20130415

YFBS: Day 7 - You Mad Bro?

I'm continuing to document my adventures here at the Yamaguchi Frame Building School.  The first entry can be found here.  

The title of today's entry comes from the phrase of today, brought to you by Matt's reaction to me asking why everyone was hanging out under awnings wearing flannel and smoking cigarettes.  

After a day of rest, we dove right back in to where we left off, starting with silver brazing the clamps onto the stems.  It was pretty exciting coming into class and seeing our stems all cleaned off and shiny, but the clamps still had to be brazed and the finishing done.  I placed each clamp at a time to make sure they were center and level, and then brazed them on.  More pressing matters were at hand, so the stems were set aside for the time being.


My stem sitting with the rest of tubes.  One happy family.
Clamps brazed on - now it really looks like a stem!
Our main triangles needed to be finished, and since this is crunch week the sooner they get done, the better.  Mr. Yamaguchi set up the alignment table with my frame angles, and I proceeded to make the last two miter cuts I needed for the frame.  The first cut was the downtube to the headtube, which has to fit nicely and also line up centerline to centerline.  At this point, the fit must be checked after just a couple seconds of filing each time, so that the angles are still accurate and not too much material is taken off.  Once that miter was done, I mitered off a small arc where the downtube meets the bottom bracket so that the tubes will lock together.  It was almost time to tack!


My tubes all set up, and fluxed.
I sanded, drilled, and prepped all of the tubes while Mr. Yamaguchi showed me how to set everything in the jig.  Liberally applying flux before setting the tubes (bronze for the seat and bottom bracket and silver for the headtube, I got everything locked in place, something that the lugs helped with quite a bit.  Once I dried the flux, tacking began.  


Close up of the head tube in the tacking jig.
I managed to do most of the tacking without burning the tubes, so I only had to do minimal clean up before moving on to internal brazing.  Even minimal clean up is a lot of work though - all discolored areas have to be filed, sanded, re cleaned with acetone, and then covered in more flux before brazing continues.


Close up of the bottom bracket.  The seat and down tubes are cut so that they lock together.
Internal brazing the seat and downtubes was much easier this time, and my frame whistled happily as I moved the torch to pull the bronze inside.  The miter lines were still pretty visible when I was done, meaning I'm sort of getting the hang of internal brazing.  After internal was external, but only for the seat tube.  Since I had to wait for the main triangle to cool down before I could clean it, I started to file down the extra material from the steer tube near the fork crown.


Ready to do some real brazing, and it's looking like a bike!!

Filing takes a long time, especially when you have to be precise.  My fork crown  still had a ways to go in this photo.
My fork was filed and the frame cool to the touch, so I cleaned everything up (sensing a pattern here) and started to externally braze the seat tube.  It was the same process as the stem, except maneuvering the frame around to keep everything at the correct angle was a bit of an acrobatic process, especially since you can't touch the tubes at all due to the heat.  Or, you can, but then you end up with dropouts burned into your face for the next two years, as Mr. Yamaguchi told us.  


The seat tube prior to external brazing.  It might seem like not a lot of bronze was used, but it was all just pulled into the inner seam, reinforcing the frame from the inside.  The More You Know.
After tacking.  Look!  Lugs!
We're not external brazing the bottom bracket until the chainstays are tacked.  
The last task for the day was silver brazing the lugs.  Since the little parts of the lugs heat up really, really quickly, this was much harder for me than the fork crown was, and I ended up burning more areas than I would have liked to while pulling the silver through the lugs.  Near the end I was doing much better, but there's still going to be a lot of clean up.


After silver brazing.  The black is bad, but the green is good.  Temperature is really, really finicky when silver brazing, and great care has to be taken to not burn the tubes.  It's something that comes with experience, Mr. Yamaguchi told us. 
And with that, my main triangle was done!  Tomorrow I'll begin the seat and chainstays.  I almost have a frame.  


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