SF Cyclotouring

Ride reports and other ramblings from a San Francisco cyclist.


UBI Framebuilding Class - Day 5

5/15/2015 - Day 5

UBI: picking frame tubes





  • Frame Tubing
    • Choosing Frame Tubes
      • 8/5/8 is OK to use
      • Wall thickness
      • Overall length of tube should reach to at least halfway across adjacent tubes
    • Check seat tube with actual seat post to ensure fit and determine butted/non-butted ends
    • Locate tube butting (look inside)
      • Watch for short vs. long butts
      • Bias long tube butts towards the headtube
    • Mark tubes just past center of adjacent tube
    • Label tubes and their orientation
  • Machining Dimensions (see worksheet)
    • TT/ST: 73°/17°
    • TT Miter Length: inside corner to inside corner
    • TT/HT: 73°/17°
    • Notch ST for Lugged BB, Notch DT for Fillet-brazed BB
  • Tube Mitering 
    • On the Milling Machine
      • Diameter of Cutting Tool/384 = approximate cutting RPM
    • By Hand (specific to TT/HT Joint, others similar)
      • Only rough-cut one end
      • Scribe to inside of headlug
      • Use Bevel Protractor/angle gauge set to HT/TT angle as filing guide
      • Cut miter and file
      • Clean out inside of tube (file/emery cloth)
    • Scribe mark down length of HT for vent hole locations
    • Drill 0.25-inch hole (#3 drill bit)
  • Henry James Jig Set-up (specific to HT/TT)
    • Level out the TT blocks against the jig's backplate with provided angle-iron
    • Set centerlines for TT
      • Adjust lower blocks first
      • Adjust upper V-blocks next
    • Set Head Angle -- watch for loose gauge block
    • Head Tube Rod - put HT on
    • Head Tube Height Adjustment
      • Align HT vent hole with TT
      • Check HT height from drawing
    • Rock tubes in lug to ensure they're fully seated
    • Make sure all clamp bolts are tight
  • HT/TT Brazing
    • Silver flux everything
    • Rotate jig to expose obtuse angle of tubing/lug joint
    • Tack obtuse angle
    • Tack acute angle
    • Follow brazing sequence to complete lug braze
    • "Paint" with torch flame to move the silver where you want it to go
  • Seat Tube
    • Notched for lugged frames to locate tube in BB
    • Locate ST in BB and lay on drawing to locate ST/TT vent hole
    • Check BB port angle against drawing
  • Brazing the Frame
    • Mount tubes in Henry James jig
      • Ask instructor for help
      • Flux everything
    • Brazing
      • Remember: Obtuse angles first
      • Tip jig to point joint downwards to leverage gravity
      • Use soft reducing flame, barely roaring
      • Start w/HT/DT lug, braze similar to HT/TT lug 
      • Move to BB (rotate jig)
        • Do obtuse/bottom/outside angle first
        • Then do back/acute angle
        • Don't cook CS ports
        • FEed fillter at DT, look for it at ST
        • Then do sides of ST
      • Last do ST/TT lug, obtuse angle first (rotate jig)
        • Feed filler at TT, look for it to come out at ST


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