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Carbon fork cutting error

Old 01-24-21, 08:46 AM
  #1  
bugello
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Carbon fork cutting error

Hi everybody

I am new on the forum with an uncomfortable situation: I currently am at my first bike-build, a genesis fugio, which all went great, until I cut the carbon fork. I did to little reaserch, and mounted the thingy to keep the saw in line the wrong way round. So I had tension on the fork whilst cutting, which at the end led to a splitting in the outter layer of the carbon fibre. I would attache an image, but this is just my first post, so I cannot yet. I just know, that carbon damage is a serious thing, so maybe someone with more experience might judge, how bad it is?

Thanks for your response in advance

Cheers
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Old 01-24-21, 09:18 AM
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I know you can't send post a pic yet but it probably would be needed to diagnose. I would be leery of delaminated carbon anything on a fork.
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Old 01-24-21, 09:37 AM
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I am not visioning what you did. My only thought is you used a dull hacksaw blade.
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Old 01-24-21, 09:57 AM
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So you tightened a worm drive hose clamp on the fork as a cutting guide? Tightened it on the steerer tube fork crown/blades side, not the side you would throw away when you finished the cut? You need pics. Keep replying until you get enough posts.
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Old 01-24-21, 09:59 AM
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So you had the cutting guide clamped on the piece you were cutting off and when you got to the end of the cut it fell and splintered the last bit of steerer tube? Impossible to give you any advice w/o seeing the damage but you likely ruined the fork.
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Old 01-24-21, 10:09 AM
  #6  
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How much of the steerer's wall thickness is splintered. Would the splinter be described as a layer or a strip?

I have seen a similar situation where a thin layer on the outside surface of the steerer got peeled off for about 1/4". The manager epoxied the missing "valley" and the end's face with a wiped on layer then installed a solid plug with more epoxy. I know the fork was working well a few yeas later as it was the service manager's personal bike and he showed that off when he was later servicing it. Andy
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Old 01-24-21, 10:37 AM
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Originally Posted by bugello View Post
which all went great, until I cut the carbon fork.
Fork failure is terrible. There is no planning, or predicting it.
If a stranger on the internet tells you its OK even from a photo, only you know if youll ever be comfortable riding it.

If you have a bike savvy resource you trust, have them look, touch, tap, and wrench on it.
The its OK would be more likely to set your mind to rest.

Barry
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Old 01-24-21, 11:10 AM
  #8  
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A picture is a must to advise on the extent of the damage. If you've cut the steerer long enough for 10-20mm of spacer (or more), you may just be able to cut off the damage. I do some unusual things with carbon steering tubes, like glue in a thread insert, rather than use an expanding plug. I've also extended the length of a steering tube by 10-15mm, using JB Weld epoxy, at the same time that I installed the permanent thread insert. As a mechanical engineer and machinist, I know what I'm doing. I want more than half of the stem clamp length to be the original steering tube.

I just finished eliminating the expanding plug on both of my newest frames. I take a 1" or 1-1/8" start nut and grind the OD so it just slips into the steering tube to use as my thread insert. I plug the steering to the appropriate depth with foam rubber and fill the entire upper 30-40mm of the tube with epoxy. Once it's cured, it's rock solid. With my current frame, I set the star nut deep enough so a future owner could saw off up to 15mm of the steerer to lower the stem, if needed. Any more wouldn't leave enough length for the 15mm headset top cover and the 40mm stem clamp height. To actually extend a steering tube, a copper tube coupling with a 1-1/8" ID is slipped over the steerer and serves as a precise mold for the extension. After the epoxy cures, the mold is removed.

Last edited by DaveSSS; 01-24-21 at 12:32 PM.
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Old 01-24-21, 10:20 PM
  #9  
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Here is the OP's photo gallery with said photo

https://bikeforums.net/g/album/20392113
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Old 01-24-21, 11:31 PM
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That bothers me... It looks like there's at least two layers of carbon ribbon lay down and a thin strip of the upper one has torn off for about 35-40mm. Way deeper into a stem clamp then I want to do. Plus the loss of what I think is a complete lay out layer makes this fork steerer one I would not try to self repair. Andy
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Old 01-25-21, 04:17 AM
  #11  
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After seeing the pic, I wouldn't ride that fork. Not even repaired.

You can risk some things on a bike, but a steerer failure is not one of them.

Whataver the cost of the fork is, it's cheaper than your life.
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Old 01-25-21, 06:59 AM
  #12  
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Don't know where you are from but unless I had an experienced shop look it over and assure me it can be repaired ( seriously doubt possible) we would not use it.
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Old 01-25-21, 07:12 AM
  #13  
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Surprised at all the people saying no, really doesn't look like much damage from the entirety of the steerer tube. I would epoxy the piece down, lightly sand it smooth and never give it another thought. If it takes that tiny amount of damage to a steerer tube to make it completely unsafe and unusable then how do any of you ever feel comfortable riding on a carbon fork? That doesn't even effect the overall structure of the layers its a part of as those are still bonded the other 98% of the way around and doesn't even go the full length of the tube.
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Old 01-25-21, 07:24 AM
  #14  
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You couldn't pay me to ride that. Order another and chalk it up, move on. Sounds like an easy mistake to make so don't beat yourself up.
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Old 01-25-21, 07:44 AM
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Originally Posted by Russ Roth View Post
Surprised at all the people saying no, really doesn't look like much damage from the entirety of the steerer tube. I would epoxy the piece down, lightly sand it smooth and never give it another thought. If it takes that tiny amount of damage to a steerer tube to make it completely unsafe and unusable then how do any of you ever feel comfortable riding on a carbon fork? That doesn't even effect the overall structure of the layers its a part of as those are still bonded the other 98% of the way around and doesn't even go the full length of the tube.
Carbon is strong as long as you apply pressure in the way it was designed to. Otherwise, it's brittle. The steerer on that pic is probably going to delaminate when subjected to normal use, and when you find out it's possible you have already smashed your skull on the asphalt on a descent.

