Kframe
Well-Known Member
This past weekend I attempted L1 certification and I would have achieved it but the 3D printed nosecone cracked in two upon landing on dirt.
It was a weird break, there was no paint loss at all on either section, and it cleaved right along the grain of the filament, so it must have just been a weak spot. But really frustrating because that meant failing the cert attempt.
The printed nosecone also had an integral crossbar for attaching the shock cord, and a couple rocketeers commented that they were surprised it didn’t fail at that point and that for high power they really don’t prefer 3D printed cones.
So I set to repairing AND strengthening the cone so I can attempt L1 again next month.
I first cut off the crossbar, which also gave me better access to the interior for repairs.
Next, and I don’t have pics because my hands got messy, I mixed up some JB Quick and coated the inside or the broken off tip - and then laid in a ‘collar’ of fiberglass cloth that extended above the break about an inch all around.
As that set up I quickly whipped up more JB Quick and dropped a glob down into the cone onto the flat of the epoxy’d BBs , and smeared another big glob onto the nuts of a U-bolt, which I then stuck in, completely covering the nuts with a quarter inch of JB.
I gave that a minute to start setting and then with CA gel I glued the two cone pieces back together.
Then I spread more JB down inside the larger piece, pressed the collar of fiberglass around the walls of it and then spread a copious amount of JB completely over the fiberglass and then around the walls of the cone all the way to the mouth.
This is what it was like:
The BB’s were preexisting from the original building.
Here you can see the JB on the walls and the U-bolt at the bottom (top?)
After the JB fully set I sanded with 120, 220 and 400 until the fault line could not be felt.
After some primer, wet sanding to 800 and then color the damage is invisible!
In a few days I’ll shoot it with some clear and it will be good to go for round two!
It was a weird break, there was no paint loss at all on either section, and it cleaved right along the grain of the filament, so it must have just been a weak spot. But really frustrating because that meant failing the cert attempt.
The printed nosecone also had an integral crossbar for attaching the shock cord, and a couple rocketeers commented that they were surprised it didn’t fail at that point and that for high power they really don’t prefer 3D printed cones.
So I set to repairing AND strengthening the cone so I can attempt L1 again next month.
I first cut off the crossbar, which also gave me better access to the interior for repairs.
Next, and I don’t have pics because my hands got messy, I mixed up some JB Quick and coated the inside or the broken off tip - and then laid in a ‘collar’ of fiberglass cloth that extended above the break about an inch all around.
As that set up I quickly whipped up more JB Quick and dropped a glob down into the cone onto the flat of the epoxy’d BBs , and smeared another big glob onto the nuts of a U-bolt, which I then stuck in, completely covering the nuts with a quarter inch of JB.
I gave that a minute to start setting and then with CA gel I glued the two cone pieces back together.
Then I spread more JB down inside the larger piece, pressed the collar of fiberglass around the walls of it and then spread a copious amount of JB completely over the fiberglass and then around the walls of the cone all the way to the mouth.
This is what it was like:
The BB’s were preexisting from the original building.
Here you can see the JB on the walls and the U-bolt at the bottom (top?)
After the JB fully set I sanded with 120, 220 and 400 until the fault line could not be felt.
After some primer, wet sanding to 800 and then color the damage is invisible!
In a few days I’ll shoot it with some clear and it will be good to go for round two!
