You are reading a single comment by @BenH and its replies.
Click here to read the full conversation.
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
@BenH
Thanks for your kind words, guys :) I've been feeling a bit down about the whole thing for the last day or so because I totally cocked up skinning the headtube with carbon cloth (mainly cosmetic) and ended up wasting quite a lot of epoxy and cloth, but I'll give it another go in a few days. I can't wait to see it finished either!
There are a few different ways to get the seat tube to work, none of them quite ideal. Most people try one way or another to recreate what you get on a metal-framed bike - either the bamboo seat tube or a metal insert has a slot cut in it, and a normal separate seat clamp tightens it. The downside is that the bamboo is prone to cracking if you clamp it directly, and the metal insert is both difficult to glue in securely and a little ugly in my opinion. On my first bike I kind of did this, but using a clamp like this - the bottom clamp held the (unslotted and hence still strong) bamboo, and the upper clamp held the seatpost. Worked alright, but it's difficult to get an exactly round clamping area the right size on a bit of bamboo, and it came loose occasionally from expansion and contraction due to humidity.
Another option is to do a fully integrated seatpost. This is a pretty cool idea if you know exactly how long you need it, and (vitally) don't plan to change saddle, cranks, pedals, shoes or height for the lifetime of the bike.
I'm going for a middle route which I'm not entirely convinced about, but I think it's a good principle at least. The first option is out because the thinner bamboo I'm using is only ~22mm internal diameter, which no good seatposts are made in. It is, however, the size of some old stubby BMX posts, and the diameter of the thinner part on the top of those shitty plain-top seatposts. So my plan is to have the bamboo going most of the way up to the saddle (as can be seen in the pics), with a very short 22.2mm seatpost glued in the top for the last couple of inches, onto which a Brompton Pentaclip is attached to hold the saddle rails. I'm hoping that with the Brooks saddle I plan to use the metal part should be mostly hidden anyway. The Pentaclip is not a pretty bit of technology but it's nicer and works better than these horrid things. At some point I'll find someone who can CNC me a nicer one.
Like I said, all these ideas have downsides. The downside of this is that I have to have a stubby cromo seatpost from the 80s glued into my lightweight bamboo and CF frame. There are a few aluminium ones about, but I'd rather carry the extra 50g or so and not have to worry about it bending (very unlikely for such a short bit, but it would be terminal for the bike).
It is quite time consuming to write up, but I really regretted not doing it properly the first time around. Now I'm regretting not taking very good photos, but I'll want to build another one to test out my prototype jig anyway ... it's a terrible addiction!