Carbon forks. Lateral movement
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  1. #1
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    Carbon forks. Lateral movement

    Have a new full carbon fork and had it off the bike to cut the steerer. I was inspecting because I already got some scratches, I think from the spokes but I was going over it.

    Don't know why but I was putting a bit of lateral pressure on the blades. They do go in and out a few mm. Even my dropouts arnt totally flush with the hub. They move a few mm when tightened but I guess that's normal. I don't think I put too much pressure when handling them but hurt some weird noises. I don't think should be hearing anything. Could I have damaged them? I can't replicate those noises anymore by putting pressure. It was just the first few times. The noises had to come from the fork. It was off the bike

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    Quote Originally Posted by sheepherder View Post
    ...I was putting "a bit" of lateral pressure on the blades... ...I don't think I put "too much pressure" when handling them but hurt some weird noises...
    Vague: [veyg]; not definitely established, determined, confirmed, or known; uncertain ;-)

    Well, yes. The sound you heard could've been the fork cracking... or not.

    The likelihood is very (!) low that you did any damage. Guys who love steel, aluminum and titanium often refer to carbon as "plastic" and perpetuate myths of weakness, etc. Nope. Assuming the fork was made by one of the quality manufacturers, it's ridiculously strong. Watch some youtube vids on the topic - guys trying to break frames and forks with massive presses, dropping bowling balls on them etc. Granted, they're mostly focused on forces encountered while riding - so, more fore/aft than lateral - but it'll give you a good idea of what the material can take.

    But I guess it could come down to your definition of "bit" and "too much" ;-)
    Last edited by OldZaskar; 1 Week Ago at 04:18 AM.

  3. #3
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    How on earth would it be the spokes unless you had broken one/some? And of course this should be posted in 'bikes/frames/FORKS'. You've been here for years and should know that.
    Last edited by cxwrench; 1 Week Ago at 06:58 AM.
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    I scratched the fork with the spokes when putting the wheel on.

    I don't think the spokes damages the fork. But when I started putting pressure laterally that I did damage becauaw of some weird noises

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    Quote Originally Posted by sheepherder View Post
    I scratched the fork with the spokes when putting the wheel on.

    I don't think the spokes damages the fork. But when I started putting pressure laterally that I did damage becauaw of some weird noises
    So you scratched the paint but somehow thought you'd done structural damage and then squeezed the fork blades together to see if it was broken? Is that what happened?
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    Quote Originally Posted by cxwrench View Post
    So you scratched the paint but somehow thought you'd done structural damage and then squeezed the fork blades together to see if it was broken? Is that what happened?
    I don't know why I squeezed them together. Pure stupidity, I don't know.
    Buy yeah I flexed them in and out a bit. Not crazy pressure but the sound wasn't good

  7. #7
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    Quote Originally Posted by sheepherder View Post
    I don't know why I squeezed them together. Pure stupidity, I don't know.
    Buy yeah I flexed them in and out a bit. Not crazy pressure but the sound wasn't good
    It shouldn't have caused any damage, forks are crazy strong. But...don't do it again.
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    tlg
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    Quote Originally Posted by sheepherder View Post
    Could I have damaged them?
    Quote Originally Posted by sheepherder View Post
    Buy yeah I flexed them in and out a bit. Not crazy pressure but the sound wasn't good
    No one will ever be able to answer your question since there is no way of knowing what metric "a bit" and "crazy" is measured by.

    Quote Originally Posted by sheepherder View Post
    I scratched the fork with the spokes when putting the wheel on.
    How the heck is that even possible Spokes aren't that sharp or abrasive. You must've been slamming the wheel in there.

    My speculation is, if you're careless enough to scratch the fork with the spokes, you're careless enough to damage the fork with "a bit" of lateral force. I would recommend a new fork. If not, be sure to have good dental and health insurance.
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    if you just used one hand to squeeze the fork legs together at the dropout point, then it's pretty hard for you to squeeze hard enough to make the fork leg(s) crack. But if you clamp the dropouts together using both hands in a vise-like grip, then I can see the leg(s) cracking.

