Tdotbikes

Hi everyone. I am looking at my next build, a lugged steel city/road bike with disc brakes 650/700c wheels. I have never owned a bike with discs brakes. I plan on using Llyewellyn Manorina lugs with Columbus tubing. The seat tube angle of 73, head tube angle of 70, chain stays 445mm, fork rake 50mm. This is the geometry of my current bike that I fillet brazed and like very mucho. There is nothing wrong with it but now I would like lugs and disc brakes. I am 5'9" and weigh 155lb on a good day.
I plan on using flat mount brakes on the rear and would like the same in the front. I will bend the fork blades to get 50 mm of fork rake. How does one go about attaching a flat mount caliper to a curved fork blade? Should I look for a heavy disc specific fork blade?

Andrew R Stewart 

I strongly suggest that you do find a disk worthy fork blade. Nova has offered some in the past and I believe Columbus (and others?) does now too.

I went through this very question a couple of years ago when I made my first disked bike. I decided to go with a straight blade to avoid the fabbing of a mount which will handle a curved blade in addition to the disk blade's likely being much tougher to bend. But I used an IS mount and wanted a tail running up the backside of the blade for stress distribution and blade bending resistance. I haven't looked into flat mounts and the various dimensional and fit considerations so my experience might not transfer completely. Andy

unterhausen

flat mount forks are an exercise in fabrication. You can't just buy the mounts. There are a lot of fixtures available now though.
I suggest going with the Reynolds disc specific blades. For whatever reason, Nova still doesn't have theirs and the columbus options are all unicrown.

Tdotbikes

I appreciate the comments guys. I thought that going with a flat mount brake would make life easier. Looks like I'll stick with ISO. I was thinking about running 650x40mm wide wheels with fenders. The Reynolds disc blades look perfect and I'll incorporate a long disc plate mount as Andy suggests. Just need to look for a fork crown and dropouts. How wide of a fork crown should I use if running 650x40mm tires?

Andrew R Stewart 

Everest Steel Cyclo-X Fork Crown (cycle-frames.com) This is what I used with the mentioned Nova blades. Plenty of clearance for a 38mm tire. Fairly light for its width and it feels stiff to my 150lbs, Andy

unterhausen

Note that the version that Andy linked has a 7 degree angle built in for straight blades. I like that crown, either straight or angled. A lot of people use the Pacenti MTB crown.

guy153

You could go with post mount. I think this is more "standard" than flat mount (but there are adaptors either way). You can buy the mounts and just braze or weld them on.

I have come to the conclusion that the best way to make a bike these days is to buy all the parts first and then make the frame to fit them. This saves you some of the pain of buying stuff and then being thrown a curveball in the shape of some completely new and pointless standard you had never even heard of.

I did this the last time but was still caught out. The groupset had a "swing pull" front derailleur in it. I could easily have accommodated that with a cable stop in the right place, but had already painted the frame, so had to find a different derailleur. I had never even heard of a swing pull and didn't look closely enough at the parts I had bought before making the frame.

unterhausen

So far, all brakes still come in post mount*, so you can always get a flat mount to post mount adapter. The mechanics at my lbs hate flat mount with a passion, because they are almost always out of flat and the tools available to flatten the mount are a pain to use. So they were lobbying for me to use ISO, since that always works.

*sram and shimano have some road groups that only come with flat mount brakes, but they have compatible post mount calipers.