aprhockey

Built my first bamboo bike this summer. Built it up as a fixie because I unfortunately didn't have enough clearance to fit a freewheel due to the bulky joint at the dropout. Anyway, here is version 1.



After about 125 miles or so, I heard a distinct crack while I was riding it. It was still rideable so I got home and inspected it then. I couldn't find a crack on any bamboo pole or at the joints. I could feel that the bottom bracket was a little more flexible than before though.

I thought I would repair it. Since I was going to go through the trouble of grinding down the joint, I thought maybe this would be a good opportunity to replace the seat tube entirely. The first time around, I actually glued the seat post directly into the bamboo. I wanted to do it correctly this time around. I finally found a piece of bamboo that would work and proceeded to grind down the joint at the BB and the seat tube cluster. You can see my flickr to see more shots of the process. Here is the repaired bike:



After I had finished the first fiber/epoxy layer on the new joints, the new section of bamboo split in the middle section from node to node. I put the bottle cage mount with fiber wrapping it to try to inhibit the crack from growing and to cover it up.

Anyway. After about 90 kilometers on the repaired bike, it became too flexible to ride. On closer inspection I noticed that major cracks had formed at the down tube / head tube joint and at the top tube / seat tube joint.





It's hard to see in the second picture because I didn't finish the joint as nicely as the head tube. The crack follows the miter of the top tube.

My question for you guys is why? I'm not sure why these joints have cracked. What am I doing wrong? Could cold weather affect the epoxy enough to cause these cracks? While using the repaired bike, I left it outside at all times. The temperature ranged from about 0C to 18C in about 1 weeks. I had a minor crash that put a little bit of damage on the right side of the head tube. Could that have been enough to initiate a crack through the epoxy? Would it be worth it to grind down the two cracked joints and rewrap them? Or will there just continue to be problems due to something I did wrong? It is really frustrating that I can't get this bike to work. I would love any and all help.

TL;DR I built a bamboo bike that broke. Then I repaired that bike and it broke again. I don't know why.

cbchess

I've heard that hemp will eventually fail. I used carbon fiber tow and also built up my joints alot more than you. Another thing you could do would be do the joints FIRST in a fiberglass cloth then finnish with hemp.
the cloth will make the joints a ton stronger.

RaleighSport

CB's right, I wanted to use hemp too but it's way too naturally flexible.. and with everything I know so far, once there's a crack that's it it's gonna get worse and worse... the fiberglass/cf layup seems to be the most successful, as well as having several well aged bamboo pieces that have already been sorted out to ditch any with cracking..

squirtdad

I don't know about bamboo bikes....but from surfboard and kayak goofing around with fiberglass, the materal at the joints (hemp?) does not appear to have been really wetted all the way through with resin and than had the excess resin removed. Also The materal also does not appear to have any structure, and is more a mat. Just looking at it it does not look like a sound joint as there is no oriented reinforcement to handle the stresses (think about how you use an ace bandage on an ankle) and the resin does not look to be fully engaging what reinforment material there is.

aprhockey

I'm still not sure what to think about hemp vs. carbon fiber or fiberglass. There seems to be some contradictory opinions out there. Calfee moved away from carbon fiber because the thermal coefficient of expansion was too different from that of the bamboo. The Bamboo Bike Studio has moved away from using hemp lugs because it is weaker and tends to stretch more and more over time.

squirtdad: When the joint failed initially on the first version of the bike, the epoxy had not completely soaked through the fiber. When I rewrapped the joints after replacing the seat tube, I tried to make sure that the fiber was thoroughly soaked. What makes you say it looks like it hasn't been wetted all the way through? I'm not even sure if we're talking about the same things here. I did find it very difficult to work with the hemp. I bought raw, long, uncombed hemp fiber here. I rolled the fiber between my hands to try to make segments of rope sort of like making dreadlocks. But I found that it was hard to wrap this very tightly around the joints. Here is a picture of the hemp fiber being wrapped around the dropout the first time around.



Is there a way to ensure that the fibers are thoroughly wetted? Is there an easier way to work with raw hemp fibers? Do I need to treat the hemp fiber in anyway? I think I will probably switch to carbon tow for the next bike I build and since I have a lot of hemp left do a finishing wrap with hemp fiber like cbchess mentioned.

Does anyone have experience with bamboo bikes in cold weather? I live in Montreal for the school year. If I built a new frame using carbon tow do you guys think I would be able to ride it through winter?

Allen

I second this.
Your fibers are not fully wetted nor do they appear to have been compressed.

Here is an example of a fully wetted and vacuum bagged lug. Note how Calfee alines the fibers.

