I would like to launch this rocket again but really was nervous about fin breakage after its maiden. I upgraded the chute to one of Gary's very nice 21" jobbies, but upon finding out that Gary's original was
breaking a fin on every flight (or nearly), I decided that reinforcement was needed if she were to fly in the future. After discussing it with Gary, I decided to just do what I do best: take a simple problem and come up with a complex solution, albeit one that would (I hope) be effective and fun to implement. And so all roads pointed to 3D printing.
I found a new inexpensive hub on 3DHubs nearby and had these cuffs printed for the fin leading edges:
I debated materials for a while. I was gonna go with PETG, but it's a bit more expensive and I haven't used it before. My concern was that it would be too flexible. Maybe not, but I didn't want to risk it. I also didn't want to take a chance with ABS warping or having poor layer adhesion. So I went back to good old PLA, 100 micron. I printed them in red in the hopes that I wouldn't need to paint them.
I really didn't know how thick to make them. In the end, I probably made them a bit thicker than they needed to be. They are VERY stiff. Total weight for four is around .6 oz. I had an extra printed in case I messed them up. Oh also, this was actually my second batch; the first batch was too small due to a couple of measurement errors on my part. The new batch was the correct size.
Anyway.
Out of the printer, they didn't have the smooth round profile I was looking for, so I performed what could only be called an obscene amount of sanding (PLA is *hard*) to, shall we say, "round them into shape". Here's the before and after (well actually the after and before):
After shaping with a 180 grit sanding sponge, I went up the ladder all the way to 1500 grit, after which they were pretty smooth. Not perfect, but still quite good:
I checked fit before continuing. The channels needed a bit of opening up to achieve a nice snug fit on the fins. Perfect. Then I applied 3 very quick coats of Future using a paper towel to wipe it on. To hold the parts while applying and drying, I threaded them onto a piece of 1/8" square dowel and held them in a clamp:
After the Future, they looked pretty darn good, definitely no need for paint and a pretty good match for the existing fin color. That made me happy.
The fins were prepped simply by sanding the paint off the leading edges, so the epoxy would have at least one raw surface to bond to:
I tried not to think to hard about what I was doing here. I was so proud of this paint job and here I was making hash out of it. But all in service of the greater good, so I pressed on.
For each part, a nice bead of 30 minute epoxy was carefully laid into the channel...
...and then it was stuck onto a fin. I had practiced applying them enough times during fit testing that I knew pretty well exactly how to do it to get them to land in the correct position the first time (or at least close enough so I wouldn't need too much adjustment). And here is a fin with the cuff applied:
Pretty good, eh? Here's an end view of one of them showing how it fits on. Sorry for the blurriness but you get the idea:
The very top of one of the cuffs just wouldn't lay flush to the "muscle". I tried for a while but really there was nothing I could do about it, so I just forgot about it. You only see it if you inspect closely, and I'm certainly not concerned about aerodynamics (that train left the station a loooong time ago for this rocket):
And here is the finished fin can.
I'll say this: if these don't prevent breakage then I shall give up and retire this rocket. As it stands now, I will be ordering up some Aerotech E15s for launch this spring or summer.