9th class-

Homework was to get the flux off the newly brazed parts of the main triangle.

The day was spent on 2 things- setting the frame jig up to braze the chainstays and getting the chainstays to fit into the bottom bracket socket.


So here is one of those times when you appreciate something you not only took for granted, but actually never even thought about.
I have never thought twice about the shape of a chainstay(or really any other tube) insofar as to the difficulty of building a bike. Round chainstay means a bottom bracket shell with round sockets to accept the stay’s shape. Ovalized chainstay means a bottom bracket with oval sockets, etc etc etc.
Well I learned that not all ovals are the same! What Columbus thinks is an oval is SIGNIFICANTLY different than what Henry James(lug and tubing supplier) thinks is an oval. When I say its significant, its really quite small…like less than 1mm different…but that is HUGE in terms of fit.
The Columbus tube were way too big for the shell’s socket holes and also slightly different in shape.

This oval is different from what Columbus thinks is an oval.

First we slightly bent the stays so they are even more ovalized to give the stays a better chance of fitting. Then I spent a couple hours working on widening(reaming out) the bottom bracket shell’s sockets. I used a pneumatic grinder. I used multiple files. I used sandpaper on a drillbit.
The stays would go in with a lot of pressure, but they should slide in and out with slight resistance only. Basically they need to sit in place, but remove easily.
My well used Sharpie came in handy by making the shell black and fitting the stays in. Then anywhere the black was gone showed spots which needed to be ground down. Its was this process over and over again.

Sandpaper on a drill. This is after using a grinding bit on the drill.
Closeup of the stay sockets. You can see the high and low spots(shading by Sharpie)

During the process of widening the sockets, I also fit the chainstays to the correct length and mitered them to the curvature of the shell. That Sharpe came in handly once again. Fit the stay in the shell to the correct distance, color the part of the stay that is too far in the shell, then cut the stay accordingly. Metal cutters start the angle, a belt sander helped take a bunch of material away quickly, and files finish the job.
In the vice to determine how much chainstay to cut off inside the shell

We then set the frame jig up to get the correct angles for the chainstays. The bottom bracket drop was set and the stays were dryfitted. I hand-bent(toss it in a vice) the dropouts to fit flush against the 130mm dropout tool.

This is where I left things for the day. Before leaving, I asked when we would add the internally routed brake cable. Well that got awkward because it should have been done before we brazed the top tube to the lugs! It was a design element I mentioned before starting the class and not since, and didn’t think it needed to be done until we worked on all the brazeons(bottle bosses, brake bridge, etc). Oops. So we will still do the internal routing, it just wont be as easy to set the brass tube inside the frame that holds the cable. I said I am patient and determined on getting the routing set up, so it isnt an issue.
We arent doing the internal routing with full cable housing like I have on my Miyata 912 and what is on Ironman bikes. Also, the holes will be at about 8oclock which is nice for keeping out water, instead on the top of the frame like my 912 has.