Monday, June 24, 2013

Milestone


This weekend saw a milestone in build #0, that being the first time the main triangle had been fitted together.  Since the dimensions I knew were that the top and seat tubes were 585mm center to center, these were the ones I laid out first on my plywood template.  Once these were cut to length and fitted, the fixed angle of the bottom bracket between the seat tube and down tube revealed the length to cut the down tube at the head tube junction.

Main triangle tubes fitted together for the first time.
Each lug required grinding down the inside surface where it mates with the appropriate tube.  Early on, my reluctance to remove too much material led me to follow a procedure that was like, grind, test, grind, test, grind, test, before finally arriving at a good fit.  By the last lug, this was more grind, grind, grind, test, grind, ok.  It feels good to be learning and getting the hang of it.

I cut each of the copes using a tube angle jig that worked with a 1/2" drill motor and a hole saw arbor that a buddy loaned me.  I cut the correct end of each tube, indicated by a bit of paint at the end to cut, as the thicker butted section is longer at one end than the other.  This is especially important on the seat tube, as it's only butted at the bottom bracket end and requires no cutting to fit into the seat lug.


Drill motor and downtube in angle cutting jig. 

Once the tubes were able to be fit through the lugs, I marked each tube's cutline with a Sharpie and scribe by laying the tubes on the template and setting each tube on its centerline.  These marks can be seen on the sides of the tube in the picture below.  I also scratched a small file mark at the point of each lug so that the tubes could be placed into the cutting jig horizontally, as once one end is coped, the tube's orientation is established.

Preparing to cut the 60 degree cope in the downtube where it meets the headtube.

Finally, once each tube was cut, I fit it into the lug and ground the end flush with the lug.  The remaining tasks to complete prior to brazing the front triangle together are to cut the head tube to length and figure out how I'm going to hold it together and in alignment whilst brazing.

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