting the fin can. The rear rail hole was drilled 1 cm forward of where the rear centering ring will be when the fin can is inserted. The forward rail hole was drilled as close to the CG as possible. That put it around 2.5" down from the top of the body tube. However, that would put it through a coupler, so that won't work. I moved the drill spot down to 4" from the front. Holes were drilled and reinforced with thin CA. After insertion, a #10 nut was threaded on to the screw and permanently attached with epoxy.
Pic of the front rail button screw with epoxy. Note, the drips you see are the thin CA I used to harder the ends of the body tube. I put it all on too thick, so it ran and had to be sanded down a little to get the couplers to fit. Next time, I'm going to use a wood lacquer that brushes on, soaks in, and hardens like a rock. Should give me cleaner results. I'll save the pricier CA to harden screw holes.
The drogue shock cord was tied off to the eyebolt and pulled back through the motor mount to keep it clear of the epoxy.
Epoxy was spread in a 3/4" wide band on the inside of the body tube where the top of the fin slots ended. That should give enough smear to affix the front centering ring well while building up a nice fillet on the top of it. The fin can was inserted just enough for the front centering ring to clear the bottom 2" of the tube. Then a 1/2" wide band of epoxy was spread along the bottom inside to give a good attachment point and fillet to the bottom centering ring. A thin bead of epoxy was spread along the thrust plate edge that will meet the body tube, and the whole thing was slid back in. I use zip ties to hold the tube together tightly for a good seal. I prefer that over rubber bands or string since the epoxy doesn't want to stick well to the zips. Makes for easy removal if I got sloppy with the epoxy.
After the fin can cured overnight, I re-inserted the numbered tabs that I cut out earlier. Those were simply glued back in place with a small drop of phenolic wood glue. No pics.
The front centering ring had a good fillet build up, so I didn't have to go back and add more.
Next up was the external fin fillets. This is where I need the most practice to get good results. The whole area was lightly sanded with 80 grit paper to allow good epoxy hold. I used a 3/4" PVC pipe and a pencil to scribe the lines where the epoxy should go and masked it all off with painter's tape. I made a mistake here. I didn't think of the fact that the width of the pencil won't let me get down far enough to scribe a line right where the PVC touches the tube. That means I masked off too high. And when I drag the PVC across the epoxy to build a smooth fillet, there's overspill at the edges that builds a small ridgeline. I had to go back with isopropanol wetted glove fingers to smooth that out. Took a lot of fiddling, but it worked out ok. Next time, I'll use my sandpaper-wrapped PVC to scratch a line to show me where to mask. Learning is fun!
This pic shows the extra epoxy bead line at the margins of where I had masked. Had to go back over it with a finger to smooth it out.
For the fillets, I used Rocket Poxy. After mixing, it was spread out thin to let air bubbles pop and let sit for 15 minutes to thicken a little. That gave me the perfect consistency for spreading the fillets. It was like toothpaste; fluid enough to self-level a little and get rid of edges, but not so thin that it dripped or ran.
Masking tape was removed about 5 minutes after each fillet pair was done. The set was left to harden a couple hours before rotating the rocket and working on the next fillets.
Hard to tell in these pics, but they came out nice and smooth with good, gradual transitions from body to fin. Fillets also wrapped around the front and back of each fin, so the whole thing just melts into the body nice and smooth.
The end result. Not completely perfect, but it should smooth out really nice after CWF and sanding rounds.
Next up is sanding and CWF to get smooth fillets. Hopefully, I'll have time this week to get to that.