I feel comfortable riding on a carbon fork because:

1. Mine is not damaged.
2. I remove the fork once a year to inspect the fork itself and, specially the steerer tube.
3. Nobody except me works in my bikes and I always use a torque wrench when carbon is involved.

Having said that, I don't like carbon because of this type of issues. In my, probably unpopular opinion, it doesn't have enough advantages over a good alu frame to be worth it.
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Old 01-25-21, 07:54 AM
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My next step would be to contact Genesis support. (Cap in hand).
They are unlikely to give you an OK, but might cut you some slack on a replacement.

Barry
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Old 01-25-21, 08:23 AM
  #17  
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I've never seen such extensive damage from a botched cut. A professional repair would probably cost more than it's worth. If it was cut for a large frame, it might be useable on a smaller frame. No way would I apply some epoxy just to the exterior and use it. It would need internal reinforcement too. As I've noted, it is possible to fill the entire damaged length with solid epoxy.

Next time, mark the cut line and wrap with masking tape below the line. Make short cuts around the perimeter, no more than half way through the first time around, then go around a second time to go through. A crooked cut can be fixed with a sanding block.
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Old 01-25-21, 08:27 AM
  #18  
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"It's only a flesh wound..."

Seriously, I like Barry's suggestion ^. You can categorize the risk in riding this fork in the following way. Failure Mode: steerer tube breaks, leading to immediate loss of steering control. Severity of outcome: Catastrophic (highest among: catastrophic, critical, moderate, negligible). Likelihood of outcome: Medium (mid-range among: very high, high, medium, low, very low). A catastrophic/medium is a no-go without successful mediation, it cannot be simply accepted. Mediation in this case can be repair or replacement.

You see, the likelihood is the thing that we are struggling with. Is it medium? Is it high? An experienced carbon repair shop/facility can give you a better idea. I'm saying that it is likely to fail. But what do I know. If it were my fork, I'd replace it rather than repair it.
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Old 01-25-21, 09:46 AM
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Most CF repair places do not even do forks but you could contact one of the best Carbon Repair – Calfee Design to see what they have to say about it. At least two places I've checked mention they don't do forks due to the cost is usually more than a new fork but not necessarily safety concerns. My thought is that if this shredded so easily how much strength was that layer supplying in the first place and would a repair really not be strong enough? Not going to recommend what the OP should do but is a repair really out of the question with snapped-in-two frames being safely repaired?
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Old 01-25-21, 10:01 AM
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From your picture it looks like you cut into an area that was void of Epoxy to begin with. The folks (Genesis?) who made the fork might look at it and say it was a bad fork to start with. Might be worth your while as a first step. Agree with Barry2 above
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Old 01-25-21, 12:51 PM
  #21  
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Looking at the picture more closely, it may be a case of defective lamination. The outer layer that came loose doesn't look to be bonded to the inner layer. The manufacturer might replace it, if that's the case.
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Old 01-25-21, 01:36 PM
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If its self repair and or rideable at least in part depends how and where you ride your bikes. If you are younger (stronger / heavy build) and serious (tons of miles in fast clip speeds) bike rider and ride in some hilly region that has hairy/fast downhill rides, than you may not want to use that fork.

On the other hand, if you are past any competitive bracket or don't have any such ambitions and ride for pleasure in a sporting fashion in places where you don't reach freaky speeds, the fork might well still be rideable. Maybe if you are not shaving grams, you can fill the tube with epoxy (as per advice above) or 'epoxy in' inserted smaller diameter tube of some sort (if you are handy with such jobs).

I am sure such advice might be irresponsible or what you might choose to call it but way too often, I see here on the forum discussions that totally lack the context of the particular bike riders (mostly the OPosters don't supply any context, assuming everybody here has 'the same one' as them). Here in BF, you get seasoned semi-pro mixed with mere pleasure bike riders, commuters, you name it, from all kinds of regions. Like if I lived in Alps, or some freaky downhill region in US, etc., I might have different opinion on things. Having said all that, I'd also recommend showing the fork to some shop, more qualified folks...

I used to drive a Dodge van when I was much younger and it was completely fine in my home region in Canada but when taken on a coast to coast trips across US, I found at times my brakes were not up to the job on some downhills while I was eyeing those 'run away' sandy strips and wondering if I was ripe for them... and there were other instances when it was clear, the vehicle wasn't up to it, like too high temperatures in Death Valley, or too steep, too long uphills, even elevation above sea level while in Mexico on Popocatepetl

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Old 01-25-21, 01:40 PM
  #23  
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Originally Posted by katsup View Post
Here is the OP's photo gallery with said photo

https://bikeforums.net/g/album/20392113
Ouch.
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Old 01-26-21, 07:52 AM
  #24  
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Originally Posted by Koyote View Post
Ouch.

right...

I would not ride that fork....
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Old 01-26-21, 12:13 PM
  #25  
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Originally Posted by Russ Roth View Post
Surprised at all the people saying no, really doesn't look like much damage from the entirety of the steerer tube. I would epoxy the piece down, lightly sand it smooth and never give it another thought. If it takes that tiny amount of damage to a steerer tube to make it completely unsafe and unusable then how do any of you ever feel comfortable riding on a carbon fork? That doesn't even effect the overall structure of the layers its a part of as those are still bonded the other 98% of the way around and doesn't even go the full length of the tube.

+1 Not surprised at the responses, but generally agree with this.
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