KasbeKZ

circumstances and curiosity have got me dabbling in the cf build deal. i've been searching a ton and learning a lot on it, but a few questions remain. i'll just pack them in one thread so as to not hog the forum, and list them in order of importance to me, or in other words, in order of decreasing cluelessness in which i am currently in on it.

1. best weave. every build story i read recommends a different one. i'm not looking for the very best per se, but the one with the best blend of benefits i.e. cost, weight, strength, ease of forming, ext. vendor sites have got me on 3k twill weave weighing in at 5.2 oz. it's fairly affordable. good bet to use for the entirety of the structure? should i get a unidirectional to put on the tubes?

2. metal parts, namely the bb and head tube. most build stories i read just skip casually over this part and say that they "had one machined". are there finished tubes that i can get to build right into the frame? i see no reason to get a raw tube and have it machined to my needs when i could easily get a finished one and build the bike around that.

3. finally, layers. i'm a pretty big guy at this point, weighing at about 220, so i'm not sure i want to build a bike just like some competitive racer weighing 150 lbs did. on one side of this argument, i could take someones advice and go with a pre-determined number of layers on each part (10 on the tubes, 15 on the stays, extra 5 on all the joints, ext.) and maybe add a layer all around, or, considering that i'm not looking for a super high performance light weight machine, just a fun project and a good frame, i could just keep adding until i've reached roughly the same weight as the aluminum frame that i'm modeling it after. granted, i do accept the lack of R&D that i'm going into this with, and that really the only way to find out is to test. but if someone has experience that can help me, i'd love to hear it.

thanks in advance everyone.

NoReg

I'm a boat guy... But... it makes a huge difference if you are making carbon tubes, or are using carbon without form restrictions. Tubes are not a very efficient method for carbon, but more importantly you have to be able to handle all the radiuses and tight corners.

I wouldn't worry too much about perfect. Just use what others are using, but keep in mind basic principles like tow and uni are more efficient, often much cheaper, but harder to handle. Twill is also directional but more easily molded, etc... I would highly recomend starting small and making something that is not as large as a bike or as complex, and getting a little lamination experience, if you don't already have it. In this internet world, people bit off huge projects with zero experience, but it isn't the zen way. Better to build up to it a little...

If I was alone without the internet etc... and had to make some scantling decisions, I would note that carbon often ends up one half to 1/4 wall thickness of aluminum in the parts I am familiar with, like spar tubes etc... If you look at the tubing wall thicknesses of aluminum tubes for bikes I would conclude that the main restriction is going to be making tubes tough enough not strong enough, that means wall thickness is more a firmness issue than big structural analysis about whether it busts. I say that because if you take half the meat ouf ot an Al tube conversion it is a pretty thin walled tube. Just my guess though.

Aluminum bonds well to epoxy in this kind of ap. So I would be inclined to source head and BB from Nova Al tube sellection, Of course it will be oversize, but in both cases that means just tunirng down the exterior, or eating the mild excess weight.

Don't cheap out on the resin. Carbon parts need high performance resin systems. It's the concrete where the carbon is the rebar. Both need to be up to the same gig. You can use low quality resins but not if you are building efficient structures.

KasbeKZ

thanks much for the reply! i also come from a boat building back ground. my dad and i have both worked at Zimmerman Marine (VA) (i mention because it's often mentioned in articles in national magazines), and my dad for close to 14 years now. i spent a couple summers there. on a side note, if you go to the website, you'll see the heaven 12.5 meter that my dad is currently building. it's a great project to watch! neither of us have ever worked with carbon, but are no strangers to both fiber glass an ingenuity, hence my optimism on the project.

i appreciate the suggestion to start small, and i may do so in a non-practical manner, meaning, just perhaps building a plain tube and testing it a bit which i believe could greatly improve my understanding of what i need to do.

i've come up with a tentative idea for the metal bonding. i expect that if i coat my metal parts with a smooth coat of g-flex and let it kick, i'll be able to simply start gluing my project to the tube with much less worry. i've heard of people using etching primer or something of the sort, but g-flex is relatively new and i've heard great stuff about it. dad says they use it a ton at the boat yard.

do you say that carbon is not so great as a tube because it's better when ob-longed or made into a shape with corners? or that it's not so easy to use in a spar type setting? i'm planning on doing this monocoque style, or however you spell it, so in any case, i'll just be using too much material everywhere to make up for structural soundness. weight is not a huge issue in my first go around. as long as it's not heavier than my existing bike, which is not saying much.

