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Classicarbon
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 I get that crak when my part stuck in mould. Can you help how to repair it? Should I make patch underneath to reinforced also? Thanks
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Hanaldo
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Easiest way is just to do a lap repair to reinforce it from behind. Depending on what sort of loads that part will see, it may also continue to propagate unless you remove the damage, which means grinding out the damaged fibres, scarfing in the edges, and building the plies back up appropriately.  For a cosmetic part, a lap repair will probably be fine.
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Classicarbon
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Group: Forum Members
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+xEasiest way is just to do a lap repair to reinforce it from behind. Depending on what sort of loads that part will see, it may also continue to propagate unless you remove the damage, which means grinding out the damaged fibres, scarfing in the edges, and building the plies back up appropriately. For a cosmetic part, a lap repair will probably be fine. It's cracked underneath too. But it's all about outside mainly.There won't be any load on it. I never made repair like that. So I clean prepare the edges and only use resin on top with patch underneath?
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torsten Ker
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first I would drill a 3 to 4mm hole on the end of the cracks, we did that with acrylic sheets, that helps to stop the crack from extending
I guess it is all about surface, you could patch the surface to repair the appearance, then do a lap repair on the inside to re-inforce it
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Classicarbon
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+xfirst I would drill a 3 to 4mm hole on the end of the cracks, we did that with acrylic sheets, that helps to stop the crack from extending I guess it is all about surface, you could patch the surface to repair the appearance, then do a lap repair on the inside to re-inforce it Is the patch need to go on top? Or make hole on the end and then use resin only or with fabric? Sorry its my first repair
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torsten Ker
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no problem
depends if you want the repair / crack to show and how thick the carbon fibre is
idealy I would cover the crack over with the same carbon fibe on the visible side, tonce hardened, sand the inside and patch that up to reinforce it
basically a double lap as in the picture above
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Classicarbon
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+xno problem depends if you want the repair / crack to show and how thick the carbon fibre is idealy I would cover the crack over with the same carbon fibe on the visible side, tonce hardened, sand the inside and patch that up to reinforce it basically a double lap as in the picture above Its 3 layers of 200g.Hope it will enough for that?
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torsten Ker
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thats a 0.5mm thickness, you may be able to carefully send a bit down on the outside so that the outside patch does not stick out too much, patch it.
Don't forget tho drill the end of the crack, once done on the outside re-enforce the inside.
How do you done finish the part, spray paint or XCR coating resin. The latter will get the best result to hide it best as possible
May be faster and cheaper to do a new part
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Classicarbon
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+xthats a 0.5mm thickness, you may be able to carefully send a bit down on the outside so that the outside patch does not stick out too much, patch it. Don't forget tho drill the end of the crack, once done on the outside re-enforce the inside. How do you done finish the part, spray paint or XCR coating resin. The latter will get the best result to hide it best as possible May be faster and cheaper to do a new part Not afford at the moment 👎😔.need to do the repair.
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Chris Rogers
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If you're trying to leave the clear finished part surface without doing an ugly repair, just hand laminate 2 plies of the same 200g material over the back with the fibers going +/-45 degrees to the crack. Extend the patch 50mm past the extents of the crack. You can do this with a brush and roller and if there's no load on the part (and the forces that initiated the crack are never likely to happen again) drilling a hole will only add a cosmetic issue to fix. Half a mm of laminate is tough to scarf. If you are going to paint the part, do the plies on the back and then once that's cured, lightly grind out the crack (making a scarf joint 30-50 mm beyond the crack like in Hanaldo's picture) and patch with two more plies from the front and then sand/grind it fair once its cured. You'll want to use normal laminating epoxy (not infusion stuff) for this because it is thicker and will stay in the fabric. Peel ply helps too if you have it. You may want to post cure the patch if the part is going to be dark colored and used outdoors. More on post-curing elsewhere on this forum.
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