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Lengthening A Steerer Tube

Old 09-16-19, 06:33 PM
  #26  
Kapusta
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You could have just brought it to a bike shop that has a tube stretcher.
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Old 09-17-19, 07:47 AM
  #27  
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Originally Posted by Kapusta View Post
You could have just brought it to a bike shop that has a tube stretcher.
I think you need a sky hook with that.

New fork!
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Old 09-17-19, 08:17 AM
  #28  
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Perhaps bringing it to a company that does carbon repairs, would have been a reasonable solution. I'm not sure that diy is the best way to deal with carbon...
but if you're the guy who modded the trek Y-foil, go right ahead. Some hard knocks are not worth it.
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Old 09-17-19, 08:30 AM
  #29  
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Good idea, as unlike carbon fiber, wood does not asplode. But... termites.
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Old 09-17-19, 11:35 AM
  #30  
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What an incredibly foolish thing to do.


On the bright side: when the whole jerry-rigged fork comes apart and causes a crash, perhaps you will be concussed badly enough to not remember that it's your own fault.
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Old 09-17-19, 01:30 PM
  #31  
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Further thought on this one, the joint is likely a potential crack starter in a fatigue environment (pulling on handlebars while climbing for example). Seems risky to ride for any length of time/mileage.
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Old 09-17-19, 05:20 PM
  #32  
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To safely join to ends like that you need to chamfer the inside of one part and the outside of the other part to form a scarf joint. That's what is done in wood to joining two pieces together to make the board longer. IIRC it's 1 to 8 or 1 to 12. So, for example, if the wall thickness of a tube is 1mm then the chamfer would be either 8mm or 12mm depending on which ratio you used. The higher the ratio the stronger the resulting joint. A butt joint is the WEAKEST type of joint.

Cheers
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Old 09-17-19, 05:41 PM
  #33  
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It was common for racers many years ago to jam dowel down their steerers when they were racing bikes they didn't trust (and some brands were well known for such failures).
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Old 09-17-19, 05:48 PM
  #34  
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An interesting calculation to make would be the strength in bending and shear of the CF steerer and the dowel of slightly smaller diameter. I'd also do the same with a traditional steel steerer as a reality check. If the work is up to the levels of either the steel or CF, I'd have no worries - if I knew I did a good job. I would not include the epoxy in the calcs but I would use plenty and with real care to get everything bonded and the crak between the steerers filled.

Ben
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Old 09-17-19, 06:24 PM
  #35  
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Keep in mind, 20 years ago, nearly all bikes had a simple friction lap joint in the steering.



Granted, most of the steer tubes were steel, and they weren't without issues, such as the internal expanders on the left causing cracking of some stems.

Nonetheless, the style was even raced, and many riders actually survived.
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Old 09-17-19, 06:33 PM
  #36  
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Originally Posted by Miele Man View Post
To safely join to ends like that you need to chamfer the inside of one part and the outside of the other part to form a scarf joint. That's what is done in wood to joining two pieces together to make the board longer. IIRC it's 1 to 8 or 1 to 12. So, for example, if the wall thickness of a tube is 1mm then the chamfer would be either 8mm or 12mm depending on which ratio you used. The higher the ratio the stronger the resulting joint. A butt joint is the WEAKEST type of joint.

Cheers
One thinks of modern carbon fiber bike frames being monocoque, but in reality, they are made of many lap/chamfer joints that are epoxied together at the factory. And, they are strong enough to hold the bike together.

In this case, a chamfered joint would be strong, if precisely machined, and backed by an internal sleeve.
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Old 09-17-19, 06:40 PM
  #37  
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So If you want to reinforce a carbon tube why not epoxy in a steel section. Far safer and less likely to fail. JMHO, MH
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Old 09-17-19, 07:35 PM
  #38  
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Use aluminum instead of dowel and pin both tubes in addition to the epoxy.

Decent idea, wrong material used.
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Old 09-17-19, 07:56 PM
  #39  
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Originally Posted by rosefarts View Post
Use aluminum instead of dowel and pin both tubes in addition to the epoxy.

Decent idea, wrong material used.
Galvanic Corrosion will either bond everything together... or cause it to shatter.
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Old 09-17-19, 08:25 PM
  #40  
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Originally Posted by CliffordK View Post
Galvanic Corrosion will either bond everything together... or cause it to shatter.
I've spent a lot of time bolting climbing routes in a seaside locale. I probably have personally experienced galvanic corrosion more than most here.

