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Ta da!
Right, I've been thinking about chainstay clearance for the last couple of days. I've tried heat bending bamboo briefly, with no real results other than some scorched bamboo (sorry no photos). Steam bending is definitely our as I'd like to complete it this year and waiting a month or two to dry out the stays would be annoying. So that leaves me with a couple of options. The cotswolds Jen ride is calling as a first ride!
Either Physicaly cut and sections of bamboo to form a chainstay yolk. Or, form my own chainstay yolk and reinforce with carbon . I think I'm edging towards the latter. Theres a few options with this, balsa wood or foam core to form a male mold and go from there...... But I think I'll use some of the ti tubing I bought to get the correct curves first and then work out from there. This will give me time to check tyre clearances as well as chainrings.
Right, chainstays....
As ive said above I'm building up an armature from 8mm ti tubing to get the form roughly correct.
This is now glued and milliput'ed in place. I must have spent an hour measuring and playing around with it, matching it up against my charge plug to try to get the angles correct and still be inline with the chainstays. Ive gone with a dropped chainstay design on the drive side - it's not extremely but it should be enough. This coupled with some deore cranks should enable loads of mud clearance.
Tonight the frame will come out of the jig and I'll put on the bb/chain set/40t ring and if all goes well start building up the form of the chainstay yolk around it with light weight filler. I've left the end of the ti tubing slightly long so that these can be bonded inside the bamboo chainstays.
Oh if your wondering what the offcut of bamboo is in the photo, that's approx 45mm did so equivalent to a large gravel tyre - so LOADS of room.
I've also started thinking wheels, the set I have won't fit the Lauf forks, or the rear as they are qr 130mm disc wheels from my Mk1. So a visit to my LBS (Slam69) last night and I'm ordering some hope / DT Swiss hoops. Wheels will be the only place with some colour on the bike......
Ok, quickly fitted a chainset with 40t, turns out I'd given it too much mud clearance and not enough chainring clearance on the drive side. So a quick adjustment with the pipe bender and it's gluing back up again. Sorry, completely forgot to take a photo. The weekend will be spent building the area up and then another check before more carbon fiber.
Ok, scariest part of the build - the rear end.....
You can see the chainstays a bit asymmetrical in this photo. It's the best way I can get big mud clearance at the back. 'fugly' but the rest of the bike will be a, erm, acquired taste.
And, yes the non drive side crank arm will clear the chainstay - by about 5mm.
Had to do a little more bending to get it all to fit, but I'd used my strongest glue this time which worked a treat.
Heres a photo of where I've finished up for the night. I completely forgot to sand off the top layers of bamboo on the chainstays before glueing them inplace, but thats ok as I can do that after its all glued up.
I've mounted the tops of the seatstays to the outer sides of the top tube. This will give me loads of wrapping space for carbon to really fill up the area and also it's the widest point, providing the best mud clearance. I toyed with doing dropped 'areo' style stays, but the structural down sides led me away from that.
I've roughed in the chainstay yolk, with some milliput and micro beads. The finer finishing of it will have to wait until it's off the jig as I'll nee to refit the chainset to check things again and access is poor on that side with it in place on the jig.
Much like my last build, the big question is will the rear wheel align correctly. I checked and double checked with a square, tape and by eye repeatedly. But couldn't work out if the dropouts were straight or not...... Some angles were fine, others looked out (twisted?) I'll have to check in a few days when it's a bit more solid..... All I can say for sure is that the chainstays were the correct length and everything was snugly fitted.
This is looking well good mate.
I used to use heat shrink to clamp down wraps on carbon bonded tubes. On weirder shapes I had good but inconsistant results using sandwich/freezer vacuum baggers. Making a decent vacuum set from a fridge pump changed my life...
Heat shrink is a good call, I'll have to do some googling. Not sure if/hoe that jml vacuum bagger would work on areas like the bb though... Good for small parts though.
Using woven glass fibre to separate aluminium and carbon is the normal way and a lot tougher than tissue.
Easy Composites are a good source of materials.
Could have gone down the woven gf route, but it's a bit to late now.... TBH little of the bb is now on shown and 95% is pre covered in epoxy which will/should provide enough of a barrier.
