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

On to Day 7