Mitres

To all appearances, the mitres for my bike are now complete. I brought the camera in to the shop today, and here is what I did.

To make sure that the top tube mitres were indeed right, I needed to have all the tubes in place. This meant mitring the down tube at the bottom bracket, to let the seat tube in. I did this by inserting the ST into the BB and tracing lines with a Sharpie. (This also gives you a much better look at the carving I did for the BB.)

With the lines drawn on, the tube—whose "REYNOLDS 531" marking you can see if you squint—now looked like this:

First I took my biggest file, which produces a round shape with a 1 3/8" radius, equal to the inside of the BB shell. This left things looking like this:

That last outline corresponds to the place where the down tube meets the seat tube in the BB shell. I filed that out (with a smaller file whose shape corresponded to 28.6mm), and then stuck the tube in the BB shell to check if things fit. And they did, though I did very slightly mess up the back of the DT/BB joint. About a milimeter too much material taken off, so I won't worry. The fit was thus:

And thus:

Then I returned to the fixture to try to stick all the tubes in place. The ST and HT still interfere a bit in the BB, but I'll take care of this once the ST is brazed to the BB. Here's how things look:

With all the tubes in place, everything mercifully fit together. Here's a poor photo of the fixture with all the tubes in place. (I had to hang off the wall even to get this bad shot; I need a wide-angle lens!)

The down tube/head tube mitre:

The top tube/head tube mitre:

And the seat lug, holding things in place. (I am very sure that, beneath this lug, the mitre is where it ought to be!)

Since I was on a mitring roll, I decided to try mitring the chainring bolt I intend to use as a braze-on to mount a taillight on the seat tube. Its diameter is 10mm, the tube is 28.6, and the angle 62.67. I pushed my mitring system to the logical limit and printed off a TubeNotcher+ mitre.

It was extremely hard to hold the little guy in the vise securely enough to get a good grip, but eventually the mitre was more or less made. Olivier's little clamps seem like they'll work to keep it in place for tacking. I'll need to file off that chrome plating first, though...

The next step: brazing the seat tube to the bottom bracket!

Postscript: Reader johnb very helpfully pointed out that I was using the American spelling, "miter," in the first version of this post. No doubt this is because I learned to build bikes in Niles, Michigan. In deference to my generally European leanings—and with no disrespect whatsoever to Niles or to Michigan—I have altered this.

His comment led me to look up the origin of the word "mitre"/"miter." The main sense of the noun in the Oxford English Dictionary refers to a hat, specifically the ornate headdress of a bishop. The second sense, "A usually right-angled joint in wood or other material in which the angle made by the joined pieces is bisected by the line or plane of junction," apparently derives from the first. According to the editors of the OED, "the early form of the episcopal mitre [...] had a vertical band bisecting the angle at the top." I shall keep the bishop's hat in mind the next time I miter—nay, mitre!—a joint.