Today I put the last 2 layers of carbon on the seat-tube and then finally got to unwrap all the tubes and sand back the joints and bamboo.
Here’s what she looks like now:
The only things left to do now are:
- Drill a hole in the rear bridge for caliper brakes to mount
- Bind a small amount of carbon around one of the rear stays, which has developed a hairline crack during the build process.
- Coat the entire frame in “clear coat” (an epoxy based varnish)
- Put on parts!
Today I’ve put the first of the final touches to the frame – a carved bamboo head-tube Cognitive logo. It’s a bit simplified, but that’s ok as it will probably change down the track anyway.
The only things left to do now are two more layers of carbon on the seat tube and then to unwrap all the tape, sand it back properly, and add some final clear coat as a protective varnish layer.
I’m continuing to wrap the bottom bracket joint today. I’ve now done a total of 9 layers, which I’m pretty sure will be enough for a sturdy and stiff BB.
After wrapping up each series of layers in cling wrap and PVC tape I place it inside my homemade autoclave. It gets up to 80 degrees C in there, with just a regular old hairdryer. 30-40minutes is all it needs at that temperature to cure the epoxy enough that the wrapping can be removed. It will continue to cure at room temperature over the next few days.
this is what happens when you forget to poke holes in the wrapping tape.
a hairdryer stuck into a carboard box.
The headtube’s pretty much done so I’m now starting work on laying up the bottom bracket area. It’s a much more complex shape to work with, which made the template cutting all the more fun. I’ve figured out a better way to make the templates is to wrap smaller pieces of cloth around each part, then stick them together with tape, then cut strategic slits to remove it from the frame. Then lay that all flat and trace over it to make one bigger template. I also add areas of overlap around where the slits were cut to add strength to those areas.
Here’s some pics of the finished headtube and the first layer of the bottom bracket:
Unwrapping the first layer this morning and it’s all gone well. The cling wrap’s left lots of wrinkles in the resin, which isn’t ideal, but for these base layers it’s ok as it’ll all get sanded back. Hopefully by the time I’m on my final layer’s I’ll be shrink-wrapping with better precision.
I’m now onto the 2nd and 3rd layers. Each layer I’m making from a slightly smaller template so the edges of the carbon fibre will gradually taper off rather than being a sharp drop off to where the bamboo is.
You can see the wrinkles left by the cling wrap
I finished off the rear end with some tow wrapped around each stay
The templates get gradually smaller to taper the edges
So tonight I’ve started down the road to the final wrap. I didn’t document last night’s fibreglass layer, but it’s very similar to this process, just with white fabric instead of black. The layer of fibreglass is used between any steel parts to prevent the carbon fibre from corroding the steel (that’s a very long PDF on the topic, probably best you don’t click that link).
So, with an array of carbon fibre, some dish cloth and a penchant for late-night carbonfiberizing I got stuck into it.
First I used the dish cloth as a template around the joint I was wrapping (in this case the head tube). The idea is to use as long a piece of carbon as possible without cutting it. I managed to make something that looks like a space invader. It’s done the job splendidly thou, with very little overlap and good coverage around the awkward tight areas. The comments within each picture explain the process.
dish cloth isn’t as conforming to 3D surfaces as CF is, making this quite hard to do.
Dish cloth spaceinvader template is ready to attack
A glorious expanse of CF
There’s 12 thousand threads inside that twine. That’s a lot.
Good for winding around joints and laying lengthways along beams
Just used a straight rule and a scalpel.
The finished cut out CF, ready to be stuck to the frame
A layer of cling wrap, followed by tightly would PVC tape keeps it all in place
Same thing different angle
I’ve cut, drilled and notched the seat-post sleeve and epoxied it into the seat-tube. Hopefully the carbon fibre will arrive tomorrow and I’ll start the mega-sisal-carbon-bamboo composite process!
I’ve completed the wrapping of the drop-outs with sisal. I’ve also added stay support bars near the bottom bracket and seat-post to give the frame more stiffness. Here’s some pics:
The clearance between the last cog and the chainstay wasn’t something I thought about that much. Luckily for me there’s about a 3mm gap to spare. This will be a single speed bike, so there will be plenty of room anyway.
The chain tension screws were also a very close fit. I actually had to cut away at the joins a bit to make them screw in properly.
Started wrapping the sisal twine around the joints tonight. Here’s the process for the seat-tube. I’ve done it in two layers. The first using lengths that run lengthwise down each pole, following the curves of each filleted corner. The second layer then holds these strands in place by wrapping around and around them. I finish it off with a few diagonal turns across the main joint and give it a haircut to neaten it up.
There’s no epoxy on any of this. I’m mainly practicing the wrapping process but am also considering making some sort of mould that I could then inject the epoxy into the sisal and joint as it is now. I’ve tried brushing and drizzling epoxy into twine like this before and then wrapping it in PVC tape to set and it sort of works, but due to the tightness of the wrap and the double layer it might need more pressure than what PVC can provide in order to make its way to the bamboo and not have any air bubbles in it.