+1 for Easy Composites.
anyone looking at small scale composites should check here. I learnt so much.
https://www.rcgroups.com/composites-fabrication-210/?s=f8b4d555a0ef3e055b15b8836e6d9d31&
epoxy will absorb moisture so wont be 100% but done now. The main problem will be at edges - eg if you face the BB area you expose some carbon and some aluminium which then get connected by water and the aluminium corrodes in from the edge. Simply painting the edge or using some grease to block the water ingress will help a lot.
I guess the long term killer of bamboo bikes is moisture ingress into the bamboo and up to the joints anyway. Not that that would put me off, always fancied one myself.
For the gaps at the edge of tubes something like gorilla glue could be useful as it is a form of mildly expanding polyurethane so will be tough and expand to fill the gaps.
Zapp Pink wicking superglue solves a lot of problems.
For the gaps at the edge of tubes something like gorilla glue could be useful as it is a form of mildly expanding polyurethane so will be tough and expand to fill the gaps.
Yeah, I used Gorilla Glue as the joint 'filler' on my bamboo build.
My original build used gorilla glue, I've not needed to on this one.
Andy l - The bb will me smothered in grease so I'm hoping long term corrosion won't happen. As you say most bamboo bikes die due to the damp environment we live in, and my garage isnt exactly water tight. I can see the green fuzz of doom already growing on the inside of the off cut tubes. This is why I took Mk1 inside for the winter.....
As for easy composites, that's where I bought all the carbon fibre and glue from.so it's a +1 from me too (although postage is on the high side if you just want one small item).
Ok, just checked the frame - took it out of the jig and stuck a wheel in it.......and the back end was crooked.
But Ive worked out why. The jig comes with various precut mud spaces and block, the large 135mm spaced block which spreads the dropouts has a deep groove down the middle. I'd placed the glove up tight against the long 10mn threaded bar, however the wood was fouling the bolts of the dropouts. If you look in my last photo you can see the mdf splitting in this section - which I thought was strange last night.
Bbbc recently changed the dropout design to a modular type, hense the bolts. I don't think that theyve updated the jig design to accommodate this. I may have to email then later.
Anyway. Luckily the non drive side came away from the frame cleanly for realignment. This also gave me opportunity to sand the parts that I forgot about. After adjusting the jig so that It would'nt foul the dropouts, I've inserted a 8mm spacer on the non drive side and glued it back up, this 'should' bring things back into alignment - ill check this afternoon.
Until the wife lent it against a radiator and cracked the top tube end to end!
I wonder how the bamboo was cured? Possibly not very well? I believe in Japan bamboo will be stored for up to 3 years to turn it into timber, or you can put in at oven for a short period which is more likely to lead to cracks.
It cracked because both ends of the tube were sealed up with loads of epoxy and hemp. I hadn't sealed the frame (why I brought it indoors), so it had absorbed moisture over time and was starting to fur up. When the heating turned on in the early morning and heated up the top tube pole, the moisture in the tube had no where to go (normally it would escape from the ends of the tubes). This ended up with a rapid release of the moisture through the side of the tube, with a loud crack noise.
Shed lent the frame direct onto the rad, and buried it in cloths and stuff.....
Bamboo is kind of notorious for being prone to rotting and does have a tendency to split as it dries out. It's more likely this is why it split when subject to heat rather than internal air pressure.
It's not the internal air pressure inside the void of the pole, that caused it to crack, rather the moisture trapped in the vascular bundles within the bamboo structure itself.
Photo of the now straight (I hope) jig.
And the 8mm spacer in place.
About as straight as ill get......
Not great mud clearance on the drive side, but should be enough for 42c tyres - 35c in there at the moment.
Certainly will be..... Er...... Unique
Certainly low and slack enough. Yes, unique, that was the word that leapt to mind 🙂
It looks slack due to the lack of headset - it over exaggerates the angles.
As for unique - Slam69 are sorting me out a rather special set of 'look at me' wheels to match the rest of the bike which are being built next week.....
I do need new bar tape and a saddle....
Impressive amount of clearance. Good work.
It does look like a primary school plasticine model now that I look at the photos taken this morning! - it looks alot better now.
I aim to get the rest of the carbon fiber wrapped over the next week or so, which less daunting now that the back end is on. Just have to work out a good layup of the bb and chainstays (seatstay junction is relatively simple), I'll prob cut up some paper templates.
