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Bambooride
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Group: Forum Members
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Hi,
we are doing we layup with a layer of breather cloth and then compress with heatshrink tubes. That works fine, but the finish is of course the finish of a breather cloth which needs sanding. It is important to have the layup wrinkle free to get a good result. You can see some pictures at eigenbau.bike ( sorry German only)
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M Hathiyari
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Group: Forum Members
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Hi @Bambooride So After wet layup of rods how do you apply compression force to it.I am making a Carbon fiber tube by roll wrapping wet cloth and then vacuum bagging it.I have concerns that the outer finish wont be that good.Any suggestions on how to go about bagging to get a better finish?
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Bambooride
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Group: Forum Members
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:-) In a way you were right though - a friend of mine who helps me a lot with building bikes borrowed it for showing it off to his frame-bulding girlfried (yes, there are girls welding frames...) in Paris and he did ride it despite my warnings for a few days (he is a 60kg man though).
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Drew Diller
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Word. Sounds a good plan, didn't mean to insult your intelligence.
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Bambooride
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Hi, I am well aware of that - I made it so light because I didn't want to use much of the expensive pre-pregs for something which was basically a trial-run of the building process. I plan to put the frame into the frame testing machine to determine the forces where it actually fails.
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Drew Diller
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Group: Forum Members
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I'd be careful with riding that frame, 850 grams is too light weight. The lightest of the light weight stuff for MTB frames these days are less than three pounds for full carbon frames. Yours is less than two and includes some bamboo (which I like, but it is not as light as CFRP). Not trying to be a buzzkill, just concerned about your physical safety.
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Bambooride
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Hi Everybody, it's a while since the last post, but I just wanted to let you know how the story went on.... After some thinking and reading your posts and watching youtube videos of mast-making, I decided, that my manufacturing problem was the imperfect compression of the layers. I did three more tubes on 60mm, 50mm and 20mm mandrels, with 4 layers +45° each. I tried to compress the layers individually by wrapping the tube with a very strong plastic tape after each layer was put on. Indeed I could see how the material compressed, as the exccess material got squeezed out when wrapping. The results were much much better, but not perfect. Even though I got closer to a nice process, I decided that it would not be possible for my purpose (producing tubes in a seminar setting with limited time available and untrained attendees) to get that process stable soon. I might come back to it later. I went back to making the tubes with wet layup as suggested in that forum. That was straightforward and I guess will do the trick for the seminars. Anyway, I decided to make use of the messed up tubes by building a frame out of them. I did not have enough 20mm tubes, so I made the seatstay out of bamboo - also as a reference to where I'm coming from (building Bamboo bicycles). Again I used prepregs for forming the connections of the tubes. This was quite straightforward - cutting pieces of 5x5 cm or so and putting them (cleverly orientated, of course) on the tube proved to be easier with prepregs than with a wet fabric as I normally do for Bamboo bikes. I vacuumed the whole frame in the oven. The whole lug-making process was simple and the result was nice, given that I did not spend more than 2 hours on it. One one position I put too much breather fabric in the bag which removed the local pressure from a concave part of the seatstay attachement, so the uppermost layer of prepreg delaminated there when I ripped off the nylon. But that could have been easily solved with a bit more care when making the vacuum bag. Just for the fun of it we assembled a bike with that frame (which weighs 835 grams even though I used alu dropouts - it could have been 800...). As expected, the bike is ride-able but is very soft with respect to torsional rigidity from the rear axle to the steering tube. The bike feels as if it would break apart if you pushed too hard. I let it live so I can put it in the frame test machine to get some data on it.
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Fasta
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Three layers shrink tape for thicker laminates.
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cornelp
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Hi Alex, One way I found easy for tubes is to use a full heat shrink tube. This way you will get an uniform thickness. The only issues are: you need to find a tube that has no adhesive at all (the usual "battery" shrink tube is ok) and it is not that easy to take off. Usually you should heat it to about 150degC with a heat gun and you can tear it out. I tried waxing the inside of the tube before shrinking, but I do not like the embedded wax in the final product... After removing the tube, I sand a bit and apply https://www.easycomposites.co.uk/xcr-epoxy-coating-resinor a thick epoxy of your choice, but the above is very glossy and crystal clear without any yellowish shades. Cornel
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Bambooride
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Group: Forum Members
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Hi Drew, sorry for the late reply - I had actually written the response a while ago but didn't hit the "post reply" button. 1. Nice bike you've got. It's quite a funny coincidence that a friend of mine showed me a picture of your bike as he's planning to build a fat-tyre carbon/bamboo bike. My website is Bambooride.com. I run weeken-bike-building-workshops where you build your bike in a weekend. Some of the results can be seen here: https://onedrive.live.com/redir?resid=BBF286F67D81C572%21103 Since about half a year I switched from using rovings for the joints to woven fabric which is a bit harder to use, but gives a nicer appearance. 2. Thanks for the advice but I think I'll stick to aluminium as I didn not have any problems removing the mandrel in the last trial with the new release agent. --------------------------------------------------------------------------------- To everybody else (and Drew- of course) Still - I face a problem with making tubes - I tried 50% overlap and the result is much better than the first try, but still not satisfactory. I took good care to overlap the heat shrink tape by exactly 50%. But it seems that it shrink laterally as well, leading to a sprial wound "unevenness" (I don't know how to express that - but I think you'll see it in the picture. Is there a way to make a tube with perfect appearance without the need for sanding/painting? (Is using a mold the only way?) Is peel ply/vacuum bagging more promising? |
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