I stand by my earlier statement. Epoxied aluminum inside a head tube simply will never see enough moisture and electrolytes to worry about.
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Old 09-17-19, 08:38 PM
  #41  
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Originally Posted by rosefarts View Post
I've spent a lot of time bolting climbing routes in a seaside locale. I probably have personally experienced galvanic corrosion more than most here.

I stand by my earlier statement. Epoxied aluminum inside a head tube simply will never see enough moisture and electrolytes to worry about.
The issue is specifically carbon fiber + aluminum.

I'm not quite sure what other conditions are necessary, as the two are frequently bonded together, sometimes with problems, often not.

If there is a well formed oxide layer on the aluminum, plus a thick epoxy layer, tit may be adequate to protect the aluminum.

Nonetheless, the issue could be avoided entirely by choosing compatible materials such as carbon fiber.

Wood also would not be susceptible to the corrosion, but could have other issues, especially with moisture if not well sealed.
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Old 09-17-19, 08:56 PM
  #42  
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Just to add to this, the dowel and the bonded carbon fibre being "strong" isn't necessarily a good thing.
It needs to take in consideration the way a force is dissipated on a given "original" piece/section.


By adding a dowel and/or a piece of bonded carbon fibre to a section, if the strength of said section is different from the original, you're also changing the way forces/stresses are dissipated, creating weak spots.

As said above by a few people already, this does not sound very safe, especially given that a failure of such component is pretty catastrophic.
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Old 09-18-19, 09:01 AM
  #43  
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Originally Posted by CliffordK View Post
Keep in mind, 20 years ago, nearly all bikes had a simple friction lap joint in the steering.


That's a nice diagram, but it seems odd to me that it depicts the wedging action happening at the butted section. In practice, wouldn't it be in the non-butted section, where more linear contact is available?
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Old 09-18-19, 09:33 AM
  #44  
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Originally Posted by RubeRad View Post
That's a nice diagram, but it seems odd to me that it depicts the wedging action happening at the butted section. In practice, wouldn't it be in the non-butted section, where more linear contact is available?
I remember the diagram, and I think it's from Sheldon's website discussing proper mounting of quill stems. You're right. This is a diagram of a too long stem or high butted section preventing the wedge/expander from binding adequately.

While I enjoy reading how we could solve this issue, no one has considered the cost/benefit. A new fork costs $170 on up. What does it cost to machine an identical conical chamfer into the tube and donor steerer and epoxy with a carbon overlay? If it were wood, you might key the chamfer because the only resistance to rotational shear would otherwise be the glue bond, I'm not sure if that's helpful in a layered material like carbon fiber. Unless you're looking at $250+ for a new fork, I'd think replacing is the most cost effective option.
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Old 09-18-19, 09:53 AM
  #45  
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FWIW, this works for steel steerers. They are brazed, not epoxied, and the inner sleeve is also steel.

Probably not as strong as the original and definitely a bit heavier but when talking about something that is orders of magnitude stronger than necessary, it works.

For this carbon fork, it all depends on how I was planning to use it. Commuting on relatively slow roads, usually alone, preferably out of traffic - do what I said earlier with an aluminum sleeve and pins.

50+ mph descents, pack rides, proximity to traffic, rough surfaces - new fork.
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Old 06-20-20, 12:27 PM
  #46  
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The wood dowel snapped and I crashed descending at a high speed. Fortunately this catastrophy resulted in only road rash and soreness for me, but it could have been much worse. Obviously the stress endured by the steerer tube is much greater than I anticipated.
See my original post " Lengthening a steerer tube".


Last edited by hrdknox1; 06-21-20 at 09:22 AM.
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Old 06-20-20, 02:03 PM
  #47  
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Wow -- I'm glad you learned that lesson instead of me!

What kind of wood was the dowel? I imagine your average home despot dowel, which is light as air, is not that strong.
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Old 06-20-20, 02:30 PM
  #48  
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Wow. just wow.

Glad you walked away.

Brave of you to come back and post the results. There was obviously some difference in opinion so maybe your hard learned lesson will help others.
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Old 06-20-20, 02:53 PM
  #49  
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Originally Posted by hrdknox1 View Post
.... I purchased a cheap fork ($48) off eBay .....
I would have just used that Ebay fork!
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Old 06-20-20, 03:07 PM
  #50  
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Originally Posted by RubeRad View Post
Wow -- I'm glad you learned that lesson instead of me!

What kind of wood was the dowel? I imagine your average home despot dowel, which is light as air, is not that strong.
Yep, The Home Depot.
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