Hi guys,
First off the rear legs, I've had some doubts about welding them for a few decades now. Bottom line is that if your day job is welding springer rear legs into the lower tree then fine. If it isn't then you're opening a whole can of worms that can be left firmly closed by clamping the rear leg in the lower tree.
Seen quite a few broken springers (and some of them just broke in normal riding) and that is always where they break, right where the leg is welded to the tree. There's a whole load of things you can do to reduce the problem, true enough. But two things to think about, clamp the legs and you don't reduce the risk of a problem, you remove it, is the first one. Second one is that when some pratt in a car pulls out in front of you and you poke the forks into their door, which would you rather be doing? Dropping the rear legs out of a clamp and replacing them, or making a whole new lower tree as well as the legs?
You're going into production then fine, weld them. You're screwing around in your shed making a set, clamp 'em. Sugar Bear, who probably makes the best springers in the world, welds his. But then he's been doing it for decades and frankly it stops the idiot customers from screwing up the carefully worked out geometry.
Bear's got a completely different set of considerations from a home builder though.
Geometry, because the bottom rocker is usually fairly short then it describes an arc with quite a tight radius. This means that as it goes up and down there's a fair bit of fore and aft invloved. When it's coming up to the horizontal the spindle is moving forwards, trail is shortening, when it's moving upwards away from the vertical, trail is getting longer. That's one thing.
The other thing is that you don't have this problem with the rear leg. To keep the spring rate something like constant, in an ideal world a line through the pivot on the rear leg and through the pivot on the spring or front leg would be at 90 degrees to the rear leg in the middle of the travel. This minimises the nasty rocking motion in the spring leg and helps keep the spring rate something like linear.
But, the line from the rear leg pivot to the spindle really wants to be horizontal at rest with the suspension loaded, or running slightly up hill from the rear leg to the spindle to keep the trail changes sensible.
So, the chances of all three holes in the rocker being in line are pretty remote, and the ideal position for them is going to vary with the rake of the rear leg.
Brake mounting, well that's easy.
http://www.thefont.pwp.blueyonder.co.uk ... _brake.htm
Well easy to say.....
Briefly touching on girders, yeah the unsprung weight can be higher. But to counter that you don't have a lot of problem mounting coil over dampers on them. Even better girders are as stiff as buggery if their done half right, don't need weird brake set ups, and are relatively easy to build so that you get fairly consistent trail out of a set.
I guess the bottom line here is that you chaps already have the goverment on your case, so the last thing you really want is a rash of snapped off home built springers. If you see where I'm coming from?
You see quite a few "How-To Build your own Springer Forks" posts on the Net. But I've yet to see one that started off "This is how I built the springers I've had on my bike for the last 10,000 miles (16,000 kms)..." it always seems to be "This is how I built the springers on my bike/trike that I haven't finished yet...". Which is a bit interesting......
I'm looking foreward to seeing them 