    However, it could be that the fork was already pre-damaged, and now you're just pushing it over the top. The fack that you hear crackling sound is NOT good. That sounds like carbon fiber delaminating! Well, at this point, if it were me, I'd give the fork a few more squeeze using one hand to see if I can hear any crackling sound while paying attention to any delaminating paint or clear coat.

    Last think you want to to now is to not test the fork further and continue to use it as it while pretending/praying everything is all ok. It's not.

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    Or take it to a shop and get a second opinion (from a pro)

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    Quote Originally Posted by OldZaskar View Post
    Or take it to a shop and get a second opinion (from a pro)
    Very few "bike shops" have the capability to inspect carbon fiber delamination.
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    Seriously, no solid fork should move "a few millimeters". Not even a single millimeter, nor even a quarter of a millimeter.
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    Quote Originally Posted by No Time Toulouse View Post
    Seriously, no solid fork should move "a few millimeters". Not even a single millimeter, nor even a quarter of a millimeter.
    You're kidding, right? They ALL have some flex. And more than a few millimeters.
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    Quote Originally Posted by No Time Toulouse View Post
    Seriously, no solid fork should move "a few millimeters". Not even a single millimeter, nor even a quarter of a millimeter.
    That would be impossible. Unless perhaps you wanted a 5lb fork.
    I just measured a few bikes. Just using 2 fingers and not much force.
    Road bike: 4mm
    Cross bike: 5mm
    MTB: 2.5mm

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    Quote Originally Posted by OldZaskar View Post
    Vague: [veyg]; not definitely established, determined, confirmed, or known; uncertain ;-)

    Well, yes. The sound you heard could've been the fork cracking... or not.

    The likelihood is very (!) low that you did any damage. Guys who love steel, aluminum and titanium often refer to carbon as "plastic" and perpetuate myths of weakness, etc. Nope. Assuming the fork was made by one of the quality manufacturers, it's ridiculously strong. Watch some youtube vids on the topic - guys trying to break frames and forks with massive presses, dropping bowling balls on them etc. Granted, they're mostly focused on forces encountered while riding - so, more fore/aft than lateral - but it'll give you a good idea of what the material can take.

    But I guess it could come down to your definition of "bit" and "too much" ;-)
    It's a new Cannondale fork. I've seen all those videos and they all smashing the fork in the other direction.

    Quote Originally Posted by cxwrench View Post
    It shouldn't have caused any damage, forks are crazy strong. But...don't do it again.
    Any idea what the sound could if been.

  16. #16
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    Quote Originally Posted by sheepherder View Post
    Any idea what the sound could if been.
    Absolutely... the sound of concern .

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    Quote Originally Posted by tlg View Post
    Very few "bike shops" have the capability to inspect carbon fiber delamination.
    Going on a limb here... a pro mechanic at a bike shop would have seen and held more forks than the OP. He would probably:
    1. Flex, push, pull, look, listen... and then
    2. Tell the OP the fork is fine... or
    3. Suggest the fork be sent to the manufacturer to be properly inspected... or
    4. Suggest the fork be replaced with "This one"

    All of which would be better than asking the interwebs to weigh in without the advantage of being able to see, hold, push, pull... on the OP's fork ;-)

    Sort of related. A buddy of mine was clamping his bike - fortunately by the seat tube... a carbon seat tube - into my old workstand. It was the type with a pre-set cam-style closure - sort of like vice grips. Terrible design by the way. Right as he clamped it, we heard a sickening sound - imagine a small bag of potato chips in the bottom of a bag... and then sit on the bag. He said "****. What was that sound?" I said "That sounded like about $300... get the 4mm wrench."
    Last edited by OldZaskar; 1 Week Ago at 04:27 AM.

