Friday, May 21, 2010

Fork Progress

My lack of taps/facers for my bottom bracket combined with my lack of a steer tube to keep me out of the shop for some time. But the arrival of both has resulted in all sorts of action in the last two days.

We got "Xpert" (aka IceToolz—thank heavens they're not sold under that name in Canada) taps/facers. After one tapping and one facing, they seem like a great deal. The kit includes English and Italian taps, and the facer uses a Campagnolo-style spring system. There is some gratiutous carbon tape on the handles, but there's nothing else to complain about. They even come in a nice hard-shell plastic case.

After facing my BB shell I cold set the seat tube into alignment—it was off by a few thousandths of an inch. I can't do much more until yet another tools materializes: a head tube alignment system. Olivier is working on it.

Next, the fork. For a while I've been thinking about the best way of getting a fender attachment point under the fork crown. The nicest I've seen is this one by Peter Weigle, though I couldn't quite figure out he did it (and don't particularly like the way that the steerer isn't brazed all the way in to the crown. I worked out something I could understand a bit better. I took a piece of steel sheet and fillet-brazed it to the bottom (here represented as the top) of the steer tube. Then I filed it flush with the steerer. It ended up looking like this:

Then I drilled a bunch of holes. (Keep in mind that I did all this without a lathe—and actually without even using a ruler. Which is why things are not perfectly aligned.) First I drilled a hole for a water bottle boss and brass-brazed it in place. Then I drilled holes on the "right" and "left," both of which are angled in. These are for passing wires: one for the generator-to-switch wire, and one for the switch-to-headlight. Then I drilled drain holes at the front and the rear. Then I drilled four more small holes, for fun. It came out looking like this:

You'll notice that the water bottle boss is not flush with the bottom of the steer tube like in Peter Weigle's. I left it like this so that there would be room for all the cables to enter/exit the steerer. I left a extra few milimeters in the front wheel clearance to compensate.

The next step was brazing all this in to the fork crown. That went well, though I didn't get all those holes perfectly aligned. It's hard to see when things are covered in flux!

Here is a look at the nice silver penetration (and the gorgeous Pacenti Mitsugi crown, filed into my shape):

And here is everything all is place. I think it looks pretty nice—and of course will be functionally very good too.

I kept my roll going and brazed the dropouts to the fork blades. I did these "slotless," as I did my rear dropouts. With the rake more or less matching my drawing, and with the blades cut to the same length, I stuck everything in Olivier's lovely fork jig. It all seemed to fit together, so I tacked each of the dropouts in two places. (Note the presence of an Arizona iced tea in this moody photo. I accomplish nothing in this world without one by my side.)

Then I took everything out of the jig, put the steerer in a tube block, the dropouts in an axle spaced at 100mm, and fitted it all together.

Using this slotless method has advantages and disadvantages. On the upside, everything is "literal": you don't need to slot the dropouts at any particular slight angle, or really worry about fixturing at all: you just hold it in a fake axle and everything ends up at the right angle. On the downside: there's a lot of cleanup work (filing), and with eyelets things are tricky. I was also a bit worried that it would come out really crooked.

Thankfully it didn't. Here's the wheel held provisionally in place, more or less centred:

I still need to file the dropouts, shorten the blades by a centimetre, and braze them to the crown. But this is more or less what it will look like—though will have a bit less clearance, and a lot less steer tube. The rake on the blades is really nice—thanks to John Clay.

I'll get the fork finished up and hopefully tack and braze the front triangle next week.


James Black said...

Nice work! That's a great fork.

AH said...

Thanks! Now hopefully the whole thing comes out perfectly straight...!

RMHampel said...

The fork looks great, Adam.
I was wondering if tapping in, then brazing something like a star fangled nut into the bottom of the steerer would be an easier way to attach a fender mounting point.