Question About Carbon Handlebars- Mtbr.com
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  1. #1
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    Question About Carbon Handlebars

    So first off, I've been lurking for quite a while now. Hopefully this is a good first post to get started on here. Looking forward to being more involved with you guys moving forward! What a valuable resource this forum is.

    My question is about custom lugged carbon handlebars. Think like the ones that PVD has been using on his recent builds. With the way the next few bikes I am designing are going, something along those lines does seem like the best solution to the problem. (And I think they look just fantastic. Very nice custom touch.)

    But anyway, the root of my question is this. I've never worked with carbon. I'm a long-time welder/fabricator, and machinist. But after reading about the crash PVD had, carbon kinda scares me to be honest. And I by no means treat my bikes 'well' Pisgah, NC is my backyard, so my bikes get 'very well tested' we'll say.

    Do you guys have any good resources I can read up on to help make an informed decision on the right weave, wall thickness, other factors I'm ignorant of, etc.? The performance gains are too tempting. I just want to educate myself the best that I can on a good starting point before committing to the risk and money of doing some real world testing.

    If this has already been discussed on another thread, My bad. My searching / Google-ing is always a bit lacking. Sometimes you just gotta know the right term to search.

    Thanks in advance. I already owe you guys more beers than I'll admit just from lurking around here for a while

  2. #2
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    I’m in the process of building a frame which involves carbon tubes bonded into steel lugs. The adhesive of choice appears to be 3M DP420 or DP460 (very similar specs, but different cure times) Getting the correct bond line gap is very important for strength of the joint, for tube into tube application the most popular way seems to be glass beads mixed into the adhesive. Google “bond line controller”. I know very little about actual carbon tubes, so no advice from me.

  3. #3
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    Hey, even that is very helpful. Pretty much starting from the bottom when it comes to carbon.

    I'm stuck out of town for work for the next few weeks, so I've got plenty of time to read up and research before I even think about making anything. Thanks!

  4. #4
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    Plenty of time, you say? Read through my old threads in this subforum. You'll have a LOT to read.

    If you want a more condensed jump off point, here's some fun google terms (often to be prefixed with "carbon fiber")

    "micro fracture during handling"
    "debulking"
    "water absorption"
    "epoxy sizing"
    "circumference stress"
    "closed shell molding" vs "vacuum bagging" vs "bladder compression molding"
    "caul plates"
    "vacuum bag intensifiers"
    "epoxy bubble nucleation sites"

    The main scary thing about carbon is that it will (more or less) flex within its performance envelope seemingly forever, but one bad bounce beyond its limits and it goes kablooie. Like you said, the performance advantages are tempting. But holy @#$* is it ever complicated.
    Disclaimer: I run Regular Cycles (officialy in 2016, functionally in 2020).

  5. #5
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    Also if you read any comment by the username compositepro (he has posted on other sites unrelated to bikes as well) about carbon fiber, you listen to that dude. He knows
    Disclaimer: I run Regular Cycles (officialy in 2016, functionally in 2020).

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    Also the stuff Cord said about bond gapping at a just-so distance is legit! If you read the technical docs by 3M, they give a (narrow) operating range. They also give a "good, better, best" advice for metal surface prep. It's like a ton per square inch of lap bond (shear) strength or something STUPID strong like that.
    Disclaimer: I run Regular Cycles (officialy in 2016, functionally in 2020).

  7. #7
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    Drew,
    this is exactly the kind of thing I was hoping for.
    My current job is mostly sitting around, followed by a few minutes of inspections each day. SO yeah, plenty of reading time. haha.

    I'll definitely keep you in mind. May have to send you a question or two as I progress along with all this.

    Seems like the engineering involved to achieve the ideal flex/strength/safety ratio just may not be worth it (or possible with my resources). But I'm not giving up on it yet!

    I was even brainstorming of one day rigging up a test for a few handlebar mockups, charting the weight/deflection and so-on with a "real world" setup. Then testing to failure is always fun. But eliminating (controlling) variables and gathering useful data will of course be the tricky part. I'll definitely post that as well if I end up trying it.

    Thanks again!

    -Ben

  8. #8
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    Quote Originally Posted by Ben.land101 View Post
    Seems like the engineering involved to achieve the ideal flex/strength/safety ratio just may not be worth it (or possible with my resources). But I'm not giving up on it yet!
    You have a winning attitude. I mean, consider my situation where I'm *just* getting to a point of being confident selling these things after many years of learning. And even then, are my results really going to compete 100% equally against entire teams of engineers, gram for gram? Nope. In that notion, consider the Pareto Principle (80/20 Principle) for inner peace if you choose to spend some $$ on learning about this.
    Disclaimer: I run Regular Cycles (officialy in 2016, functionally in 2020).

  9. #9
    pvd
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    Obviously, I have a lot of experience here, as mentioned. Good and bad.

