Step 9: Carbon-Wrap Lugs

Step 8: Prepare Lugs for Wrapping | Step 10: Finish Lugs

8 Steps, ~1 hour

Goal: Carbon-wrap and compress main Lugs.
Materials: • Gloves • Mini Pump • Epoxy Resin • Epoxy Hardener • Plastic Container • Mixing Stick • Compression Tape • Scissors • Carbon Fiber Spools • Carbon Fiber Patches • Safety Sleeves

Note: Do not stop half-way through wrapping a Lug. Once you start wrapping a Lug, make sure you finish wrapping the Lug and compress it before taking a break.


9.1 Carbon-Wrap Lugs | Introduction & Wet Out Bottom Lug

• This step uses epoxy resin. Make sure you have adequate ventilation: open your windows, and if you have a fan turn it on. Put on your gloves, sleeves, apron and mask. Make sure the temperature in your space stays above 70 F (21 C).
• Put on your gloves, sleeves, apron and mask.
• Push two pumps of clear epoxy and two pumps of red hardener into a plastic cup.
• Mix until uniform color – about 30 seconds of sustained mixing. No streaks!
• This will take 30 minutes to begin to cure. As the resin sets it will get hot. Take care not to burn yourself – once it gets warm, rinse out the resin with water and mix up a new batch.

• From your earlier filing and sanding work, the dried resin should be as smooth as possible.
• There should be no sharp pieces of resin that will act as stress concentrators in the Lug.

• With your gloves on, wet out the entire Bottom Lug, around the Bottom Bracket and up to the roughed areas on the bamboo.


9.2 Assemble Jig | Wrap & Compress Bottom Lug (Spool #1)

• Unravel a five inch section of the carbon fiber and dunk it in the resin. There are 24, 000 strands in the carbon fiber: you’re trying to get every strand wet.
• Run it between your fingers to get rid of the extra resin.

• To start the wrap, lock off around the Bottom Bracket Shell. This wrap will anchor the carbon around the Bottom Bracket. Keep this wrap tight.
• Wrap up around the Seat Tube, lock off around the roughed bamboo. Lockoff points are the softest part of the Lug, so you want to always avoid locking off on the balsa wood, which is already under high stress.
• Now wrap down to the Bottom Bracket, locking off around the Bottom Bracket Shell.

• Remember the Four Laws of Wrapping:
1. Always completely wet the carbon fiber in epoxy.
2. Always lay the carbon wide and flat: avoid it twisting.
3. Always wrap the carbon fiber tight: wrapping it loosely will make your bike weak.
4. Cross the carbon over itself: do not simply spiral it around the bamboo.

• You’ve created a figure eight pattern. Repeat this pattern five times on this side.
• Remember to slightly offset the pattern to maximize coverage, and vary the positioning of your lock off points.
• Now repeat this figure eight pattern five times on the other side of the Bottom Lug.
• Keep dipping your fingers into the epoxy and rubbing it on the balsa Lug. This will help make sure you’re wrapping wet.
• Once you’ve completed this pattern five times on each side of the Bottom Lug, you’ve connected your Bottom Bracket to the Seat Tube.

• Now you want to connect your Bottom Bracket to the Down Tube. Locking off around the Bottom Bracket again, make a figure eight pattern with the carbon around the Down Tube. Repeat this pattern four times on each side.
• Remember to slightly offset the pattern to maximize coverage, and vary the positioning of your lock off points.


9.3 Carbon-Wrap Lugs | Wrap & Compress Bottom Lug (Spool #2)

• To start the wrap, lock off around the Bottom Bracket shell. This wrap will anchor the carbon around the Bottom Bracket. Keep this wrap tight.
• Wrap around the Chain Stay, lock off around the roughed bamboo. Lockoff points are the softest part of the Lug, so you want to always avoid locking off on the balsa wood, which is already under high stress.
• Now wrap back to the Bottom Bracket, locking off around the Bottom Bracket Shell.

• Remember the Four Laws of Wrapping:
1. Always completely wet the carbon fiber in epoxy.
2. Always lay the carbon wide and flat: avoid it twisting.
3. Always wrap the carbon fiber tight: wrapping it loosely will make your bike weak.
4. Cross the carbon over itself: do not simply spiral it around the bamboo.

