SF Cyclotouring

Ride reports and other ramblings from a San Francisco cyclist.


UBI Framebuilding Class - Day 6

5/18/2015 - Day 6



  • After Brazing Main Triangle
    • Examine the frame for any imperfections or needed touch-up -- mark these with Sharpie
    • Inspect inside BB for silver penetration
    • Too much silver needs to be removed by filing out with an appropriately-sized half-round file
  • Chainstay Mitering
    • Rough-cut to ~15mm extra at BB end to allow for miter
    • CAUTION: do NOT rough cut chain stays to the back-of-BB length!
    • Get 132mm dummy axle, mount stays onto axle
    • Put subassembly on drawing, mark CS tube length at back of BB shell
    • Record the axle-to-back of BB measurement
    • Set a caliper to the BB socket width
    • CS Mitering done with 35mm hole saw, to match inside ID of BB shell
    • Fillet-brazed bikes often have the chain stays offset lower to the BB to provide some clearance for the ST braze
    • Lugged bikes have the chain stays lined up directly, not offset
    • Miter on milling machine
  • Chainstay Fitting
    • Clean off burs from CS end
    • Clean out BB ports with files and emery cloth
    • Resize oval end of CS to fit BB port (squish in bench vise)
    • Take length above BB (38mm) along seat tube ~500mm
    • Triangulate on frame to determine CS angle/height
    • Scribe line on edge of seat tube
    • Check for free movement to desired position - file BB ports as needed
    • Fillet-brazed frames need vent holes in chainstays & BB shell
  • Chainstay Brazing
    • Set up in jig
      • Leave CS shy of inside BB port by 1mm to allow a ledge for silver filter to collect (otherwise it runs inside onto BB threads)
      • Mark outside of chaintsays
      • Set jig to correct BB drop
      • Tighten center bolt of CS boom on jig first
      • Check inside BB with flashlight to ensure proper CS position (leaving 1mm ledge)
      • Check CS socket points on BB shell, use punches to tighten up ports as needed
    • Brazing
      • Flux inside and out, careful of the BB threads
      • Flux halfway around the ST
      • Paint extra flux up the chainstays (which will be pointing UP when brazing)
      • Focus heat on BB since it's thickest
      • Start on non-drive side
      • Heat seam of port on BB
      • Make sure BB stays hot since silver filler needs to flow there
  • Frame Alignment
    • Rear Dropouts
      • Use Calipers to check OLD measurement 
      • Use H-tools for dropout alignment
      • Use long length of flat stock placed under BB and under H-tool to check for even dropout height
      • Use known-good wheel to check for rear triangle alignment
      • Use frame alignment gauge (Park FAG-1 or similar)
      • Check for even spacing at top of rim with long flat stock along main triangle
    • Assess overall alignment picture
    • Make a plan to correct alignment
    • Bend chainstays to correct


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