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Discussion in 'Parallel Universe' started by ebrabaek, Jul 26, 2010.
Now to plan and scheme.
The Carbon fiber itself will withstand the gasoline without any issues. It is the resin you need to worry about. Your gonna laugh now. It is the ethanol in the gasoline that destroys the resin.... Heard that before with fuel pump oxidizing...ehhhh..??. Not really a big deal. Really. There are several chemical ..in this case gas resistant epoxy's... available. A little background on epoxy...... When you alter the composition of the polymer to resist the ethanol..... The behavior changes. It have used this.....
Again don't be afraid of the fact it is from ebay. They are a big company in Ontario,CA with their own site... It's just cheaper to buy through ebay, than through their regular distributors. When I used this epoxy to make regular parts I did not like the hardness the finished piece yielded. So what I am trying to say is.. I would not just make it with this epoxy.... But make the piece with the regular epoxy like this.....
A two piece as you mentioned.... then give the tank part two coats of the MAX GRE..... to seal the tank. Then bond them together. Will it work..... YES with no issues. It is a someone uncomfy. feeling to make something this big with the thought that it could be destroyed if you mess up..... But the important part is that you need to focus on the part that carries the word success, and focus on that. I will say this... When/if my tank cracks..... I will make a new on of CF using the above method, and perhaps yield a few more CC's of capacity. If you do begin.... Post it here, and I am sure I can help along with encouragement....
Yes....correct... But the epoxy of nowadays composition are by far better than the polyester resins of the past.
No......The vinyl ester has proven time after time to be failing over time..... More importantly.... It is of a polyester chem. composition.....and should not be combined with epoxy. It is what was used back in the 70-80's....and the reason you hear of stories of fiberglass tank's not holding up.
See post # 164, and consider sticking with epoxy....rather than polyester..... You will be glad you did.
Cheers, thank you very much.
I've been pricing stuff all afternoon. Keen to have a go at it as soon as possible. I might start out simple and work up.
Awesome...... I would not hesitate to do it myself.... To give you an idea of resin break down..... I did a plastic tank wrap on my smaller thumper with chemical resistant polyester, and vinyl ester. One area began failing after 6 months, and although the tank wrap never failed...... it would surely have leaked if it was not for the inner Clarke plastic tank. So the issues here were just fumes escaping through the poly... tank......
I do not mean to scare you off.... Just to steer you in the direction of epoxy.....rather than poly/vinyl combo's. If you click on the MAX GRE link.... he has a lot of great info regarding his stuff. The alchemist name is Gerald.....He welcomes phone calls.... If you do call..... tell him hi from me.
oops sorry for the misleading info then..
what about phenol novolac epoxy?
I was looking at the other forums and stuff that came up on google and everyone else was saying vynalester was the way to go for fuel tanks..
Actual you didn't..... Vinyl ester was what people used before epoxy...... It just did not work very good in the long term.... And the following is my take..... The chemist that developed it most likely had the formula down ok, but small pinholes allowed the gas to migrate and starting other issues like blistering that further enhanced the issue, and the results is the wobbly tanks that we saw. It is still available...... but in case you need to use it.... I would do some long term testing on it first, before making a advanced piece like a big tank. So no worries....
As far as the phenol polymer..... I have not use this particular mix.... But I am sure there are several good mixes out there. As a general note.... There are lots of bad epoxy, and with bad I mean it sets up, but don't hold up, so I always buy from the same alchemist, as I trust him and have been using his stuff since I switched over from polyester resins.
One of the ideas I had was that making a fuel tank similar to the Touratech one, but in 2 pieces like a KTM 990. Or joining the 2 pieces together for one tank, which is more problematic.
The other, possibly more sensible (if that comes into it) option is to take an F800GS rear sub frame, and build a replacement with greater fuel capacity.
Incorporate flat sides into the rear for pannier mounting, and route the exhaust slightly lower to use that empty space.
I figure, with some simple measuring and mental calculations, that an extra 20 litres from a re-designed rear end is achievable without drama. The weight is down low, the fuel pump is reused...all electrics mounted back under the seat as per normal.
So for a bike with panniers fitted, the basic external dimensions don't change at all.
The idea being, eventually, for a complete carbon fibre rear end with appropriate steel work as a replacement for the standard.
Lining it would be the best option for making sure it's fuel proof.
But it's still at the "pipe dreamin" stage.
Very impressive work.
Either method will work. There are drawbacks with both. If you are looking at a one piece construction.....Then you need to use styro foam as blocks. Then melt that with acetone after the composites is laid up. The red foam I use is stronger, and better to sculpt and shape...... but don't melt very well with acetone. The two part method is actually not hard at all. Make the foam piece.....Saw it in half..... Then cover it with say 2 layers of composites......Dig out the foam.... Bond the pieces together.... give it another 2-3 layers.... done.... Well sort of....
