Building the Frame's Main Triangle

After the seat tube was brazed into the bottom bracket, and the down tube lightly tacked in there too, we began brazing together the rest of the front triangle.

I should mention that the tubes are all perfectly mitered at this point, and all the lugs have been reamed and gone over with a Swiss file. The lug points are pointy and there are no little bits of flashing that might get in the way.

There is a sequence for proper brazing, and it goes:
1. Down tube to head tube
2. Top tube to head tube
3. Down tube to bottom bracket
4. Seat tube to top tube

Between each braze we checked alignment with the surface gauge. Most of the serious brazes are done with the tubes clamped into the vise, not in the jig, because it's easier to move things around in the vise and the extra flux can drip onto the floor instead of on the expensive metal jig or smooth work table.

After mitering, the tubes fit perfectly together. We can set all the tubes up in the jig and they should all fit like this. If not, then we get out the files and make small adjustment. Doug used a sandblaster to clean all the tubes, but afterwards we also went at the ends with sandpaper to make certain the connection is clean.  

This exhaust hole is drilled into the head tube where it meets the top tube so that gasses have a way to escape while brazing. 

Here is my frame, ready to be tacked so that the tubes don't move around during the final brazing. 

Here's my classmate showing good brazing form while tacking his tubes in place. That's Doug keeping an eye on things.  

Any time heat is applied to the frame, alignment must be checked. We use the tubes right next to the BB as the base measurement, and try to get all the other tubes as close to that as possible. This is one of the most time-consuming parts of frame building. Quality takes time. My frame is within 1mm of alignment at every angle. Also, see how we leave a little extra head tube sticking out of the front lugs? That's so that the braze has something to leak onto, but is also useful for checking alignment. 

Here's the front, covered with flux, ready for brazing

Here's what the braze looks like immediately after applying heat. This is my custom lug, and you can see the flux is still dripping. I'll wash that off with warm water. 

Here I am thinning my lugs out and polishing with my Swiss file. 

The frame gets a nice rusty patina after we washed off all the flux with warm water. The rust will be sandblasted away by Doug before we do anything else. 

At the end of the day, Doug and I rolled down the Niles Branch of the River Valley Trial to the park next to the river to see the weekly car festival. The people of Michigan love cars, so it was a good show; lots of makes, models, years and styles. Here is an beautiful example of one of my favorite cars, the 1987 Nissan 300ZX, with a turbo charger, manual transmission, and t-tops. I had one of these in high school, but this one is much, much nicer.