Saturday, April 24, 2010

Dropouts to Chainstay

Yesterday saw the completion of the first actual joint on the bike I am working on (codenamed Adam Jr.) I attached the dropouts to the chainstays.

Most people "slot" dropouts, but the way I learned it from Doug Fattic was just to plop them on top the the un-slotted stay and fill the gap with brass, then make a fillet above the stay to later file into a nice scallop. I don't see any downsides to this method.

There are upsides, though. For instance, it's incredible easy to "jig," and the jigging is foolproof. First, you take any old axle, space the bolts at the desired width (in my case 130mm, measured with calipers to the nearest 0.1mm), and then make sure they're in line by doing a "four point check" (i.e., treating the dropouts on the axle like the legs of a chair, and making sure all the tabs hit a flat surface together, without wobbling)—and then tightening like mad.

Then you put the bottom bracket in the vise, the chainstays in the bottom bracket, and lay the tabs of the dropouts in the chainstays. You can see this going on (and the gleaming filled-in Ritchey logo) in the photo up top, which is quite beautiful and was taken by Olivier.

That's me working on the more awkward inside face of the dropout, seen through the shop window, and also beautifully captured by Olivier!

And that's what it looked like when I was done. This is the inside of the drive side dropout, where you need extra clearance for the small cog on the cassette. It's pretty easy to offset the dropout with the "Fattic method": you just make sure the dropout tab is all the way to one side in the chainstay before brazing.

Above you can see how the chainstay is offset. You can also see that once I've filed things up, there will be (actually, already is; this photo is a bit deceptive) plenty of clearance for the 13-tooth cog in that freewheel (which is not, alas, the exact one I'll be using—though similar).

It wasn't all great news yesterday! I needed a "mitered top tube" to finish setting up the v-blocks on the Fattic design fixture. This I did, but unfortunately with the properly adjusted v-blocks, I discovered that my top tube miters were a bit off. I actually left my ST angle at 72.67 degrees just in case I screwed up the miter a bit; and since I did, I can now do a 73 degree miter a few milimeters in, and all should be well. I like 73 parallel anyway!

So I'm off to the shop to re-do that miter, file the dropout attachment, and also hopefully braze the seat tube to the bottom bracket. Yikes!

Another postscript: Without realizing what I was doing, I spelt "miter" in the American way in this post. I'll take it as a lesson: stick to your roots. "Miter" it shall be from henceforth, as a reminder of Doug Fattic and Niles, Michigan.

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