  18. #18
    tlg
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    Quote Originally Posted by OldZaskar View Post
    Going on a limb here... a pro mechanic at a bike shop would have seen and held more forks than the OP. He would probably:
    1. Flex, push, pull, look, listen... and then
    2. Tell the OP the fork is fine... or
    3. Suggest the fork be sent to the manufacturer to be properly inspected... or
    4. Suggest the fork be replaced with "This one"
    #1 Would't detect delamination. Pushing, pulling, listening is a useless method to detect delamination.
    #2 It would be foolish of the shop to give the A-ok and foolish of the customer to trust the shop.
    #3 The manufacturer isn't going to risk liability over a non-warranty user created issue. They'll say replace it.
    #4 Yup, the only smart option. Which can be advised on the interwebs since visual inspection is useless.

    Of course there's option #5. Send it to a carbon fiber repair shop than can properly inspect it via ultrasound and thermal imaging.
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    My bad, I thought he was talking about LINEAR movement. Even so, moving dropouts even 2mm is a b!tch...
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  20. #20
    tlg
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    Quote Originally Posted by No Time Toulouse View Post
    My bad, I thought he was talking about LINEAR movement. Even so, moving dropouts even 2mm is a b!tch...
    Nope.

    Quote Originally Posted by tlg View Post
    I just measured a few bikes. Just using 2 fingers and not much force.
    Road bike: 4mm
    Cross bike: 5mm
    MTB: 2.5mm
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  21. #21
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    You just got out a tape measure, pulled the wheels off three bikes, measured your two-finger squeeze rates... to make an internet point. Dude, you win. ;-)

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    Quote Originally Posted by aclinjury View Post
    if you just used one hand to squeeze the fork legs together at the dropout point, then it's pretty hard for you to squeeze hard enough to make the fork leg(s) crack. But if you clamp the dropouts together using both hands in a vise-like grip, then I can see the leg(s) cracking.

    However, it could be that the fork was already pre-damaged, and now you're just pushing it over the top. The fack that you hear crackling sound is NOT good. That sounds like carbon fiber delaminating! Well, at this point, if it were me, I'd give the fork a few more squeeze using one hand to see if I can hear any crackling sound while paying attention to any delaminating paint or clear coat.

    Last think you want to to now is to not test the fork further and continue to use it as it while pretending/praying everything is all ok. It's not.
    I definitely didn't squeeze that tight. It was just the initially flex that made some noise. Can't even say it was a crackling noise. I was surprised to hear anything.

    I've looked the paint over with a flashlight and no damage. Absolute no more noise if I put pressure on them again and they feel real strong

  23. #23
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    Quote Originally Posted by OldZaskar View Post
    You just got out a tape measure, pulled the wheels off three bikes, measured your two-finger squeeze rates... to make an internet point. Dude, you win. ;-)
    Nope. A digital caliper. And 5min time. I was gonna do two other bikes but they were on trainers.
    Better than making up false statements about how much fork blades deflect.

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    Quote Originally Posted by sheepherder View Post
    I definitely didn't squeeze that tight. It was just the initially flex that made some noise. Can't even say it was a crackling noise. I was surprised to hear anything.

    I've looked the paint over with a flashlight and no damage. Absolute no more noise if I put pressure on them again and they feel real strong
    I got a bunch of forks here. Just tested them by squeezing them together using 2 fingers and a thumb. I tried to squeeze as hard as I could, I'm guessing the effort felt like trying to lock down on a skewer. Deflection was about 4mm.

    Carbon fiber is very resistant to fatigue, so if your fork is in fact still in good condition, you should be able to squeeze it pretty hard with 2 fingesr and a thumb over and over again and the legs would still be ok (i.e., it shouldn't give out any hint or wimper of sound).

    Another thing you could do is take a coin and tap the fork throughout. Tap both legs, inside and outside, all over. Assuming the fork is symmetrical, both legs should give out similar sound when "symmetrical areas" from both sides are tapped. So tap one side, then go to the other side and tap the same region, you should get the same sound. Of course there is always a slim chance that both same positional regions of the 2 legs are cracked, thus giving you the same sound, thus making this test give a false negative; however, the chances that there is a crack on both legs at the exact same locations is... very slim.
    Last edited by aclinjury; 1 Week Ago at 08:53 PM.

