UBI Framebuilding Class - Day 7

5/19/2015 - Day 7

• 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

On to Day 8