8 Steps, ~3 hours
Goal: In this section, you’ll begin to make your frame. You’ll end it with a frame tacked in your jig. The temptation in this section is to work quickly… however, precision and care in this stage will make a big difference as you move through the rest of the process. Also, you’ll want to move on to the next section within 48 hours. Once the bamboo is roughed, the lignin is exposed. Allowed to sit too long, the exposed lignin can dry quickly and induce a split. This section takes roughly 3 hours to accomplish.
Materials: • Bamboo • JB Kwik (Black and Orange tubes) • JB Weld (Red and Black tubes) • Mixing Stick • Gloves • Pull Saw • Sharpie • Measuring Device • Front Seat Lug • Rear Seat Lug • Balsa Shims • Wheel Clearance Checker • Painters Tape • Paper Towel • Denatured Alcohol
****NOTE: The video says to use the blue JB Kwik tube. JB has switched the colors they use so please use the JB Black we provided instead****
4.1 Prep & Install | Cut & Rough Seat Tube
4.2 Prep & Install | Tack Seat Tube
• We want to be careful in our handling of the the metal Seat Tube Sleeve. Oils from the hand can cause weak bonding. If you do touch the Seat Tube Sleeve with a bare hand, be sure to wipe it down with some denatured alcohol prior to bonding.
• Put on rubber gloves.
• Using a 1:1 ratio of JB Weld Epoxy to Hardener, squeeze two quarters’ worth from the red tube and two quarters’ worth from the black tube onto a piece of cardboard. JB Weld is ostensibly non-toxic, but it is very difficult to remove from fingers once it dries.
• Mix with the mixing stick until uniform color.
• Starting 2 cm below the notch on the Seat Tube Sleeve, cover the Seat Tube Sleeve evenly in a thick coat of JB Weld. This should be like putting a thick coat of peanut butter on a sandwich. The coating should be thick and even.
• Work the epoxy back and forth, into the Seat Tube Sleeve grooves.
• Place the Seat Tube over the Seat Tube Sleeve. The JB Weld should fill the gap between the Seat Tube and Seat Tube Sleeve.
• Rotate the Seat Tube Sleeve and work it in and out of the Seat Tube. This works the JB Weld into the rough inner surface of the bamboo and into the etching on the Seat Tube Sleeve.
• Leave at least 1cm of etched Seat Tube Sleeve above the top of the bamboo.
• With your mixing stick apply some mixed JB Weld to the bottom of the Seat Tube, where it touches the Bottom Lug. Try to center the Seat Tube on the Lug face. Hold in place for ten seconds.
4.3 Prep & Install | Glue Seat Tube Lugs
• Place the Top Lug on the front of the Seat Tube, so that the top of the Top Lug lines up with the top of the Seat Tube.
• The inner surface of the Top Lug will probably not match the outer diameter of the bamboo.
• File, holding the file parallel to the inner surface of the lug and using slightly circular motions.
• Be careful not to take too much material away. Take small amounts and check the fit, repeating if needed.
• Test the fit of the Lug and the Seat Tube again.
• Continue until you get a snug fit.
• Repeat with Seat Lug, placing it on the back of the Seat Tube, so that the top of the Seat Lug lines up with the top of the Seat Tube.
• Using a 1:1 ratio of JB Kwik Epoxy to Hardener, squeeze two quarters’ worth from the orange tube and two quarters’ worth from the black tube onto a piece of cardboard.
• Mix with the mixing stick until uniform color. Once mixed, you have 4 minutes to work with JB Kwik before it hardens.
• Apply a thick smear of the mixed JB Kwik to the inside of the Front Seat Lug.
• Attach the Front Seat Lug to the Seat Tube, so that the top of the Front Seat Lug lines up with the top of the Seat Tube.
• Ensure the sides of the Foam Lugs are parallel with the MDF board and centered on the bamboo Seat Tube.
• Press the Front Seat Lug around the Seat Tube and wait 10-15 minutes while the epoxy hardens.
• Apply a thick smear of the mixed JB Kwik to the inside of the Rear Seat Lug.
• Attach the Rear Seat Lug to the Seat Tube, so that the top of the Rear Seat Lug lines up with the top of the Seat Tube.
• Press the Rear Seat Lug around the Seat Tube and wait 10-15 minutes while the epoxy hardens.
4.4 Prep & Install | Cut & Rough Front Triangle
• When selecting your Down Tube and Top Tube, use the larger of your pieces for the Down Tube.
• Inspect your bamboo for possible splits, or stress concentrators
• As you fit the bamboo, be sure to point the nodes towards the ground plane.
• If there are any gaps between the bamboo tubes and Lugs, wedge a balsa shim into the space. You’ll file down the shims in a later step.
4.5 Prep & Install | Fit, Cut, & Rough Stays
4.6 Prep & Install | Add Tire Clearance Check Tool
4.7 Prep & Install | Tack Front Triangle
4.8 Prep & Install | Tack Stays