Step 5: Shape Lugs

Step 4: Prep & Install | Step 6: Fiberglass the Lugs & Carbon-Wrap the Dropouts

5 Steps, ~2.5 hour

Goal: File the Lugs into smooth shapes and transitions that will act as wrapping surfaces.

Materials: • Rounded File • Sandpaper • Dust Mask • Safety Goggles


5.1 Shape Lugs | Shape Head Lug

Why do we make composite lugged bikes?
Why do we use lug cores instead of mitering?
Why do we use balsa wood for lug cores?

• Put on your dust mask and safety goggles. This step creates a lot of fine dust that you don’t want to get in your eyes or breathe in.

• Take the rough side of the rounded file and remove a band of balsa wood on the Top Tube – Head Lug junction. This landing cylinder should be 1 cm wide and stretch around the circumference of the Lug, between the end of the bamboo Top Tube, and the beginning of the Head Lug.
• As you file, err on the side of caution. It is better to leave too much balsa than to file too much away.
• Repeat on the Down Tube – Head Lug junction.

• Using the rounded file, remove some Head Lug balsa, bringing the Lug down to meet the Landing Cylinders.
• File off the corners of the Head Lug, connecting the landing cylinders to the rest of the Lug with a smooth line.
• As you remove balsa, take care not to file away too much–you can always file more later.
• Don’t worry about making the perfect final shape at this point. The form will emerge from itself as it becomes more refined. Create a smooth egg shape, or elliptical cross section.
• Feel for symmetry between the left and right sides of the Head Lug. Adjust any unevenness or bumps.
• File off any excess epoxy from where the Top Tube and Down Tube meet the Head Lug.
• File off any extra material from any shims.


5.2 Shape Lugs | Shape Seat Lug

• Shape the Seat Lug using the same method described above.


5.3 Shape Lugs | Shape Bottom Lug

• Shape the Bottom Lug using the same method described above.


5.4 Shape Lugs | Summary


Bike Making FAQ

Step 4: Prep & Install | Step 6: Fiberglass the Lugs & Carbon-Wrap the Dropouts