I painted up Jason's frame quite a bit ago and have been awaiting both time and materials to complete it. Jay had desired a Ti fork to complement his new ride, but I honestly have not been impressed with the performance of available Ti forks in the past, most sacrificing durability and real trail performance for light weight. I wanted to create a piece that was stiff enough for real trail use, tracking well without annoying flex and loss of steering control. The unicrown design I created would maximize the surface area of the leg/steerer area, supporting the fork for both fore/aft flexion as well as lateral stability. A constant radius leg would limit brake shudder and allow me to anticipate the amount of fork movement under stress. The only hiccup was that the diameter and wall specs I wanted did not exist. That meant that I had to find a source for custom tubing without a huge minimum order. As I've worked with Joe S of Titanium Joe alot for bar and frame material and been pleased with his customer service, I pulled the trigger on the supplies. With a custom order of tubing in the works, it was up to UPS to finally bring the final bits home. Now 12 weeks later, the supplies have all arrived and the work begins...
The first order of business was to create a new fixture that would locate and hold the leg pieces of the fork for mitering. As the unicrown fork has a compound miter, a cut that allows for fitting of the legs and steerer pieces together and creates the offset for the eventual rake of the fork, the fixture would need to allow for simultaneously cutting of both legs for symmetry and the ability to change the variability of the angle where the cutter meets the material. I also needed the fixture to allow for in phase mitering of the dropout end of the legs, so that there is as little variance in the fit as possible. With the design goals layed out, I made a trip to my local Al supplier and I began to machine up the pieces...
The process begins by finding the exact numerical references of the piece and locating the origin points. Here I'm using an edge finder for reference...
I'll use these points with the digital read out to help me set up the piece before cutting. Once in place, I can begin machining...
checking it against the plans..
working on the vice interface...
and through the magic of the blog, we fast forward to a dry run fit up to see that the fixture is put together correctly and works as expected on the horizontal mill...
Happy with the fixture in it's abiltiy to hold the pieces securely during mitering, offering the necessary adjustability, and ease of repeatability, it's time to start working on the ti fork.
I started off by cutting the material to it's rough lengths in the cold saw, a tool that flows liquid coolant over the material and runs at low rpm's so as not to heat or temper the tubing.
The tubing cut to length, it is then deburred, filed, and cleaned before I head over to the bender.
I mocked up some steel legs first, taking note of the amount of material pull and the degree of bend necessary for my design. Ti however, is another ball game. Ti has an extrodinary amount of spring back during bending, so the amount of force and angle necessary to achieve the same bend radius as the steel was almost 1.5 times more. Here's a finished Ti piece post bending...
Once bent up, I trimmed a bit of the inside material off the area to be mitered for better fit up, and threw the pieces in the mill...
With the legs cut up, I then turned my attention to the steerer tube, cutting it to length and then turning it true and deburring it for assembly.
One of the disadvantages of being one of the few builders who fabricate Ti forks is that there are not a lot of "off the shelf" pieces, crown races being one of them. For this project, I pulled out my crown race material and after a bit of work in the lathe, have a finished piece...
Boring out the ID for a snug fit on the steerer...
turning down the OD for the press fit of the headset race...
and parting it off...
Wha-La! the finished crown race, ready for welding onto the steerer...
The final push for Jason's fork came Friday evening and I was focused on fabrication, not picture documentation, so you'll see I'm missing a few steps. Everything was loaded into the fork fixture, purged with argon and then welded up...
And a few pics of Jay's completed build, looks quite dandy if I say so...
We finished up at 0230 in the morning and then took turns carving though the moon lit streets of down town, enjoying the cool wind and the startled looks from the local whino's who were surprised with our quick, quiet approach.
Jason had an opportunity to display the bike yesterday at the thrid Groovy Series race, appropriately so as the "bonus race" was a Klunker Classic. Jay finished last, both because he chugged a beer at the start line while everyone else rode off, and because he gingerly carried his bike through the mud so as not to sully it on it's maiden voyage...what a premadona ;)
On a personal note, the last 8 weeks have been very difficult for me, as increased time requirements at the Fire Department have overwhelmed my life, limiting time in the shop and at home to mere hours at a time. The pace I've been pushing has exceeded even my tolerance and as such, you've seen a slow down in shop related postings and email. Christi has been answering email and phone inquiries to the best of her ability so the time I do have can be best used in moving projects forward. It is my anticipation that manpower replacements and promotions will occur soon, so that the demand for personal overtime will diminish and life will return to a sembalance of normalcey for us.
rody