You want the fibers to be fully coated with resin and you want to compress the lug in some fashion to remove air bubbles, voids, and excess resin.

RaleighSport

I can't remember who said it, but one of our forum members puts the hemp through a couple of cycles in the dryer to make it more absorb more of the epoxy (I don't really understand the fancy part) but it frays it up a little bit and makes it better able to suck of the epoxy in my understanding, how many layers is your hemp? What did you use for compression? I know if you're vary careful with CF you can compress the layers with reversed electrical tape punctured to let the excess epoxy bleed off.. not sure anything shy of vacuum bagging would hold up for long with the hemp though, mind you I could easily be wrong but nothing I know of will do it like that.
Edit:
Allen, Calfee sands down all his joints doesn't he?

Allen

Yes he does. He overbuilds them and then shapes them with a drimmel

I was able to get away with using the electrical tape trick on my first bamboo frame but still had to shape them afterwords to make them look presentable.

RaleighSport

I think it was his DIY article on the CF Bamboo bike that got me into this in the first place.. but that guy knew a lot more starting then I do atm.. so of course his lugs are gonna be gorgeous!

Allen

Some show on Discovery had a 10 min spot showing his bamboo bikes. That was my first inspiration.

Contour

I've got a couple questions about your methods.

1st, how did you bond the bamboo to the other bamboo or metal components? Did you roughen the surfaces, how well?

2nd, Are you sure that there were no cracks (even really small ones) before you even assembled the bike? The constant fatigue from cycling could have caused the crack to slowly grow.

3rd, Are you wrapping like you show on the dropouts? How many layers like that did you do before applying the epoxy?

4th, Is the Epoxy mixed at the right ratios?

5th, How tight were the miters to the bamboo or metal components?

squirtdad

I would defer to the guys who have worked with the material.....but if put on a spot and I had to build a bike to get off a desert island, based on messes I have made with fiberglass before (building surfboards, fixing kayaks when they weren't plastic) I would not twist the hemp into rope/twine/dreadlock. i would comb it and make bands of fibers. I would dip the fibers in resin to soak, run between gloved hands to get excess resin out and apply to the joint, layer by layer, with different fiber orientations for strength. this will take a slow cure mix for the resin. at the end I would vacuum bag (you can get pretty creative with a shopvac or use some other method (the backwards electical tape ?) to compress the joint, pushing the fibers into a denser material, and getting rid of excess resin.

Canaboo

I've built many bikes that have had no trouble coping with weather extremes in Canada without cracking.
Make sure you pop the nodes out of the inside and coat the inside and outside with epoxy. It's best to use poles that you know have survived a number of cyles of hot/cold/damp/dry cyles without cracking.
A more reliable source of natural wrapping is Manila rope that has been unravelled and washed/dried.
Wrap and paint epoxy on as you wrap to thoroughly saturate the matrix. Wrap your lug tightly with strips of innertube to compress and squeeze the resin deep down into the fibers. After it is wrapped tightly, fill a syringe with Epoxy and inject it deeply into all sides of the lug that you may feel aren't quite wet out.
Wrap it one more time to limit how much resin seeps out of the holes you have punched.
Warm the lug with a hairdryer briefly to improve the resin flow throughout the pressurised matrix..
Let it cure overnight and then shape it with rasps and sandpaper. Coat it again with Epoxy to get a smooth finish. Generally it is best to use a UV resistant varnish on top but you can use a surfboard Epoxy which has better UV resistance if you don't anticipate your bike sitting directly in the sun for extended periods.
It is always best to really pay attention to your final coats of finish if you want the bike to last through extremes. Three coats of Epoxy and two of a good clearcoat or varnish, just like you would use on a cedar strip canoe that you want your grandkids to enjoy.

aprhockey

I'm not sure why the joint at the seat tube isn't fully compressed... I did wrap the joint with reversed, perforated electrical tape. I'll use innertubes and be more careful next time.

1: To bond the bamboo to the steel head tube for example, I mitered the bamboo to fit snugly. I filed all the paint off of the head tube (it was cut from another frame) then used the edge of a metal file to try to score the metal randomly. I used sandpaper/files on the bamboo until the waxy surface was gone. I probably should have used a rough rasp. I used West System 105 resin and 205 hardener mixed with 404 high density filler until it was pretty thick to tack the frame together. Thick enough that it wouldn't drip from an applicator stick.

2: Were there cracks in the bamboo? There was one crack on the new seat tube as mentioned in the OP. Cracks in the epoxy, I don't see why there would be in the seat tube / top tube joint since it hadn't been loaded before assembly. The joint at the head tube that cracked..... it's possible there was a crack before. I didn't look at it very closely.