Cool. Thanks. I was wondering how I was going to shape it. I remember using foam a lot in construction concrete to recess for light fittings, and one square foot of foam a few inches thick seems to turn into 2 truck loads of particles by the time you've broken it all out.
I used to hose it with diesel.
The good old days....gone...you set fire to one lousy apprentice...suddenly you're a "bad" man.
I'll give the foam a try and see how it works out.
.... Yeppers.... The good old days... I have made either method..... But tends to lean more towards the two part method. That way you can make the two inner halfs with the chem res epoxy......then still coat the two halfes better with said chem res epoxy......better ensured coverage than if you melt the foam, and then "slush" the inside with the chem res epoxy. I would sure like to follow this, so if you post it somewhere here please post a link here so I can watch....
I've heard some stuff about wet setups creating parts that aren't very strong, but as you've demonstrated with you skidplate thats not always true. Is this the result of skills obtained only though many years of practice and experience or mostly just proper technique and attention to detail?
Im thinking of starting with some things for my mountain bike. Specifically the seatpost and handlebars. I'll probably start with the crankarms but they are pretty simple pieces so I don't have questions about them... Yet.
Here's the tubular questions
How can I get accurate outside dimensions? Is it reasonably easy to gauge the thickness that each layer will add?
If I start with an inside mold, (made of foam so I can acetone it away) and I get the outer dimensions right, could I build up each layer to arrive with a reasonably precise outer diameter?
Am I going to need to cut the seam on the outer layer so that its edges are flush or will a little overlap and a lot of sanding suffice to make the outer surface smooth and round?
Should I wrap the cf fabric like a roll of paper towels, round and a round, or should I cut out each layer individually?
I weigh about 160 lbs with all my gear, 4 layers should be more than enough for the seatpost right?
Would you recommend laying all the layers with the same orientation? The seatpost does take some lateral forces.
I'm not really clear on how the different types of weaves affect directional strength. I've heard that they are only strong in one direction, but the fibers are being woven in 2 directions perpendicular to each other so wtf?
What follows below is just brainstorming and thinking out loud, if you want to answer some questions I'd appreciate it, but they arent nearly as important to me as the previous questions. I really should do some research before I ask them here anyways.
Carbon fiber rims (off-road, spoke) - Honestly I will probably never make them but I like to think of the how anyways. Kind of a mental game or challenge I suppose.
Fatigue? I know carbon fiber is strong but how does it stand up to repeated stress?
Is there any way to find exactly how off road wheels are stressed? I figure I should probably take a close look at high quality aluminum rims and just (major understatement) engineer the CF rims to match their properties instead of starting from scratch.
Find out what the load/stress patterns are, then optimize weave orientations to match?
What type of Carbon Fiber weight/weave would be best?
Pre-preg? I've seen videos of people making pre-preg, if they were accurate it would be possible to make the stuff myself if needed
If I were to use pre-preg could I get away with just (another major understatement) vacuum bagging and a big oven?
These questions are a bit on the technical side, perhaps there are some links or books or something that would save people from lengthy responses. I like books
Erling, ( should I call you this or ebrabaek? does it matter?) Thank you for posting these builds, its made for a lot of interesting reading.
Erling is quite fine. My winter project is going to build a front triangle, or perhaps a whole 29 inch mtb frame with an Fox DHX 5.0 air...... But it will be featured on the FB page I posted liks to here.... Have you been there.... Lots of good stuff. We should perhaps keep the MTB talk on the FB site, as to keep this 8GS specific. That said, many answers to your questions can be applied to CF builds generally.
Thanks. Its good to know that it is the correct resin ratio and not the fancy production method that produces strong pieces (assuming all other things are done right.) Now that I think of it, in the aforementioned pre-preg video they were using a small amount of epoxy for large sheets of fiber.
I understand that I've been thinking way over my head for the most part.
2 Kevlar outer layers would stop the scoring right? Still plenty of other destructive forces going on though. I just can't stop myself from thinking that CF is stronger than aluminum so its shouldn't be a big deal, right? Wrong I know, plenty of things other than strength to consider and I don't even have a concrete idea of what these things are.
I will take your advice and focus on other things. Hopefully things that are attainable.
Now I wonder if I could make some connecting rods... :eek1
Oh another question. How much benefit do you gain from degassing the epoxy with vacuum?
