Originally Posted by
scarlson
First of all, I am without a scratch.
My Trek came with the slightly infamous Ishiwata death fork, which I was told not to worry about but maybe keep an eye on. It looks like I did not keep good enough eye.
Cracked on both sides. Looking at the cracks, there's some rust in there on the crack surfaces, so it's probably been there all along. That's good - it means it's not my fault for brazing cantilevers onto it or whatever! I mean, hek, it's nowhere near anything I brazed.
I've put some hard miles on this Trek in the past year since I built it. One thing kept rearing its ugly head, however: violent brake judder! It almost seemed like the brakes had a servo effect, like the fork was flexing enough on braking to cause the brakes to be applied all the more. I changed pads, which made it go away for a little while, but then it came back, worse than before! Another 200 or 300 miles after that, I was riding on a damn sidewalk after a bbq with friends, and testing out the brakes (just for fun, y'know, at low speeds, to try and figure out the judder), and it did a surprise front-wheelie. I thought it was the beer! I put the rear wheel back down, kept riding, but the bike felt funny. This crack is what I found.
@
gugie , got any tips on building my first fork? I'm thinking to make it wide, for 48s, because 48s are the new 42s.
That'll buff out.
Building a fork is just like building a frame, but is very different. ;-)
I just built a fork for my Ritchey Breakaway to replace the early 80's looking ultra-beefy mountain bike fork that it came with, then a few weeks later had @
SquireBlack over for his first fork building session using the method I learned at UBI 5 years ago. You need to figure out two parameters you want, A-C dimension and trail - which as you know is a derived dimension using head angle, fork offset, wheel diameter and tire size. Framebuilder Supply has a good selection of wide fork crowns. I like the Pacenti MTB fork crown for super wide tires, I used that on my gravel bike build with RTPs on it. They also sells pre-bent fork blades that are fairly good. That relieves you of the need for another jig as well. Since you're not using disc brakes those blades should work just fine.
As for tips, you'll need a fork jig. With your machining abilities (and assuming your access to the school shop is back in business), I'm sure you can make your own out of unobtanium castoffs.
Order of assembly as I learned it:
1. Steerer to fork crown, steerer inserted just proud of the crown. Pin the fork crown to the steerer, hold it upside down, apply filler to the steerer-crown at the "proud" section, use heat to draw it down until you see it coming out at the crown race end.
2. Trim blades at the tapered and curved end for the offset you want.
3. Prep the ends for tab, lug, or plug style
4. Braze dropouts in. You can do this either with a special jig, or just use the fork brazing jig with the blades dry fit into the fork crown. I just use the fork jig i have - the key here is to get the alignment of the dropouts to the blades as good as possible to minimize cold setting them later.
5. Your blades should be too long at this point. Trim the fat end of them a couple of mm's long to achieve the A-C dimension you desire. File them perfectly square to the straight portion of the blades. I use a very small square to check front to back and side to side squareness.
6. With the blades dry fit into the fork crown, insert a test wheel. If it's not centered perfectly, file one side down a bit and retest. Recheck your A-C measurement. If you're within a mm, I'd say you're good to go.
7. Jig up the assembly, braze in the blades upside down.
8. Use H-bars to align dropouts perfectly.
Don't braze on the small bits until the fork is done.
I skipped a ton of small things, but already got the knowledge and chops to figure them out. If not, you've got my email address.
Or, wait until Doug Fattic, Mark Bulgier, or John Thompson chime in and give you the correct way.
