SF Cyclotouring

Ride reports and other ramblings from a San Francisco cyclist.

6/14/2015

UBI Framebuilding Class - Day 7

5/19/2015 - Day 7

UBI

UBI

UBI

UBI

UBI

UBI

UBI
  • Seat Stays
    • Attachment Styles:
      • Traditional
      • Fastback
    • Choosing Seatstays
      • Typical diameters: 14/16/19mm
      • Consider proportions to main frame -- fat tubes with skinny seatstays will look odd, etc.
      • Plug/socket-style dropouts will dictate the SS diameter
      • You will need to cut a tab on your dropout
      • Also need to cut a slot in the SS for the dropout tab
      • Double-tapered SS are useful for canti brakes
      • You can bend your own SS -- use the fork-blade bender
      • Canti brakes -- be aware of SS width vs. canti-boss placement requirements (75-85mm boss spread)
    • SS overview drawing
      • Measure axle to SS contact point
      • Center of axle to end of dropout tab
      • Lay seatstay on drawing, gauge tire clearance
      • For Canti-studs
        • Measure up to the BSD line
        • Boss spread is 75-85mm
        • Draw horizontal line at BSD to estimate boss locations
    • Fitting Seatstays
      • Cut & Slot for Tabbed Dropouts (same technique as CS and fork blades)
      • Bevel inside of drive-side stay more and steeper for cassette/chain clearance
      • Drill vent holes (1/16-inch bit)
    • Brazing Seatstays
      • Always use dummy axle
      • Fixture SSs using spring-thing clamp, leather toestrap, or similar
      • Braze using silver filler at seat lug, brass filler at dropouts -- remember to use the correct flux for each!
      • Braze in a bicycle work stand, not the frame jig, for better access
      • Tack inside points of dropout tab/notch lightly, to avoid lifting the seat stays off of the seat tube
      • Heat edge of dropout tab until red, then "walk" the heat up towards the notch/slot
      • Heat the seat lug, watch for the lug's silver to melt
      • Tack at the tops of SS
    • Seatstay Attachment w/Custom Caps
      • Choosing the material
        • Use flat stock or large-diamter tubing (e.g. fork blade cutoffs)
      • Mitering
        • Choose an angle -- shallower (longer cap) is harder to fit
        • Use bevel gauge to match desired angle of tube clamped in block in bench vise
        • File parallel to floor with half-round or flat file -- depending on the cap material (round or flat)
        • Make stays the same length
        • Minor length adjustments can be made at the opposite slotted end for the dropouts
      • Brazing the Caps
        • Slide cap to just the bottom end of the oval cut into the seat stay
        • Tack bottom with brass
        • Tack at top end
        • Tin brass around -- watching for gaps and pinholes
      • Finishing
        • Remove excess material with any available method (bench grinder, hacksaw, snips)
        • Clamp stay parallel to floor
        • Only file flat
        • Rotate stay, not file
        • Finish file until there's a single shiny line
        • Leave top point 4-5mm long for finish fitting (can do slight wrap-around effect on seat lug)
        • Caution: Do NOT file into the stay
        • Pick desired top point, mark with Sharpie
        • File to point, leaving 4-5mm long
        • Clean off burnt flux, because silver won't stick
        • Use emery cloth on end of seatstay to finish and smooth
      • Fitting to Frame
        • File a groove with a round file in seatstay lug pointing in direction of seatstay dropout tab
        • Locate groove by inking seat lug with Sharpie and scribing seat stay along lug to mark the seat lug
        • Choose desired landing point for seatstay -- into the lug's "valley" is typical
        • File GENTLY; watch that scratch marks from file are centerd over scribed marks
        • STOP if you hit silver, do NOT go deeper

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