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  1. #1
    Chieftain
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    Small cut/scratch in carbon frame...

    I put small cut today with a very sharp knive (don't ask) on my cf frame, just above the bottom bracket on the seat tube. It's about 1cm long and wide enough to get your fingernail in. It goes through the clear coat and paint, possibly to the top of the fiber. Can this be easily touched up, or does it need inspected, and by whom?

  2. #2
    W.W.DZ.D? cedricbosch's Avatar
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    Turn that thing over to the NIH or else

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    Senior Member Jakedatc's Avatar
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    doomed....
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    Dog is my co-pilot 2manybikes's Avatar
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    Quote Originally Posted by Jakedatc View Post
    doomed....

    [SIGPIC][/SIGPIC]

  5. #5
    Senior Member tkehler's Avatar
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    You must cease and desist with the arcane bicycle circumcision rituals.

    (Joking aside, I have no idea about that cut's significance. Sorry.)

  6. #6
    Senior Member Chevy's Avatar
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    unless you can see cut fiber ends don't worry about it. the layup consists of multiple layers of resin and fibers so no worries unless you trashed an entire layer of fibers or the cut goes through several layers. put a couple dots of super glue on it to make you feel better Composite structures are not susceptible to fatique concentration like metal so crack propagation from the cut isn't likely

  7. #7
    Senior Member
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    so what did you do to it?
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  8. #8
    Senior Member phallenthoul's Avatar
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    Quote Originally Posted by humboldt'sroads View Post
    I put small cut today with a very sharp knive (don't ask) on my cf frame
    why did you cut your frame?
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  9. #9
    Senior Member kleng's Avatar
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    Quote Originally Posted by phallenthoul View Post
    why did you cut your frame?
    Ah!!! the old knife as a screwdriver trick.

  10. #10
    Senior Member leakysieve's Avatar
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    All around the bottom bracket is they lay-up a significant number of layers cause is where a lot of strength and stiffness is needed. You should be fine. If cracks extending from the ends of the cut begin to form, then i would start to worry.
    Sometimes, I have to wonder.

  11. #11
    Chieftain
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    Quote Originally Posted by Val23708 View Post
    so what did you do to it?
    Well, I was....
    Quote Originally Posted by phallenthoul View Post
    why did you cut your frame?
    I was..
    Quote Originally Posted by kleng View Post
    Ah!!! the old knife as a screwdriver trick.
    No...almost though-

    I was cutting zip ties after putting on my cadence meter that didn't end up working anyway...

  12. #12
    Village Idiot
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    Quote Originally Posted by humboldt'sroads View Post

    I was cutting zip ties after putting on my cadence meter that didn't end up working anyway...
    I almost did that. I cut through the clear on my CAAD9. It was at the BB weld though, and I just put clear nail polish over it. No worries, but it's not carbon and I didn't go through the material.
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  13. #13
    Senior Member
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    Quote Originally Posted by humboldt'sroads View Post
    Well, I was....

    I was..

    No...almost though-

    I was cutting zip ties after putting on my cadence meter that didn't end up working anyway...
    ah see well we can understand that
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  14. #14
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    Like most on this thread I agree that it is likely that no fibers were cut by the the knife slip. But with respect to the non-importance of damaged fiber, in the words of Bill Lumbergh: “I’m gonna have to disagree with this.”

    My comments are based on the work I do in aerospace, primarily spacecraft hardware. It is true that many types of composite hardware have great damage tolerance. In the pursuit of low weight much of that robustness can be lost. It is also true that the bottom bracket is an area of many ply's but I believe the reason is driven by the fact that the bottom bracket area is highly loaded. If the bottom bracket area is a location of flex, it is exactly the area I would be concerned about propagation.

    The protocol in my industry for any damage (or suspected damage, hardware is guilty unless proven innocent) is to not trust it unless a cognizant analyst has reviewed the possible damage with respect to the load cases and calculated margin of safety.

    I suspect that a 900 gram frame will be more likely to require a repair that a 1500 gram frame (due to reduced safety factors) but unless there is reasonable certainty that fibers were not cut/broken I strongly advice contacting the manufacturer for their advice. Unfortunately the frame's maker may be operating under prudent legal rather than engineering practices. If that is the case, they will probably say that any damage is too much damage. Someone from the bicycle industry may be able to make a general comment but without knowing the depth of the cut and the local margin of safety it is as they say, just an opinion.

    My colleagues and I have obtained damaged frames over the years from shops doing replacement work. We have performed repairs to the frames as if they were “flight hardware” and successfully ridden these frames for years. However, our philosophy was to repair or reinforce any questionable areas before use.


    Kerry P

  15. #15
    mad11:11one MANTEIGA's Avatar
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    shouldnt use super glue on carbon!

    Quote Originally Posted by Chevy View Post
    unless you can see cut fiber ends don't worry about it. the layup consists of multiple layers of resin and fibers so no worries unless you trashed an entire layer of fibers or the cut goes through several layers. put a couple dots of super glue on it to make you feel better Composite structures are not susceptible to fatique concentration like metal so crack propagation from the cut isn't likely
    cyanoacrylate cant flex like resin, very brittle under cold temp, very hard to work with, will melt through clear coat instantly.. cant wipe up!.
    "I KNOW OF NO REASON WHY THE *** POWDER TREASON SHOULD EVER BE FORGOT........."
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  16. #16
    Banned
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    Bad news: end of frame

    Good news: you now have a reason to get a new one

  17. #17
    No matches Flatballer's Avatar
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    Quote Originally Posted by humboldt'sroads View Post
    I was cutting zip ties after putting on my cadence meter that didn't end up working anyway...
    I figured. Use diagonal cutters in the future and go right up to the frame, but not into it.

