bamboo bike Part 3: lugs

With all the tubes tacked in place on the jig, I could start wrapping the lugs. This is a crazy messy business, so I wrapped everything besides the lugs in tape and plastic to minimize the epoxy clean up later. Here’s the frame with the first layer of epoxy on it:

Definitely not ready to ride yet! I was pretty scared of getting lots of voids so I started off with really small layers. This build in general was definitely a test of patience since I did so many layers before the lugs were done. I’m sure I could do it much faster the second time around, but I still marvel at how some shops offer programs where you can build a whole bamboo bike in just one weekend.

So, before doing this first layer of twine/epoxy, the seat stays were already crooked. This is because I used electrical tape to bind them in place while I tacked them with 5 min epoxy. Of course, when I came back 20 min later, the tape had pulled them off to an angle. I was scared to fix the angle before the first layer, since I was afraid that I might break other joints in the process of fixing this one.

As you can see in the image below, both seat stays are shifted to the right:

My solution: cut the left one and pull it out towards the left. You can see from the clearance to the wheel (which is currently mounted in the drop outs) how bad the shift is.

I glued in a spacer to keep the seat stay out the right distance.

With the seat stay angle fixed, I sanded all the lugs to prepare for the next layer.

This is probably the only in-progress photo I have of building the lugs since its such a messy process. I wear epoxy-coated gloves the hole time and try not to touch things I care about (like my camera).

Below you can see I cut ~10cm long sections of twine. I then untwisted the fibers a little so that they would lie flatter and it was easier for me to massage the epoxy into them. I found it was easiest to lay on a bunch of 10cm lengths of twine, and then wrap over them with 2-3 ~60cm lengths of twine (also untwisted and pre-coated with epoxy).

After each layer of twine, I wrapped electrical tape all over the joint. I read somewhere on the internet that epoxy doesn’t stick to electrical tape. Not sure why, but I found that to be true. At some point I also read (I forgot where) that its better to wrap with the non-sticky side inward. I forget the reason exactly, but its probably because the adhesive on the tape isn’t going to stick to a wet epoxy surface, so you might as well flip it inside out so it can stick to itself when you wrap.

Its a good idea to perforate the electrical tape so that excess epoxy can squeeze out.

At this point its strong enough to take out of the jig. Although, you might want to leave an axel/hub between the rear drop outs so you don’t accidentally smush the rear triangle.

The blue tape worked for the most part to keep things clean, but I underestimated how large I wanted the lugs in some cases. This led to me slowly and carefully whittling away the bits of tape caught under the epoxy.