That question would be easy to answer by saying... A lot... But I am afraid that might be biased towards, well.... why on earth does not all have the chamber then..??? First... The whole setup can be had for under $400 on ebay. But I build my own, as I wanted a vacuum pump made in the USA. The practical implication is a bit harder to explain, than just ease of the work. Here it is. Many of the bigger bubbles you create while mixing, will roll out when you brush on the resin, or lay in the fiber. Small bubbles.... Not so much. Then at that point, the results split. Epoxys that requires post cure, and the ones that does not. On non post cure pieces..... The impact is not too great..... a few bubbles here and there. ( this is assuming you are taking your time, and stirring the epoxy slow, and do not make a bubbly mess), but on epoxy's that requires post heat cure, these tiny bubbles will now expand....trapped, and expand as the ambient air is heated up. The following picture is of reject exhaust cone I make for MRD Racing in California.
Note from a distance....not too bad....
But a close up reveals thousands on small bubbles trapped in the matrix, and a few big ones that has popped, in the middle of curing, and created a void....
Noe with the vacuum chamber..... that problem is eliminated.
Many epoxy's are created....none equal to each other in characteristics.... They don't behave the same.... etc. so mixing temps vary...etc.... and thus creates different end results, with regards to bubbles. I usually degass mechanically, with a short heat cure ...say 5 minutes in front of a IR heat lamp, but you are playing with fire, as you are opening the doors to Valhalla, and perhaps not for a beginner. You also changes the viscosity...etc, and in my case that created another issue for me . When I degassed mech.... the now thinner resin would just run off the steep walls of the cone mold, and the first layer of fiber would lay in too thin layer of epoxy. That is a whole lot of words thrown at you from a simple question........ But as you see, it is not easy to judge, the impact, as it might vary. I will say this..... If you can afford one.... Buy it..... But as I sort of " specialize " in the garage gangsta method..... Not needing special tools, etc.... The vacuum chamber was last on the list. For you who has not seen the video.... Here it is again from my Facebook page ( High Desert Carbon Works)
<a href="<iframe width=" 560"="" height="315" src="http://www.youtube.com/embed/9sN0KT-tRsY" frameborder="0" allowfullscreen="">"><a href="<iframe width=" 560"="" height="315" src="http://www.youtube.com/embed/9sN0KT-tRsY" frameborder="0" allowfullscreen=""><iframe src="http://www.youtube.com/embed/9sN0KT-tRsY" allowfullscreen="" frameborder="0" height="315" width="560"></iframe>
I've been facinated with the process of making CF parts and read all your postings here and on Thumpertalk. Then I started building some myself! Had a few sucesses and many problems but my experience level is growing, partly because of learning from your great write ups. Thanks for all your effort. My question tonight is regarding the high temp epoxy. I'm making an expansion chamber guard and using the high heat resin. Immediately started having problems with it. It doesn't stick to the carbon!! On any of the curved portions of the part it runs off over night and leaves the CF sort of partially impregnated. And the thing is, it's super thick and viscous after mixing and when applied. I have used other resins that the carbon seems to suck up and it stays impregnated with no problem. With this stuff, I've had some pieces that I could easily pull off a part after letting it cure overnight and the CF is sort of stiff but not even hard. It also gets thousands of tiny bubbles when mixing, even if I'm extra careful. I'm doing hand layups using a mold. It seems like vacuume bagging is the only way to go with this stuff. But it doesn't make sense that it won't stick to the carbon. The manufacturer says that high heat resins are very sensitive but I'm confident I'm doing the mixing and application right. Have you had similar problems?
Ouch....... That would make for a frustrating Carbonation........ First thing first..... When you say High temp epoxy, you mean the MAX-HTE...????? As they all behave different. I will for now treat this a directed towards Max-Hte, from polymer composites. A common misconception is that epoxy's behave the same. As you found the stronger stuff that requires post heat treatment, have a few different characteristics. One is that it is thicker, by far, and because of that, you have a tendency to stir more bubbles in, when mixing. also the thicker polymer, also takes a little more to saturate the fabric. Both these issues, can be almost eliminated by pre heating the epoxy to 90 deg. prior to mixing. Bubbles is one thing, but the saturation, I will guess that you are below 75 deg, F. prior to mixing.... Which is too cold for that type of epoxy. . That will introduce a lot of bubbles, because of low viscocity, and the fabric will have a hard time soaking it up. As far as stcking to carbon, It will always do this fine. Since this epoxy does need to post heat cure, you might as well pre heat the fabric, and mould as well. So try to pre heat the epoxy to 90 deg. before mixing, and then if there is still a few bubbles in there, set the pot under a heat lamp, while you are laying this up...... Work under a heat lamp, as it will keep the mould warm, and then cure it under heat, to the spec's of the Epoxy. You do not need a vacuum system, for this to work. Let me know