UBI Framebuilding Class - Day 3

5/13/2015 - Day 3

• Third Lug Practice
• About Bike Frame Tubing
• 9/6/9 Butted wall thicknesses
• Butting lengths
• Can see butt transitions inside a clean tube
• Butted lengths vary widely, and can be asymmetric (one butted end is longer for trimming)
• Seat Tubes
• 28.6mm is most common, to fit a 27.2mm seat post
• Single butted for lugged construction
• Single-butted at bottom and EXTERNALLY butted at top for fillet-brazed construction
• Choosing Frame Tubing Diameters
• 1 inch steerer dictates 31.8mm head tube; be sure to choose an appropriate lug
• 8/5/8 tubing is light
• 9/6/9 is mid-range
• 1/7/1 is heavy
• Tubing choice factors
• Rider weight
• Rider strength
• Cargo load
• Frame size (larger frame implies stronger tubes)
• Pick lugs first, since these might limit your tubing options
• Frame Drawing
• Work clockwise
• Use a SHARP pencil for accuracy
• Choosing the lower head lug is an iterative process due to unknown HT/DT angle
• Drawing steps (refer to workbook)
• Draw axle line about 7cm from bottom of paper
• Draw BB drop
• Draw seat tube centerline at correct angle from BB point and to desired length
• Draw TT centerline to desired length
• Draw HA/HT centerline back to axle line
• Draw Fork Offset parallel to HT centerline
• Draw arc set to radius appropriate to desired tire Bead Seat Diameter around front wheel axle center
• Choose a fork crown
• Consider caliper brake reach (if using caliper brakes)
• Draw in perpendicular line for 13mm lower HS stack height
• Measure lower head lug intercept
• Draw in headtube width (31.8mm)
• Add intercept distance
• BB shell
• For lugged, use the ID of the shell (typically 35mm)
• For fillet, use the OD of the shell (measure shell)
• Forks
• Dropout styles
• Tab style vs. socket style
• Socket style has more limitations for fork blades due to requirement for matching diameters
• Blade lengths
• Blade thickness
• Raking fork blades 
• Check blade length before bending
• Iterate/sneak up on desired rake, alternating between both blades
• Get both blades as even as possible
• Cutting fork blade dropout slots
• 6-8mm depth is good rule
• Clamp using wooden blocks
• Sight down the bend/ridge of the blade to align the dropout slot
• Make a Sharpie mark
• Scribe width of dropout on blade parallel to sharpie mark, and centered with it
• Scribe slot depth onto blade
• Clamp and cut
• Bias the slots inboard for extra hub clearance
• Rotate the blade 90° and angle it to about 30° with floor
• Use a large flat file to knock down the corners and bevel the edge
• Use bevel protractor to gauge bevel against clamping blocks for repeatability with other fork blade
• Clean out burrs with round file

On to Day 4