• You’ve created a figure eight pattern. Repeat this pattern four times on this Chain Stay.
• Remember to slightly offset the pattern to maximize coverage, and vary the positioning of your lock off points.
• After you’ve wrapped this figure eight pattern four times on this Chain Stay, wrap back to the Bottom Bracket, under the Bottom Bracket, and lock off around the other side of the Bottom Bracket.
• Now repeat this same figure eight pattern four times on the opposite Chain Stay.
• Keep dipping your fingers into the epoxy and rubbing it on the balsa Lug. This will help make sure you’re wrapping wet.
• Once you’ve completed this pattern four times on each Chain Stay, you’ve connected your Bottom Bracket to the Chain Stays.
• Use the remainder of the spool to maximize coverage, using the Four Laws of Wrapping, and remembering to move around the bike so you can see the Bottom Lug from every angle to ensure complete coverage.


9.4 Carbon-Wrap Lugs | Wrap & Compress Bottom Lug (Spool #3)

• Use your fingers to smooth out any lumps in the Lug.
• After you wrap the two spools of carbon on the Bottom Lug, there are often three patches of uncovered balsa remaining: one on the underside of the Bottom Lug, and one on each side. Use a carbon patch on each spot to cover the basla, wetting the patch out with epoxy.
• Use the third spool to wrap over the carbon patches, cinching them down.

• Once this is done, lock off the carbon around the Chain Stay.
• Wrap underneath the Bottom Bracket, and lock off around the Down Tube.
• Wrap underneath the Bottom Bracket and lock off around the opposite Chain Stay.
• Wrap back underneath the Bottom Bracket, and lock off around the Down Tube.
• Remember to use the Four Laws of Wrapping.
• This pattern connects the Down Tube to the Chain Stays.

• After you’ve completed this step, continue to wrap the Bottom Lug using the Four Laws of Wrapping, and repeating the patterns described above.
• Now wrap a tight slinky wrap to cinch everything down.
• Lock off around the Chain Stay and slinky-wrap around the Chain Stay, to the Seat Tube, to the Down Tube, and back to the opposite Chain Stay. Make sure these wraps are very tight.

• To finish the Bottom Lug, wrap two circumferential wraps over the top of the Bottom Lug and underneath the Chain Stays.
• Now wrap two circumferential wraps around the back of the Seat Tube and the front of the Down Tube.
• Now wrap two circumferential wraps between the Chain Stays and around each side of the Bottom Bracket shell.

• We recommend at least three spools of carbon fiber for the Bottom Lug. For larger bikes and larger riders, 4 or 5 spools should be used.

• Once you’ve completely covered the Bottom Lug with at least three large spools of carbon fiber, use your hands to compress the Lug.
• Holding the Bottom Lug in both hands, move one wrist forward and the other back, squeezing out any extra resin.
• Wipe off any excess resin with a rag.
• The Bottom Lug will feel firm to the touch if properly wrapped.
• Wait 15 minutes.
• Now begin to compress with the compression tape, adhesive side UP.
• It’s very important that you pull the tape as tense as possible. Push the compression tape to its limit.
• Keep the tape flat. If the tape cuts into the Lug, this will induce a stress concentrator which will later need to be removed with excessive filing, removing too much carbon.
• Wrap as tight as you can without wrinkling the compression tape.
• Wipe off any excess resin with a rag.
• Leave this tape on for 2.5 hours.


9.5 Carbon-Wrap Lugs| Wrap & Compress Seat Lug

• From your earlier filing and sanding work, the dried resin should be as smooth as possible.
• There should be no sharp pieces of resin that will act as stress concentrators in the Lug.
• With your gloves on, wet out the entire Seat Lug to the roughed areas on the bamboo.
• To start the wrap, lock off around the Top Tube. This wrap will anchor the carbon around the Top Tube. Keep this wrap tight.
• Wrap along the the side of the Seat Lug, over the top of the Seat Stay.
• Lock off around the roughed bamboo of the Seat Stay. Lockoff points are the softest part of the Lug, so you want to always avoid locking off on the balsa wood, which is already under high stress.
• Now wrap along the same side of the Seat Lug, wrapping over the tope of the Top Tube.
• Wrap around the Top Tube and lock off.
• Come underneath Top Tube and along the same side of the Seat Lug.
• Repeat this step 7/8 times, offsetting to achieve maximum coverage. This pattern connects the Top Tube to the Chain Stay.

• Repeat this pattern on the other side of the Seat Lug, connecting the Top Tube to the opposite Seat Stay.

• As you near the end of your first spool of carbon fiber, lock off on the Seat Stay and wrap around the back of the Seat Lug, passing the fiber along the side of the Seat Lug.
• Continue to wrap the fiber around the Top Tube, lock off, and wrap around the other side of the Seat Lug, across the back of the Seat Lug, and around the opposite Seat Stay. Lock off on the Seat Stay.
• Repeat this step several times to achieve maximum coverage.

