Once the amount of trail had been determined (in the "Framebuilders" thread), I set about building the front forks. Two 380 mm lengths of 25 mm tubing were used to build these. A slot 9 mm wide and 30 mm long were cut in one end of each tube and the dropouts previously manufactured were inserted, positioned and tack welded in the slot, in one spot only. (The slots were cut using a hacksaw and filed to size.)
The fork legs were then attached to the frock motor, and aligned with each other. A short length of 14 mm tubing was tack welded between the two legs keeping them in alignment. The forks were then removed from the motor and a second tack was added to the dropouts, replaced back on the motor and checked for alignment, removed again and fully welded.
The head stem and fork assembly from the bike in junk1 were used. I cut off the (rooted) front suspension tubes, leaving the head stem and the two outriggers. These turned out to be too short and the fork legs had to bent slightly inwards to close up the gaps. The fork assembly was mounted in the rudimentary jig taking care to ensure 30 mm of trail would be used, and the tops of the fork legs were tacked to the outriggers, 2 tacks on each fork leg. The frame was then taken out of the jig and all parts were assembled. MOBILE at last
Time to test the low speed handling as this was the most concerning to me (I'm not concerned about higher speed handling - that will be fine).
A quick scoot around the backyard confirmed that low speed handling is excellent, flop is minimal and pushing the bike by the seat at around 10kph confirmed it tracked dead straight. SUCCESS
The fork legs were then fully welded to the outriggers, and not trusting the Chinese robot welding, a gusset made from 3 mm thick 25 mm wide flat was bent to the right shape and fully welded in place. Once this had been done, the frame was reassembled again and assessed: geez that looks a bit odd! To add a bit more strength and fix the odd "look", the fork legs were extended to the top of the head stem (using sleeving ...) and an upper triple-tree was manufactured.
A trip to the local steel supplier saw me score some tubing that slid relatively easy over the 25 mm tube. Also scored was tubing that slid easily over the upper steering bearing race. These tubes 20 mm long were positioned on a piece of 3 mm thick flat and tack welded into place. A hole was drilled and filed for the threaded part of the head stem to poke through, everything was checked for alignment and fully welded. To add strength to the plate, 3 mm flat was welded tangentially between all the tubes and the welds were cleaned up. Ta da, a triple-tree!
Provided the welds were not cocky-shit (and they're not), this assembly will never break. With the benefit of hindsight, I would make these slightly different next time.
Still to do: clean up the welds. Remove the 14 mm brace and make a new one that doubles as a cantilever brake mount (this one's 50/50)