UBI Framebuilding Class - Day 4

5/14/2015 - Day 4

• Measuring Fork Crown Blade Seat
• Check catalog specs OR use the back side of the caliper to measure the blade socket depth
• Measure each side in case they're different
• Mark line across outside of fork crown
• Measure to crown race seat
• Mark on your drawing -- line perpendicular to HT between fork crown race seat and underside of fork crown/tire clearance
• Draw 11/32-inch circle on frame drawing at front axle center
• Fork Dropout Jig
• Ensure symmetry in slot at dropout dummy axle
• Position blades & dropouts in jig
• May need to refile slots to adjust blade angle to get ovals parallel
• Measure inside width of fork crown sockets (95.6mm)
• Flip calipers over & measure outside width of fork blades at crown height
• Check slot fit
• Check blade ovals for parallel
• Brazing fork dropouts
• Use 2-4 inches of brass rod per dropout
• Tack corner points first
• Seal tab sides
• Then fill plug
• Braze one dropout, then the other
• Chainstays
• Overview drawing (see worksheet)
• Dropouts
• Tire Clearance
• Figure out seatstay angle to help select dropouts (70°)
• Chainstay length
• Axle spacing
• BB Shell width: 68mm
• BB Shell diameter: 35mm for lugged
• Axle to back of BB length (should equal CS length minus (35mm/2))
• Draw overview on frame drawing
• Choosing BB shell
• Round vs. Oval chainstays
• Seattube & downtube diameters
• Tire clearance
• BB edge to chainstays
• Chainstay to dropout angle
• Draw OLD of hub axle
• Add 1/2 thickness of dropout -- watch for thick/raised dropout faces
• Measure dropout tab length -- axle center to end of tab
• Draw tab on drawing
• Mark tab depth (6-8mm)
• Mark slot depth (6-8mm)
• Determine overall chainstay length
• Draw in tire diameter
• Choosing Chainstays
• Straight vs. S-Bend
• Round vs. Round-Oval-Round
• Draw Line along Chainstay
• Measure Chainstay Angle with Protractor
• Chainstay Fixture
• Dummy Axle
• 137mm for 135mm OLD rear
• 132mm for 130mm OLD rear
• 122mm for 120mm OLD rear
• 102mm for 100mm OLD front
• Dummy axle slop -- keep in phase
• Mark chainstay length for back of BB off of frame drawing
• Check BB shell CS socket width with calipers
• Mount stays & drops in chainstay fixture -- watch for any gaps at tabs
• Adjust CS clamp fore/aft to set proper CS width at BB sockets
• Fork Blades
• Mark each fork blade length off drawing -- add 1mm to length
• Cut to line -- ensure cut is perpendicular to blade
• Clean up cut with flat file and level
• Deburr inside and outside of cut blade
• Check for square cut with machinist's square
• Fork Crown
• Mark left & right on crown for orientation and keep this orientation for fork leg insertion
• Clamp blades in dummy wheel
• Check alignment
• Tweak as needed
• Sight down through empty steerer hole in crown to check for center
• Side with more rim clearance is the shorter side -- LIGHTLY file down other side 
• Iterate to get alignment perfect
• Squish oval ends of blades in vice as needed to fit crown
• Fork Vent Holes
• 1-2 inches above dropout; 1/16 inch hole only
• 1-2 inches below fork crown; 1/16 inch hole only
• Deburr any holes
• When drilling, clamp dropouts, not fork blade
• Brazing Fork Crown
• Anvil Fork Jig
• NOTE different offset scales for 1-inch and 1-1/8-inch steerer tubes
• Sand & wipe down with alcohol
• Check for close fit at fork crown tangs & points
• Add Silver flux everywhere -- inside and outside of crown; use LOTS of flux
• Fork blades should evenly touch alignment bar on jig
• Use a hotter/bigger flame
• Braze fork in jig upside down
• Heat steerer tube first
• Start at fork crown front and work around
• Heat from top to bottom
• Load silver on top (underside of crown) and pull it to bottom of crown (top side of crown)

On to Day 5