The process of laying up the moulded lugs requires the same preparations as wrapped lugs. Make sure your space is clean, free of clutter and contaminants, that you’ve taped down your plastic worksheet, and that all the tools you need are readily at hand. Make sure you’ve got your respirator and your gloves.



Again, plan your layup schedule, all the pieces you need, where they go, and how they’re oriented. Draw it out on a sheet of paper and tape it up on your wall for reference so you don’t get lost midway through.



The inside of your lug moulds will have some pretty odd contours, so without a little bit of trial and error it’s difficult to tell what size and shape you should be cutting your plies out in order to fit. There is software that can help you “unwrap” surfaces with compound curves and project them onto a flat template for fabric patterning, but the easiest way is probably just to use a (clean) rag and incrementally trim it until it fits neatly into your mould.



In order to make up the 2.5mm wall thickness in my moulds, my layup schedule consisted of:

1. 0/90 8HS satin carbon fiber

2. +45 UD CF

3. -45 UD CF

4. 0/90 8HS satin carbon fiber

5. 0 UD CF (not on gusset)*

6. 0 UD CF (not on gusset)*

7. 0 UD CF (not on gusset)*

8. 0/90 fiberglass



You want to transmit the bending loads through the tubing of the entire frame, so the majority of the reinforcement is in the 0 degree axis. The +-45 degree reinforcement is important to resist torsional loads, but you’ll find that I haven’t added any additional 90 degree plies, except for the fibers in my woven plies, as hoop strength is not critical in these joints (certainly not when your laminate is 2.5mm thick, anyway!).



For the +-45 degree layers, I used unidirectional fibers for my first several layups. Because the UD tape is not woven, there is no stretch in it and it does not conform to compound curves well. To prevent the tape from bunching, I cut each piece into a series of thin longitudinal strips so that I could lay them manually. For the bottom bracket, however, I decided to use the 8HS satin weave CF cloth cut on a +-45 degree bias. This made layup and handling much easier, so I would recommend it.



*The final axial plies are cut to fit around the lug itself only, rather than across the entire flat gusset area of the mould. This is necessary to build up the extra 1.25mm wall thickness required to fill the mould in these areas.



It's important to ensure that you have the right number of plies to produce the correct wall thickness of carbon fiber in your moulds, so to verify that you've calculated it right, you can pinch your plies with a set of digital calipers and see if you've got the correct thickness (or slightly thicker, since it will be compressed in the mould).



Note that because I’m laying the cloth into the mould rather than onto the frame, the order of the layers is reversed, and I put the fiberglass into the mould last. Alternatively, you can also wrap the fiberglass directly around the metal tubing on frame in advance of clamping your moulds on.



Once you have your pile of plies cut into the right shapes laid out on the table, you can begin the layup process, as described earlier. Prep your surfaces, wet sand epoxy into the metal tubing, and isolate all metal parts with a layer of fiberglass. Mix up multiple small batches of epoxy throughout the layup so that they flow and wet out the cloth well, and squeegee off excess resin to reduce weight and allow better laminate compaction. Before you put your first ply into the mould, spray mould release agent into your waxed moulds – polyvinyl alcohol is commonly used industrially, but cheap extra hold hairspray works well, too! When you are laying the pieces into the mould, make sure they conform to the mould smoothly and don’t have folds or bunches. This is tricky on the first ply, since it will stick to your gloves better than the mould, so getting it to lie properly is more difficult than with later layers.



Once you’ve laid all your plies into both of your moulds, carefully align one half of the mould with your joint and press it in place. Then place the other mould. Use multiple clamps to evenly distribute the clamping pressure across your moulds, and tighten them all incrementally so that the moulds are parallel with a uniform gap in the middle.



Once you’ve clamped the moulds, take a razor blade (or pair of metal scissors that you can clean off with acetone afterwards) and cut off as much excess flashing around the joints as you can. Sometimes this can be more easily done after a few hours when the epoxy has gelled but not yet cured to a rigid solid.



Start with the least complicated joints to build up your confidence and familiarity with the process. I started with the chainstay wishbone, then did the head tube lug, then the seat tube cluster, and then finally ended with the bottom bracket lug, which is the most involved of the layups.



N.B. When doing the bottom bracket and headtube lugs, make sure that you don’t get epoxy inside. In both cases I filled the tubes with a thick coating of grease, placed electrical tape over any drainage holes, and inserted printed caps into the openings.