for resin i was planning on using strait west system. many have success with that, and i can get it cheap through the boat yard.

thanks again for the response, and i understand the lack of optimism, as i often have in similar situations on the internet, but keep in mind, i'm a very reasonable person who is not 100% committed to this idea yet, so i may decide against it at any point. i'm getting closer to that point too, as i've realized that i'll need to budget upward of $450 for this project. i could buy a complete bike that's better than what i'll end up with when it's done for that. so i'm not sure. i think the experience may be worth it. but if my frame turns out too heavy or too weak, it could be just a huge loss! i'm still doing my research though. thanks again.

NoReg

I'm perfectly optimistic for your project, just not so optimistic about my advice giving.

Roger on the WEST, in fact if you can get WEST cheap you are officially my best friend!! WEST Tech support is top notch. If you want to find out how best to bond to metal just call them if you have free long distance or try an email. G-Flex sounds like a bad bet to me. It is flexible, but is that what we are after here? (though I should point out the absolutely massive bonding area available over BBS and HTs probably means most things will work). To bond to aluminum in situations where the aluminum is enveloped, I just coat with resin, then sand the resin and the metal and just go ahead. That would certainly work, but there may be better methods. WEST as you know is a big exponent of hardware bonding, and the prep there is pretty minimal. Etching sounds like a good idea I kinda figured sanding in WEST was not going to let oxide come back at all. While no mater how you clean aluminum the oxide is back pretty much instantly which is the why behind AC welding and flux welding Al. If etching gets you there that would be good too.

Tubes are an incredibly weight efficient way of building a rod, but what the bike wants to locate in space is too complex for that model. The diamond frame is completely awesome for what it is, but there is also a degree to which it is like a skin kayak compared to a fully molded one. Anyway, I don't mean in the least to disuade you from building with tubes, just saying you have to deal with all the issues differently if you are going that route. If your frame is tubular rather than like a jelly bean etc... it will need different approach which will ultimately have some effect on your cloth selection.

By the way, check out bamboo making threads, blogs those often involve joining bamboo tubes with epoxy and carbon. And:

https://www.calfeedesign.com/

There are a lot of cheap carbon tube makers out there so it might make sense to start with that. For that mater WEST did an article on tube making recently, though I seem to recall they were mostly braided. Check out their Epoxyworks. There are some interesting tube videos on YT.

I don't find working with carbon all that different than working with glass. The stuff floats up a little, and it is opaque so you have to work carefully since you can see trapped air as easily, etc..., Carbon nudges people, at least in boat projects, to go all nutty high tech, so they start out building a ply dory and before you know it they are buying resin infusion planing software.

Structurally carbon is a big difference. It isn't forgiving. Very many carbon products have started out with models that broke, and that took a fair while to stabilize into something that was durable. I have seen the wars on fishing rods, arrows, now bike forks, etc... In the end these products often end up being the most durable in their segment for a variety of technical and marketing reasons, or not. Carbon lures people into making very light structures or into creating unexpected stress risers. Be careful with sanding, or any uneven surfaces that cause spikes in localized structural features. When making composites always remember what will stretch more than what, when you can share loads and when you can't. So imagine you have an elastic and you decide to strengthen it with a strong thread. The thread will not give so it will load first, and fail, then it is all up to the elastic. That is how carbon often behaves when bonded to something else. People figure they will share loads but the fail in sequence. Makes it sound complex, but there are a lot of people doing home projects with the stuff. I'm just rattling off the various things that have led to parts that went "bang" for me.

By the way. Ajax cleanser was apparently originally designed to clean aluminum surfaces for bonding aircraft parts. It does a good job cleaning.

KasbeKZ

thanks much for the response. i'm surprised you can't get west just as cheap since you're in the boating industry. if you know someone that works at a yard, or you work there, prices on paints and materials like west are typically half price. i just painted a boat with awlgrip and paid $40 per quart of color for something that is advertised near $90. i'm not sure about the g-flex. i hear it's great for bonding unlike materials. i'm not so worried about the flex because my tactic would be to put a very smooth coating of it on the metal tube just as a barrier between the carbon and the metal. btw, g-flex is a west product. though, this may be what you are talking about in your second to last paragraph. if the g-flex did flex the slightest amount it could break the bond with the epoxy holding the carbon to it. thanks again for the response.