  25. #25
    tlg
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    Quote Originally Posted by aclinjury View Post
    Another thing you could do is take a coin and tap the fork throughout.
    The coin tap test is useless on a carbon fiber bike. It only works (potentially) on large consistent shaped objects. It'll never work reliably on an irregular shaped bicycle with compound shapes.

    carbonbikerepair.com.au/articles/82-the-limitations-of-tap-testing]The Limitations of Tap Testing
    The Limitations of Tap Testing
    You will often see reference to the tap test or coin test method for finding damage in composite materials. It is used in aerospace, so it must be good, right?
    As a qualified quality assurance technician having held CASA, FAA and a host of aerospace quality certifications, I am able to clarify this information.

    How does the tap test work?
    The method involves gently tapping the part with a special tap hammer or even a coin, hence the coin tap reference, you don't want to tap too hard though as this may create damage. The impact energy travels through the part causing it to resonate or ring in the same way a tuning fork rings at a certain frequency or note. If there is an inconsistent condition such as an unbond or major delamination, the audible ring will be different. By listening to the tonal changes, an indication that there may be damage can be noted. The method is dependant on the skill and experience of the operator. It is cheap and simple and works reasonably well for these type of defects. In aerospace Non Destructive Inspection it is a backup (known as a secondary) method or used in non critical applications, the primary method is ultrasound, so parts that are critical get an ultrasound scan.

    What can it find?
    Typically the method is used for finding flaws in bonded parts such as unbonds on flat panels between the composite or metal skin and the honeycomb core. Because it is an acoustic method, it is very dependant on the geometry of the part in the same way a different length tuning fork provides a different note. Thus the operator needs to be aware of how the sound wave or vibration travels through the part. Large consistent flat areas with thin skins are the most suitable, as the skin thickness increases and the curvature increases the results are less reliable. It is typically ok for finding unbonds in the composite skin to the honeycomb core greater than about 10mm in diameter. It is simple for an experienced technician to give a part a quick "tap" at any obvious visual damage indications, any suspected damage found is then scanned with the primary ultrasound method to validate.

    What can't it find?
    Tap testing is typically not recommended for laminate testing as it is unreliable in finding common laminate defects. For bonded parts if the damage is below a critical size or the material thickness is above a limit or located within geometry constraints it will not be able to find the damage. Porosity and voids, resin dry and resin rich areas also cannot be identified unless they are so bad it is obvious visually anyway. Light impact damage known as BVID, (barely visible impact damage) will also not be detectable. Background noise etc can also interfere with any results.

    How is this related to assessing damage in bikes?
    Bike frames are typically made from thin laminate with localised thicker areas at the higher stress joins. Bonded parts are limited in modern frames and typically no honeycomb core is used in the way some aircraft panels are constructed, with the exception of some disc wheels. On frames with bonded parts at the tube junctions such as imternal or external lugs, the compound curvature geometry and laminate thickness at the lug areas as well as the tube shapes contribute to getting unreliable information from a tap test. The damage also needs to be above a critical size dependant on the geometry of the inspected area, hence a 5mm defect in a seat stay that is only 10mm wide would probably not be found but will have a large effect on the structural integrity. Other factors such as internal joins, fillers and inserts will also affect the ability to get meaningful results.

    So as you can see, the tap test method on its own is not able to reliably detect damage in these type of parts.

    Conclusions
    Typically damage to bike frames that is able to be found with the tap test can mostly be identified visually as the primary method and then may be confirmed with a tap test as a secondary method. If an indication "taps" it is likely to be damage, if it does not "tap" there still may be damage however due to the limitations explaned above. Overall it is useful for confirming certain types of damage as a secondary method as long as you understand the limitations of the method.


    Rest assured we won't be giving up on our ultrasound scans any time soon, as it is a proven reliable primary method.
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