Bamboo Bike #2

Step 6 Seat Tube

A problem that I had on my first project was that the bamboo seat tube I used had a slightly smaller inner diameter than the original frame's seat tube.  Now this would be ok if I had a 31.6mm tube on the original bike because then I could just down size to a 27.6mm seat post and use a shim at the bracket interface.  But no...  The bike I used used a 27.6mm seat tube, and I can't find a smaller seat post than that!

So, on the new bike - the tube diameter is again 27.6mm.  So, thinking ahead I chose a bamboo tube that would actually fit over the current alloy tube a bit, so that I will not have any problems with the seat post fitting properly! 

As you can see below in the pictures I cut the seat tube and ground out the seat tube bottom bracket interface.  I trimmed my bamboo tube to match the cutouts.  Came inside, mixed up yet another batch of resin and repeated the same steps as on previous tubes.  Smear a generous portion of resin on the intersection of the joint inside the bamboo tubing in this case.  Smear alittle resin on the outside of the tube and wrap with some carbon, strategically at this point to make sure everything stays together if it gets kicked or stepped on! 

A little more detail on the wetting of the  carbon:

Initially I usually put a small dab of resin on the tube I'm going to be wrapping.  I do this just to ensure the initial bond.  I wrap one or two times loosely, crossing over the very beginning of my string.  I then pull tight wrapping one or two more times, again to ensure the string does not come loose during the rest of the wraping. 

I then take a small dab of resin, I use basically a popsicle stick for this part, and apply the resin to the carbon I've wrapped - making sure it all gets wet - all the way through.  You can be rough with this process kneeding the resin into the carbon, this stuff is strong.  the next couple times around with the string don't need additional resin as the resin from the previous application usually pushes through - and I pull everything SUPER TIGHT!  by doing this I get the same effect as vacuum bagging (kinda).  It pushes all the air bubbles out and really makes for a good bond with any previous layers of carbon you've layed down. 

Then simply wipe away any excess resin.  Come back 15 minutes or so later and see if there are any drips, if so wipe those away as well. Then let it cure - depending on temp this could take 30 minutes to 24 hours.  During the late spring early summer here our temps got above 110 degrees F.  Now it's mid 50's.  My initial project saw cure times around 30 minutes, which severly limited my layup time.  Now the curing process is at least 5-6 hours.  It's still tacky after that amount of time, so I've been letting it sit over night before I touch it again.

TIME FOR A LITTLE WARNING!

This is a true long strand carbon layup we are doing.  Each time I start to wrap the carbon I cut a string around 12 feet long or more.  It is ridiculously strong!  In addition, by the time I've layed down all the carbon - it's about 1/4" - 1/2" thick in some places.  It would take quite alot of shear force to bust one of the joints.  That said - if done incorrectly, if not OVERDONE, you stand a real chance of getting hurt in the future.  So, make sure you cross over your intersections at all joints MANY, MANY times.  It's not enough to have a pretty bike, or even a pretty safe bike.  You want a Pretty and Safe bike in the end!!!