Bit of sanding and it's looking less fugly.
The different colours are purely because I only had black milliput left. Not sure when I'll be able to get some carbon on there, maybe by the end of the week?
Slam69 are sorting me out a rather special set of ‘look at me’ wheels to match the rest of the bike
Looking good!
An hour and a half of sticky, slippery epoxy and lots and lots of winding later......
And then when I thought the hard part was over, then came trying to get compression with the ptfe tape - due to the nature of the bb area there were loads of concave areas but 2 convex in relation to the tape, so it took two rolls in the end.
Taken the tape off the drive side chainstay, it's still slightly tacky and malleable so I'm leaving the bb junction untill tonight. Theres not enough carbon on the chainstay (used the left overs), bits of bamboo are visible in places. So this will need a second wrap at some point.
Just heard from Slam69 that the 'petrol' coloured spokes I was going to go for aren't avaliable in the correct length...... Guess it'll have to be a bit more stealth than I wanted. It's a shame as ive a few other oilslick/petrol bits I'm using.
Tapes off...
The bb is clean of epoxy which is great, but I did manage to catch, and subsequently cover with carbon, some of the Orange ptfe tape protecting that area. It's just on the edge of the bb she'll so shouldn't be too much of a structural issue.
All looking good there. Can’t wait ti see the finished build.
A hell of a lot of sanding ahead, but thats a rideable frame....
my eyes
Well it's an improvement on Mk1 😀
Lots of sanding, but it's coming along.
Clearances on the 40t chainring are a bit tight though.....
Massive respect for taking this on and getting what is going to be a great result.
i don’t know if this would be useful for future projects.
Thanks - this is certainly the most labour intensive part, and a little daunting as I'm taking structural material away - at least I can add it back in again. Having a self set deadline is helping as Im putting more time into it now.
I need to get some more of the specialist black carbon/ali epoxy for the cable guides and downtube bottle cage mounts.
Not sure if you can make out in this photo but when I wrapped the bb area I must have concentrated on the underside of the bb which is well covered with tow. To the rear of the bb and above, behind the seat tube is about 50% covered with tow and the remainder is kevlar.
So I'm doing a 2nd wrap of that area tomorrow night. I've sanded back and cleaned it up but this will need a 2nd clean up after.
Im also going to do a bit of a bolster to the seatstay/toptube/seattube junction as ill have a load of epoxy.
Also a cosmetic wrap to tge headtube. Theres enough material there I think, but also has some small areas of kevlar weave on show.
In other news other than a few odds and sodsI now have all the bits for the full final bike build. I did buy a saddle base on the wheels being rather colourful, not sure if I'll keep it now.
This is my 'to do list'.
- 2nd carbon wrap (tomorrow night)
- sanding back the carbon to 800 grit (through to next week)
- prep, prime and paint the drop outs black
- Fit the down tube bottle cage mounts (not sure how I'll do this yet (same a the seattube?)
- Following a full build, Fit the cable mounts in correct possitions.
- strip bike back down and a final sand and clean up of entire frame.
- Spray frame with lacquer / varnish etc. I'm yet to find a finish I'm happy with.
- Rebuild bike.
2nd wrap completed!
Added another 50m or so of tow to the bb area, 15m of 15mm wide tow around the head tube, and around another 30m of tow on the seattube junction.
So I'm back to sanding again, this time its less bumpy as I managed to the wrap tow a little more uniformly and compress with the tape a little more evenly. There are still high spots but not as bad as before.
Apologies for the crappy photos - taken last night in the living room with the flash on.
Im going to find it difficult to put more than 4 or 5hrs a week into the frame before Christmas as work is very busy (village Postoffice) as we are a member of staff down so I'm also doing weekends (no riding either). But I'm still pushing for a end December finished to the frame.
A bit of sanding tonight - before and after on the headtube...
Well it's getting there....
I've sprayed up the rear dropouts and given a coat of lacquer tonight - give an idea of what the bike will look like.
I've also had an idea for a head badge which has a couple of bits in the post.
First time I've put a bottle on it and it's slight out to the right, not a massive thing for me as I always carry a pump so that can go on the left.
Oh and the garage is a full on mess now.
Never mind the finish, get it built already!
(looking great btw)