    Working with carbon is super easy. It's kinda a joke when you are working with 'as supplied' tubes. That's not the problem. It's the engineering. That's where mistakes will get you.

    The reason for using carbon instead of a fully fabricated bar is for flex. You want as much as you can get.....SAFELY. Fabricated handlebars are really terrible without the use of carbon. Making a mistake with carbon in this application is potentially deadly.

    We never figured out what led to the bars failure. Wheel first or bar first. Regardless, there were splinters. That's not good. After looking into it very deeply, it was determined by myself and several carbon experts that while I may have been within the working ability of the particular tube I was using, there just wasn't enough safety factor for that type of layup.

    I did a lot of work in the shop testing flexure of various layups and building a database and 'approximation' of modulus of elasticity for several layups that allowed me to compare to metal counterparts. This was a lot of work but it was important and what I should have done in addition to lab testing prior to betting on black. Still, ship sails at 4 and I was going to be on it.

    The result of this was to switch to a completely different layup, different filament, and epoxy (I believe). The problem was that this wasn't as flexible as the original material. That's not desirable, but this is off the shelf material and I needed something safer.

    I cut out all of the old material and replaced it with the new on everything that I'd done. Since, I've had no problem at all. That includes riding full ridgid like and enduro bike and the enduro bike like...and enduro bike. I feel that it's vetted...but I haven't put it in the hands of a real canyon hucker. The bars don't feel as nice as before but they still aren't as bad as steel or ti bars are.

    There you go. Easy as pie as long as everything is right before you order material.

  10. #10
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    What do you want the setup to do? Is it so you can play with increased sweep and / or use it for almost "direct mount" short stems like PVD?

    If so, would it be an idea to start by cutting in half an existing flat carbon bar from a trustworthy manufacturer rather than using random guess tubestock?

    Someone else has already worked out the layup and flex, got it to pass fatigue tests and put sufficient reinforcement in the middle to withstand a normal clamp on stem. Provided you are bonding onto that same region, then the bending moment and stress concentration points are going to be in similar places to the original setup - so your bond is the main unsafe bit :-) ......

    I can think of some drawbacks - there are probably many others
    1)Working around a small amount of pre-existing sweep.
    2)Having to use larger than needed steel tube for your "stem" part (i.e. nominally 31.8mm bore).
    3)Would there be enough bond length or do you have to encroach onto the area that wouldn't normally be clamped?
    4)Cost (depending what bars you start with) I'm thinking something cheap-ish from the big risk-averse OEM players like Giant or Pro (Shimano).

  11. #11
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    Ya know, I should've put this in the original post, but yeah. The goal of all this is to get the fit I want (being able to make super short stems, play with sweep, etc.) Which makes designing the bike around it much easier. Opens up some opportunities that are difficult to get with commercially available stuff.

    And to get some nice flex for bumps/comfort sort of thing is a very nice bonus. Almost anything is gonna be better than the super cheap and stiff aluminum bars I've been running forever now.

    With that being said, I've still got some time to get all this sorted, and i'm most likely gonna be doing a bit of my own testing as I go along. I'll definitely keep you guys posted, and put up all my tests/findings on here.

    Also, using commercially available bars to modify like you mentioned is interesting. Lots of drawbacks for sure, But you've given me another thing to brainstorm for a while.

  12. #12
    pvd
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    FYI,

    I've been designing with a 9 degree sweep for performance bike (785mm) and 16 degree sweep for the wider (820mm) klunker bars.

    I'm working on a performance full suspension bike right now and expect to build with a 12 degree sweep (785mm). Not sure if that will be right but I'm finding that 9 degree is a bit flat in my old age. Riding the 16 degree is really nice but might be a bit much when I really have to catch my full body weight.

  13. #13
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    You might want to consider starting with titanium tubing so you don't have to puzzle out anisotropic behavior.

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  15. #15
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    Quote Originally Posted by pvd View Post
    Obviously, I have a lot of experience here, as mentioned. Good and bad .
    I’ll ignore the bad, cos like my old boss at work says “if you’ve never scrapped owt, you’ve never made owt” And life is a learning curve.

    I’ve made a fair few wheelchairs that were carbon tube/steel lug, but I just used what I was given. I’d love to be able to work this stuff out for myself, where do you even start? When you say lots of experience, have you made bars using lots of different tubes? Have you done some sort of testing to compare them? Was this chasing ride feel? Or just bar position? Is it as simple as just wall thickness? Where does diameter come into it? How much effect does weave direction have? How do you calculate for that? Presumably method of manufacture of the tube has a huge impact, how do you calculate for that? What about the actual raw materials the tube is made from? How do you calculate that? Does fatigue life come into it? How much flex is good/too much? How do they compare to traditional steel/aluminium bars?

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