Cupcakes fabrication

Are you sure you want to put rival on this (so you have to use gxp bb's)?

You can used regular 24mm BB's with an adapter for gxp

It's a good question.

I have a few reasons for using steel on this bike for the forks, and they're understandably personal to me.

Sustainability and permanence

I want to avoid using materials that are lifespan-limited and non-recyclable. That is, on this project. I have other bikes with carbon forks, and they're great. But this is something I'm making which I hope will last for a long while. I have a frame from 50-60 ish years ago and I'm happy to ride it regularly, but in 2073 will someone be happy riding a carbon fork from today? I figure not.

Structural characteristics

Steel is adequately stiff, light and strong. There's an argument for reducing weight by using carbon on a bike which is overbuilt elsewhere, and is ridden in a very physical way, e.g. mountain or gravel. But on a bike primarily for use on the road, I don't feel it's warranted. Also, the bike industry hype around "stiffer is better" is just marketing fluff.

Aesthetics

I think a steel fork looks good combined with a skinny steel frame. It's just my preference, and I also like the look of steel&carbon together but when I thought about the aesthetic for this bike, it just feels right to me for it to be steel-forked.

Novelty

Apparently -- according to the instructor -- we can make this a flat mount disc fitment. This is pretty unusual and in my eyes that makes it kinda cool.

Learning

I'm doing this project to learn how to braze bike stuff. So, making a fork allows me to experience brazing a lugged fork crown. I'd probably not attempt this on my own as the fork is a critical point for failure, and the integrity of a fork relies on good fabrication (e.g. as I understand it, if you mess up a lugged crown it can look fine but in reality have very limited penetration of filler into the joint and thus be unsafe to use). That said, I do not in any way expect to be a framebuilder after one course - but if I can get some tutoring in multiple ways of joining tubes together (fillet brazing, lug brazing) so much the better and more interesting for me.

In fact I don't mind GXP in practice, although I consider it to be a good way to burn through multiple BB bearings in a short timeframe.

That said, I've been offered a chance to get hold of a 105 hydro groupset at a good price so will likely be going with that.

I need a solution for the cranks, however, as the groupset available to me uses 170mm cranks but I prefer 165, so I may just use a sram chainset from my parts store. If I'm totally honest, mismatching components in a way that slightly ruffles the feathers of purists is appealing for some reason :)

Nicely justified. Is there an argument for curved forks for comfort? Or is that just perceived. Maybe that benefit disappears with the extra strength needed for discs too. Or maybe I've been browsing too much Thorn pdf.

Also a good question. I'm happy to hear justification (actual engineering justification, i.e. published papers or textbooks) comparing the deflection of curved Vs straight cantilever beams. The reality is I don't know if there would be any appreciable difference in stiffness. My guess is that it's the cantilever nature of the fork that dominates the stiffness and that humans wants to perceive the curved blade as more compliant because it is literally in an exaggerated deflected shape as you look at it.

Edit: the above assumes all is equal in material stiffness and geometric cross section for straight and curved fork blades, and that the rake is relatively small.

Clarification: I'm using straight fork blades because I think they look nice, no other reasoning

Square taper bottom bracket and a sub compact chainset works very well.
Looking forward to progress.

Here's a bit more progress and designing-out-loud.

I have asked @Tijmen to make some bags for this, as I am very happy indeed with the ones on my gravel bike.

I am really intrigued by the mini rack-bag setup used by Tomii cycles on their Canvas / Fat Canvas bikes. However this is likely a step too far for my upcoming course, as I won't have time to pursue making a rack as well as the frame and forks. I plan to add some eyelets so that I could go down that route in the future.

In the meantime this led me to some thinking about which bags are actually most useful, and my conclusion is a combination of the classic half-frame bag and top tube feed bag. I've mocked up a render of these.

Also shown is my plan for a stainless cable rub bar on the headtube. Also, internal rear brake routing is on the wishlist but may or may not be practicable.

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I need a solution for the cranks

Cool build, i might have either a 5800 or 7000 165 compact available should you want to match

Also, internal rear brake routing is on the wishlist but may or may not be practicable.

How would you go around the BB? Even with a T47 BB I found you need quite accurately drilled breather holes to have enough space for the hose to make the bend around the BB.

:)

Seem to be pretty short stays for those clearances?

Cheers, that could be intriguing. 7000-series cranks are available new but not from the distributor at the moment; I think I saw some shops with stock. Let me know anyway.

How would you go around the BB?

I'm intending for the hose to exit the DT on the NDS side, then be external along the chainstay. Routing it inside the BB and along the chainstay does look great but it's too much hassle to make and install/maintain.

Same length on my Varonha, fits 38s and guards comfortably.

pretty short stays

Probably a little bit optimistic. However I am considering scaling back the clearance requirements to 700c x 35 + 45mm guards; 700c x 42mm without guards. The final rear triangle fit will be based on a 1:1 physical model over a plan drawing. We have Zona and Life pre-bent stays to try, and the dimensions will be what they will be to make it all fit together. If that means an extra 5 or 10mm length compared to the drawing, so be it! That said, my gravel bike fits 650b x 57mm tyres with a 415mm chainstay, but that required some substantial custom-forming.

Edit: or maybe it's all good as drawn, thanks @jontea !

Really looking forward to seeing what comes from this!

I agree, straight blade forks will look great :)

Sent you some details

I use steel straight-blade forks on many of my road bikes - here’s some inspiration;

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I am a sucker for a straight tapered fork.

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Started the course yesterday. Plenty of practice brazing laying down filler on a flat workpiece, then managed one test tube joint, which is of course looking far from where I'd like to be. But also I had the fear that I would really struggle with the hand eye coordination necessary, and I did find it really tough at first, so I'm very pleased with the outcome so far.

Also managed to confirm fork and rear triangle geometry. The fork will be similar to one already made by the instructor, but the rear triangle needed a full 2D plan drawing for crank, chainring, tyre etc clearance. We will be using Columbus Life road chainstays with a small dimple for the chainring.

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nice work. excited to see the final outcome.
what's the setup of the course?
are you there every day or is it one day a week or what?

It's every day for 5 days.

Got the front triangle fitted up today. Vast majority of fitup by instructor, that's their preference, means we can actually get through everything in the time available. I could do it but would take longer and possibly waste some tubes. Will look to get myself some practice tubes to try cutting mitres entirely by hand after the course. These are almost all on a horizontal mill. Also did some more practice brazing and it seems to be coming along well, so I'm pleased.

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Despite what Richard Sachs may have you believe, there's nothing to be gained by spending hours mitring with hand files

There will be some publicity photos after the course which will show the process better than I can record. I'm mostly focused on trying to absorb all the information and tips.

For sure, but I'm not likely to be getting a mill into my first floor flat any time soon. If I could just buy a house with a garage on the other hand..