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@Mikenetic
The front and back of the bike needed the most thought.
I'd originally considered fabricating the fork myself, but the more I researched, the more I realised that it wasn't going to be straightforward. Steel-bladed disc forks have to withstand an awful lot of stresses, and I wasn't confident about the robustness of what I could make with available materials. In the end I decided to use a Surly Disc Trucker fork, as it had the clearances and look I wanted.
Although there were a couple of options for the rear dropouts, I went for the set in the picture above as they were easy to get hold of and not too expensive. Plus they have built in rack/mudguard mounting points.
The design meant I ended up with a very wide rear on the bike. Alfine hubs run 135mm OLD, then you have thick sliders, and the outer steel mounting plates. All told that gets the back out to about 160-165mm. I needed to bend the chain stays to get them around the 35mm town tyres, then back in and out to get to the correct width without causing heel-strike issues.
The first prototype is in the images below. The original plan was to use straight Zona stays, then heat them to the point where they anneal (go soft), bend them to the right shape and then let them cool.
I mocked the back end up, holding stuff in place with tape to see if it would work.
The answer was "sort of". Bending the stays went alright, but the original choice of a part-sockted BB caused problems. Getting the chainstay ports the right shape & angle wasn't really working. In the end, I changed approach.
The final answer was to use a plain BB sleeve, Columbus Zona Cyclocross bend stays and fillet braze it all together. Once I'd settled on them, I bought a pair of Zona CX bend seat stays in order to get a consistent hourglass look to the back of the bike.
The rear dropouts were brazed into the chainstays. You cut a slot to allow the (shaped) tab to be inserted, then tack them into position with a dot or brazing alloy. After an alignment check you can secure them properly by heating the dropout really well, building a small pool of brazing alloy at the mouth of the chainstay, then using heat and gravity to draw the braze down inside the tube, forming a solid plug that bonds everything nice and strongly.
You can see the final result of that here. The brazing alloy is revealed when you file and shape the joint, giving a flowing transition from dropout to stay.
Trickiest part of the operation is to keep the torch flame off the aluminium dropout while you're brazing it together. You have to have the whole unit assembled with a dummy axle in place to hold everything in alignment. However, that went alright, so I was able to drop the wheel into the back end and check it looked alright.
Once I was happy with that I moved onto fillet brazing the front triangle, chain stays and finally the seat stays.