  18. #18
    Senior Member
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    I think the important thing to note between the two useful replies here, (Chevy and KerryP) is whether or not you cut any fibers or it's just the resin/clearcoat. If you didn't get to any fibers, I really wouldn't worry about it. If you did, then it depends entirely on how robustly your particular frame was designed. I have a VERY hard time believing that the designer designed the margins so close, that a single ply of carbon would mean the difference between a good product and failure, though it's impossible to know for sure.
    Quote Originally Posted by caloso View Post
    Good lord. Why do we keep trying to make cycling attractive to people who are not attracted to cycling?

  19. #19
    Chieftain
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    Ok - so I checked it out under better light...I mean, the cut is 1/2 inch long at most, and looks like it went through paint, but I don't see anything that's obviously a fiber, but the cut really is too small to tell. I can tell that if any fiber got cut, it wouldn't be more than a millimeter or two and one layer thick, and that's a big if, from what I can tell. At this point, I can't afford a new frame, even an aluminum one, so I think I'm gonna ride this and see if it makes any noise and see if the clear coat cracks any.
    Further opinions?

  20. #20
    Senior Member Tariq08's Avatar
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    i think they're messing with you dude..

    at least i hope so anyway, i have mad nicks in my frame just from riding on rough roads
    Felt F4

  21. #21
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    The scar on my thumb is from cutting a cable tie with a boxcutter.


  22. #22
    Senior Member MrCrassic's Avatar
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    Just ride the bike. Worst case scenario, your frame breaks while going downhill, then you fall down a ditch and die. Best case, you'll enjoy your bike for a while
    Ride more.

    Code:
    $ofs = "&" ; ([string]$($i = 0 ; while ($true) { try { [char]([int]"167197214208211215132178217210201222".substring($i,3) - 100) ; $i =
     $i+3 > catch { break >>)).replace('&','') ; $ofs=" " # Replace right angles with right curly braces

  23. #23
    No matches Flatballer's Avatar
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    Quote Originally Posted by kpfeif View Post
    The scar on my thumb is from cutting a cable tie with a boxcutter.

    I have a scar on my thumb from cutting a zip tie with a knife... towards my other hand. Brilliant!

  24. #24
    Senior Member bigtea's Avatar
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    Actually the fix is quite simple.

    1) loosen and then detach all components from frame.
    2) slide out defective carbon fiber frame
    3) insert superior titanium frame
    4) reattach and tighten components.
    I will make you suffer on the downhills with my superior body weight.

  25. #25
    Senior Member Chevy's Avatar
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    Quote Originally Posted by humboldt'sroads View Post
    Ok - so I checked it out under better light...I mean, the cut is 1/2 inch long at most, and looks like it went through paint, but I don't see anything that's obviously a fiber, but the cut really is too small to tell. I can tell that if any fiber got cut, it wouldn't be more than a millimeter or two and one layer thick, and that's a big if, from what I can tell. At this point, I can't afford a new frame, even an aluminum one, so I think I'm gonna ride this and see if it makes any noise and see if the clear coat cracks any.
    Further opinions?
    Ride it.

    Okay a short tutorial on composites. We have been building metal airplanes for 85 yrs and composite ones for 25.There are several types of non destructive inspections you can do for metal (dye penetrant, X-ray, eddy current, etc) but very few for composite structures. Ultrasound is about the only game in town. Also our capability to model composites' behavior under various loads is still in it's infancy. Especially a complex shape.
    As a result for aircraft applications (and I suspect bike frames) composite structures are grossly overdesigned. (spacecraft are a different story then most aircraft structures because they will except lower margins to shave a few pounds) If the resin fiber matrix can carry load X, we typically design to twice that due to the uncertainities involved.
    How these things typically fail are void propagations between layers, ; i.e. delamination, followed by failures of the layers themselves . Think phone book. No one can tear a whole phone book in half but a toddler can destroy one a few layers at a time once it is "delaminated". Failure across intact fiber layup, i.e. cracking simply never happens unless the loads are horrendous.
    So if you want to have a warm fuzzy then get a quarter and do a "tap test". This is what we do with really really expensive composite aircraft structures before we untrasound them. You can actually map the edges of a void pretty well with a quarter. Once we know there is a void we will mark the edges after an ultrasound and check it periodiaclly with a tap test to make sure it isn't growing. Tap the edge of the coin along the frame and it should have a nice crisp click noise in response. If it clunks instead of clicks then that means there is a void underneath. Since the BB and tubing are hollow they will have a drum like response to a degree but a real void sounds sorta dead. Assuming you have had no voids propagated yet, tap the suspect area and listen. Do this occaisionally and as long as it keeps clicking then you are fine. Even if it starts clunking you can probably ride it a very long time before it falls apart.
    Yes composite frames fail. Poorly designed, poorly built frames of all kinds fail. But if a composite structure doesn't fail in it's infancy they usually live forever unlike aluminum or steel.
    Remember Orville and Wilbur started off building bikes...

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