NoReg

On the G-flex, I have some, know it well. In your original para, you say:

"'ve come up with a tentative idea for the metal bonding. i expect that if i coat my metal parts with a smooth coat of g-flex and let it kick, i'll be able to simply start gluing my project to the tube with much less worry. i've heard of people using etching primer or something of the sort, but g-flex is relatively new and i've heard great stuff about it. dad says they use it a ton at the boat yard."

I didn't get from that why you are using it other than you think it might be good. I figured you were either concerned about enhancing adhesion or the possibility that the different expansion rate of materials might fail the bond, and G-flex being flexible would deal with that. In your most recent post it sounds like you are worried about galvanic? It would help if I knew what is the issue. My assumptions are:

- That a flexible layer is not essential, there are many products where carbon is bonded right over aluminum from mountaineering ice axe shafts to Olympic archery arrows and while the materials are dissimilar there does not appear to be an issue of some kind of shear induced separation as a result of dissimilar materials.

- My assumption is that G-flex does not improve the performance of carbon when used as a boundary layer for adhesion, and this is sorta anti WEST with all their performance emphasis on the need to have hard epoxies. But that is just my guess, and it could be a good question for their techs. In part I am just relying on the idea above that there are lots of product that work well pre-G-flex. Should be easy to source g-flex stats on bond strength.

- On the corrosion issue I rely again on the idea that it doesn't seem to be a problem, particularly on dry land, but then suggesting that you prep the surface with epoxy can't really hurt anything. But if it were me I would be prepping with 105/205. Again, the kind of question you could ask their techs.

WEST, got off to a good start with the wood epoxy thing, and promoting epoxies that could not be formulated (like g-flex) as 1-1 mixes. They emphasized hardness and creep resistance. While I believe they were right in that, they left themselves open to competitors who have hammered them on the "fact" that their epoxies are too hard, and crack etc... Nonsense, but it has gained currency. However, there are applications where the durometer of their epoxies is too hard. If you look at this aluminum bonding video, you can see that they are selling G-flex as an improvement over silicone caulking. Obviously it is much tougher than silicone, but something like oil canning in a boat plate could break out a hard epoxy, while silicone would not have the adhesion or penetration or durability of epoxy.

https://www.westsystem.com/ss/g-flex-demo/

Another example from their info is a guy who used g-flex alone to bond guides to a fishing rods, without using thread whippings. This is an interesting case, because the carbon fiber rod blank would be a very poor candidate for g-flex lamination but the extreme deformation it is capable of creates a micro environment where just gluing guides onto the blank with hard epoxy might not be successful.

I don't think you will run into trouble with what you are suggesting because there are many square inches of bonding surface on either of the tubes one needs to bond. I have bonded many golf club heads to shafts with specialized golf epoxies that are 1-1 mixes. Some of these have proved brutal to dismount, in one case requiring so much heat the thing went off like a Roman candle. In these structures (tube inside of tube), the bonds tend to be very reliable.

KasbeKZ

ok. that's interesting info. you've got me in the school of thought now that if everyone else bonds to aluminum with epoxy, then i should too. i was thinking g-flex just so that it would bond to the aluminum better than plain epoxy. i guess with a non-flexible joint, this is not an issue. i had expected the g-flex to serve the purpose of corrosion prevention at the same time.

thanks again for your response!

Canaboo

When working with composite materials the build up in strength can be quite massive.
Even if the initial g-flex bond is too flexible you have to remember it's going to be encased in a block of much harder material.
This is why tack welding with a 5 or 15 minute Epoxy still works well.
I'm not sure how people can say WEST is a brittle product though. Let a pot of it flash off and try to break it with a hammer. It won't shatter.
I would also add that etching is your best bet for a good bond and it never hurts to use a single layer of glass cloth as insulation between carbon and aluminum rather than a resin layer.
I always rough up the Aluminum aggressively with a coarse grinder and stipple the surface as well with a drill. Just going over the entire surface and creating a series of shallow recesses to allow further keying in for the epoxy.
You will note that BB shells sold for carbon bikes are extremely grooved for this reason.
Even the best bond between Aluminum and Epoxy is not very good. The best out there is 3M DP460. It's probably twice as strong as the next best.
I will also mention that anyone who has done an aluminum Epoxy bond has stated that it will always eventually fail unless you etch it first. Even if you "wet sand" the surface with Epoxy. Why take a chance.