3: On the new joints I wrapped I did two layers with a 'rope' probably about 2/3 of the width seen in the picture. I painted epoxy onto the joint area, wrapped the fiber, applied epoxy to the fiber using a mixing stick. I tried to really work the epoxy in with the mixing stick to the point where if I pressed on the fibers, a bit of epoxy would bleed out.

4: I used the corresponding pumps for the resin and hardener so assuming they were working properly, then yes, the epoxy was mixed in correct ratios.

5: All of the initial miters were pretty good. There may have been a few small gaps (<0.5 mm) along the miter line. The miters of the top tube and seat stays along the new seat tube were all off because I had to make room for the new piece to slide in. I tried to make up for that by tacking the seat tube cluster with very thickened epoxy.

Canaboo: To coat the inside of the bamboo, should I just pour some epoxy into the pole and roll it around for a while? I will definitely buy a syringe, I feel like that would have resolved most of the problems. About the final coats... I should coat the entire frame with 3 coats of epoxy? I think I read in another thread that you suggested that hemp fiber should be washed prior to use to get rid of all the oils on the fibers. What's the best way to wash a bunch of hemp fiber? Put it in a pillowcase and throw it in the laundry machine?

Also, is it necessary to do a final sanding/shaping of the joints?

For anyone interested, here is the album showing the build process the first time around.

You guys are a huge help. Thanks for everyone's input.

fixedgear80

Looks like a good learning experience. Take all this useful information and try again. Think of this as your first prototype! I'm guessing a combed hemp fiber will allow you to create a tighter matrix/combo of hemp to resin. Over build all the lugs first and then shape them to the desired look. A very important step is properly mitering all the joints first.
For my first bike I will be using a doner bike for all the lugs then simply overlapping the bamboo over the steel parts! Watch this series of videos!

RaleighSport

passing thought, has anyone tried taking green bamboo that fits about perfect over the metal without mitering, then heat treating and allowing to age cure on the bike? I'm wondering if you could correct any allignment issues down the road with a rubber mallet before tacking/wrapping! hmm probably just another of my half baked ideas.

cbchess

I agree your hemp wrap looked way too fluffy and loose. You need much tighter lugs. And many more layers for strength. With carbon fiber tow, I was able to alternate wrapping directions with round and round wraps and then long pieces running the length of the joint. Then round and round again. I would do this until the whole joint was spongy and then wrap super tightly with electrical tape for compression until dry. After drying, sand and repeat. I would say I did each joint at least 4 or 5 times of full many layered wraps and then drying and sanding. It looks like you did you joints once or twice. So with my frame each joint had like 20 layers on it. After a test ride I added like 10 more layers to the head area.
I am still going to add a few more layers to the seat cluster and BB area.

Italuminium

Just curious, not a builder myself, but the other day I was walking down the market and noticed a few stalls selling all kinds of cloths and tapes out of linen and hemp cloth - both treated and untreated. Could it be possible to build a frame of bamboo by laminating thin strips of cloth? Or is a lot of strenght lost in the processing and weaving of the fibers?

RaleighSport

I think if you look back in this thread itself you'll see manilla linen I think it was, was suggested as a viable alternative to hemp. I don't know why, but the consensus is raw hemp fibers are better then any other choice of hemp when working it for making bamboo bikes.

Dan The Man

What was recommended was unwound manilla rope, not manilla linen

RaleighSport

Thank you for the correction I'm all over the place today.

Canaboo

You can use artist's canvas made with Belgian linen to do a cloth matrix wrap that will look vaguely like carbon cloth.
There is actually a company that makes Carbon/Linen bikes with the layers blended. Good linen that has been processed properly is extremely strong and generally processed much better than Hemp. It also suffers less from residual oil.
You can buy high grade Linen tow from Gemini fibres in Canada.

Canaboo

You can use artist's canvas made with Belgian linen to do a cloth matrix wrap that will look vaguely like carbon cloth.
There is actually a company that makes Carbon/Linen bikes with the layers blended. https://www.museeuwbikes.be/
Good linen that has been processed properly is extremely strong and generally processed much better than Hemp. It also suffers less from residual oil.
You can buy high grade Linen tow from Gemini fibres in Canada.

aprhockey

I think you guys have given me the confidence to build another frame over my winter break. I'll post up pics of it when I'm done to see what you think before assembling it.

squirtdad

Just out of curiosity....why hemp/manilla/or linen vs carbon fiber or fiberglass? Structural? Aesthetic? I don't see how natural can be used as a factor when epoxy resin is also being used.