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:

just finished the first layer of twine

just finished the first layer of twine

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.

steer tube, clearly so far from done

steer tube, clearly so far from done

bottom bracket

bottom bracket

drop outs, these are by far the easiest to wrap

drop outs, these are by far the easiest to wrap

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:

not so straight

not so straight

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.

eek! it was pretty stressful to cut this

eek! it was pretty stressful to cut this

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

with a spacer that pushes the left seat stay to a better angle

with a spacer that pushes the left seat stay to a better angle

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

heat tube, after sanding the first layer

heat tube, after sanding the first layer

drop outs, after sanding the first layer

drop outs, after sanding the first 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).

adding epoxy/hemp to the seat lug

adding epoxy/hemp to the seat lug

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.

wrapped with electrical tape

wrapped with electrical tape

you go through a lot of tape, so get the cheap stuff

you go through a lot of tape, so get the cheap stuff

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

perforating electrical tape

perforating electrical tape

after second layer

after second layer

second layer sanded

second layer sanded

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.

closer, but still a long way off

closer, but still a long way off

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.

I put to tape too close and used a craft knife to slowly whittle it all away

I put to tape too close and used a craft knife to slowly whittle it all away

the PVC fittings are pretty well-potted, but at least the bottom bracket threads are clean

the PVC fittings are pretty well-potted, but at least the bottom bracket threads are clean

bottom bracket, lots of cleaning up to do

bottom bracket, lots of cleaning up to do

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4 thoughts on “bamboo bike Part 3: lugs

  1. its pretty impressive work. one question : Did you directly join the wood to metal or the wood pipe is fit into a metal cylinder?

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