Nose Cone Repair
Despite countless hours of printing I actually only finished two fully working nose cones (the work holding and turning on the lathe plus the epoxy sealing takes a lot longer than you would think on these parts) and then the one I liked the most broke right when I assembled the gun the first time. The thin wall under the bottom of the pumping barrel bore cracked:
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For the second and third assembly, I used the only other nose cone which I have done all the secondary machining and resin impregnation on and that nose cone works fine. But I would like to have a backup with me on the trip, so figured I would have a go at repairing the broken one. I felt repairing it would possibly take less time than making a new one from scratch - plus the new one might just crack in the same place again.
So, the repair had to be stronger than the original plastic and since I had the epoxy out already, I wanted to do the repair in carbon fiber.
First, I cut off the affected area - the crack shows up better here:
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I ended up turning it down a lot more and took the cut all the way up to the o-ring groove at the front (turning down the most rear of the two grooves).
Time to lay up the CF, but it was messy so no pics. I didn't bother to vac bag the part, I just used electrician's tape for compression. A trick I used was to carefully wet out a piece of CF on some mylar film I have which releases fairly easy and then when the resin has set a little, cut a suitable strip and add it to the part. This way, the wet out is much easier to control and the CF (now slightly tacky) stays in place much better for when you start rolling the stretched tape on. It's kind of a poor man's prepreg and I actually put the rest of the wet CF in the freezer, should be good for a day or two;-). After taping up the part, I chucked it in my heated 3D printer enclosure and "baked" it at 45C for half a day. (I didn't want to go too high on account of the plastic but the elevated temps should help the resin flow out and bond properly).
Here's a pic after curing when I was taking the tape off (I think the tape did a pretty nice job):
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Then I put the nose cone back on the lathe to turn the CF down to the proper diameter:
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A few more passes cleaned it up nicely. It actually machined a whole lot better than I expected but the dust is horrible and I was happy I had a respirator on:
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I had a Delrin plug in the pumping barrel bore when I laid the fiber down, too but this one has o-rings on it as I was about to do a leak test.
I was busy padding myself on the back over how well this came out with very few pin holes and what seems a reasonably good ratio of fiber (not too wet) when I remembered my "promise" to run double o-rings as often as I can so back on the lathe to cut a new rear groove:
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And finally it was time for a dunk test in the kitchen sink:
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No bubbles at 30 bar and the repaired wall of the bore seems plenty strong so I think I managed to fix this one;-)