• Use the second spool of carbon fiber to achieve full coverage of the Seat Lug.
• Lock off on the Top Tube, wrap wide, and aim to cover the entire Seat Lug using the Four Laws of Wrapping.

• Use the third spool of carbon fiber to repeat the original set of patterns for wrapping the Seat Lug.
• Lock off on the Top Tube, and use long figure eight patterns to reinforce the Seat Stay to Top Tube connection.
• Repeat this pattern at least three times on each side of the Seat Lug, using the Four Laws of Wrapping.
• You’re trying to fill in all areas of the Seat Lug to make a nice, smooth surface.

• Once you’ve completely covered the Seat Lug with at least three large spools of carbon fiber, use your hands to compress the Lug.
• Holding the Seat Lug in both hands, move one wrist forward and the other back, squeezing out any extra resin.
• Wipe off any excess resin with a rag.
• The Seat Lug will feel firm to the touch if properly wrapped.
• Wait 15 minutes.
• Now begin to compress with the compression tape, adhesive side UP.
• It’s very important that you pull the tape as tense as possible. Push the compression tape to its limit.
• Keep the tape flat. If the tape cuts into the Lug, this will induce a stress concentrator which will later need to be removed with excessive filing, removing too much carbon.
• Wrap as tight as you can without wrinkling the compression tape.
• Wipe off any excess resin with a rag.
• Leave this tape on for 2.5 hours.


9.6 Carbon-Wrap Lugs| Wrap X Pattern

• From your earlier filing and sanding work, the dried resin should be as smooth as possible.
• There should be no sharp pieces of resin that will act as stress concentrators in the Lug.
• With your gloves on, wet out the entire Head Lug, around the Head Tube and up to the roughed areas on the bamboo.
• To start the wrap, lock off around the Down Tube. This wrap will anchor the carbon around the Down Tube. Keep this wrap tight.
• Wrap around the Head Tube, and then spiral your wraps up to the Top Tube.
• Remember to use the Four Laws of Wrapping.
• Lock off on the Top Tube over the roughed bamboo.
• Wrap around the Head Tube, and then spiral your wraps down to the Down Tube.
• Lock off on the Down Tube
• Repeat this wrap pattern, offsetting by about 1 cm to ensure maximum coverage.
• Try to keep your wraps as symmetrical as possible, so you cross on the Head Tube at the center line of the bike.
• You’ll get to a point where you can’t get any more coverage using this wrapping technique.
• When this happens switch your wrapping pattern, so you go from wrapping around the inside of the front triangle to wrapping around the outside of the front triangle.


9.7 Carbon-Wrap Lugs| Finish Head Lug Wrap

• As you start your second spool of carbon fiber on the Head Lug, lock off on the Top Tube.
• Spiral your wraps up the Top Tube, and get as close as you can to the Head Tube.
• Remember the Four Laws of Wrapping.
• Now wrap straight down to the bottom of the Down Tube.
• Keep this wrap a little looser than you normally would, because you’ll likely be wrapping over air in this step, and you want to be able to cinch it down later.
• Continue the wrap up the other side of the Head Tube to the top of the Seat Tube.
• Repeat this wrap again, coming over the top of the Seat Tube, down the side of the Head Tube, and around the bottom of the Down Tube.
• Once you get to the top of the Seat Tube, wrap around the front of the Head Tube and cinch the wrap around the Head Tube between the Top Tube and the Down Tube.
• Work your way down the Head Tube between the Top Tube and the Down Tube, cinching the carbon fiber as you go.

• Now continue to wrap the Head Lug with long spirals, using the Four Laws of Wrapping, aiming for complete coverage of the Head Lug.


9.8 Carbon-Wrap Lugs| Compress Head Lug

• Once you’ve completely covered the Head Lug with the four 22g spools of carbon fiber (88g total), use your hands to compress the Lug.
• Holding the Head Lug in both hands, move one wrist forward and the other back, squeezing out any extra resin.
• Wipe off any excess resin with a rag.
• The Head Lug will feel firm to the touch if properly wrapped.
• Wait 15 minutes.
• Now begin to compress with the electrical tape, adhesive side UP.
• It’s very important that you pull the tape as tense as possible. Push the electrical tape to its limit.
• As you wrap the tape along the inner triangle, it’s very important that the tape lies flat.
• If the tape cuts into the Lug, this will induce a stress concentrator which will later need to be removed with excessive filing, removing too much carbon.
• Wipe off any excess resin with a rag.
• Leave this tape on for 2.5 hours.


Bike Making FAQ
Step 8: Prepare Lugs for Wrapping | Step 10: Finish Lugs