This while riding the streets of Oxford, late for rowing, I was pounding on the pedals to get out in front of a car. In one stroke, the chainring collapsed, leaving me not only powerless, but brakeless as well! Once I footjammed my way to a stop, I surveyed the damage.
Looks like the bolts had come loose.
I picked up a digital SLR camera today for only £175 ($280). Its an Olympus E-510, which was a great mid-level prosumer when it came out in 2007, and still has all the features I need. It was only used twice, and is only a year old.
Why did someone buy a $1000 camera only to use it twice? It makes me wonder how much better the world would be if the consumerism in our lives was based around leasing, renting or time-sharing nice things. It would encourage manufacturers to build our things with longevity in mind, and as soon as you realize you don’t use that guitar or table saw as much as you thought you would, then you can just return it and save on your monthly “stuff” bill.
Anyhow, enough rambling, here is a shot of whambam outside a pub in Oxford. It is processed in pseudo-HDR.
After riding WhamBam a few times, it has quickly become apparent that there is not enough ground clearance under the pedals when cornering. This was due to the fact that we didn’t use a jig when assembling the frame. I made plenty of calculations for the appropriate geometry, but in the end, we more or less had to eyeball the angle between the forward triangle and the chain stays. The clearance is not too bad, except for the fact that I was intending the bike to be a fixed gear, which doesn’t allow you to coast with the outside pedal down during hard cornering. This left me with two options, either go with shorter cranks, or scrap the fixed-gear idea. I went with the later option.
My first thought was to swap it over to a single-speed, especially since the wheelset I was using already had a flip-flop hub and a freewheel on one side. However, this would require building a brake mount into the seat stays, which would apply a force right in the middle of the seat stays, perpendicular to the load they were intended for. The would probably be strong enough, but without load testing, I wouldn’t really be comfortable with that setup. Imagine the catastrophic failure potential: blowing out the seat stays under heavy braking… not good.
So then I settled on a coaster brake, which would require a new rear wheel. This is the result:
In order to waterproof and otherwise protect the bamboo, I finally decided that I would have to put on a coating. I really loved the look of the bare bamboo, but after I got my first scratch, I decided for the good of the bike I would have to put on a protective coating. Since I had lots of epoxy, I went with an epoxy coating. I sanded the all of the bamboo surfaces with 80 grit wood sand paper, and wiped the dust off with a damp rag. Then I mixed up a batch of high optical clarity epoxy, and diluted it 50/50 with acetone. The acetone thins the epoxy out, and helps it to get absorbed into the wood. It took more than 24 hours to set, and I am really happy with the result. It created a much deeper, more saturated luster, with a little gloss to it.
While I was at it, I also had to repair the seat post mount. The original method I used to mount the seat post turned out to be highly ineffective. Basically after about an hour of riding, the bond between the piece of steel and the carbon broke.
Old seat post mount: 
I rebuilt it by cutting off the top 2cm, wrapping a seat post in a non-stick tape, and laying up some carbon. Once it cured, I cut the carbon with a hack saw to create space for the clamp to squeeze the tube. Hopefully this will work.
After the epoxy had set, I was ready for the finishing touches. I sanded down all the joints with 80 grit sandpaper to smooth them out, then applied a second coat of epoxy for a nice finish. Once that had set, I put on the bottom bracket, cranks, pedals, wheels and chain, and I was all done!
Here are a few close pictures of the joints
Since I didn’t have my choice of donor bike, the head tube is too short for me. To overcome this, I got a $20 fork with a long steerer tube, and made a nice looking bamboo spacer. Now the bars are the right height. Unfortunately, I think I grabbed a fork for a 27inch wheel, which is designed for a front wheel that is 14mm smaller in diameter then the 700c wheels I am using. I was able to file it down to fit, but I can’t fit it with brakes. I will replace it with a 80s carbon fork. They occasionally come up pretty cheap on eBay, they look pretty cool, and they are light weight. I can’t use a standard fork, because the head tube is for a 1 inch threaded fork rather than the standard 1 1/4 inch threadless.
The bike weighs in at 21.5lbs. Thats fairly light, but heavier than I was aiming for. The fork I have on right now is very heavy, so I should be able to shave 1.5 to 2 lbs with a carbon fork, bringing it into line with what I was going for. It has now joined my stable.
Once the frame was tacked with 5-minute epoxy, we were ready for the layup. Here is what you will need for a wet layup:
1. Carbon fiber tow, basically 5mm wide unwoven carbon fiber (find it on eBay)
2. Epoxy resin and hardener suitable for use with carbon fiber
3. 100 grit sand paper
4. Cheap paint brushes (get at least 5, you will throw one out after every batch of epoxy sets)
5. Lots of pairs of gloves
6. Plastic masking material
7. Ideally a gram scale, but disposable volume measures will due (such as shot glasses)
I would have taken more pictures, but with wet epoxy everywhere it was a real challenge.
Start by mixing up a batch of epoxy. Be sure to follow the directions because mixing ratios vary. Also, you should be well aware of the working time, as it can range from a couple minutes to a few hours.
Next you should paint it onto the part. The surfaces should all be rough, so sand first if necessary.
Then wrap the wet surface with carbon fiber tow until it starts to look dry. Wrap a couple more layers and then paint on some more epoxy. It is easiest if you spool off 20 or 30 meters at a time onto a smaller spool so you can get around tricky corners. They key is to ensure that you wrap in all the directions where load is expected to be applied. Remember, carbon fiber is only strong in the direction of the tow, so if you don’t wrap in a direction where load is applied, the joint will fail.
The wet layup took about 4 hours, and the working time for the epoxy we used was just over an hour, so we made three pots. After 48 hours of curing time, the joints were strong!
Once all the sections of bamboo have been heat treated, cut to length and mitred, and once the metal sections have been prepped, then you are ready to prep the frame for a wet layup. A wet layup takes several hours, and requires the frame to be held at different angles and loads to be applied as the carbon is laid up. To ensure that you end up with a nice straight frame, you need to create solid bonds at each joint.
First we had to figure out how to get the frame to be straight in all the appropriate dimensions. If we end up building more in the future, then we will build a jig, however I think for a one-off a jig is a bit overkill. That being said, a using a jig is really the ideal way to do this step, so the following is not so much a set of instructions as it is an explanation of how I tacked my frame together. Please take that into consideration if you make your own bamboo bike.
I had decided to use the steel chain stays from the donor bike partly because of the tension, compression and torque loads that are applied on them when riding, and also to help with getting the whole bike to be straight and true. It was a trade-off because I had to compromise with a longer than desirable wheelbase, and I would have liked to build the whole bike out of bamboo (I even treated, cut and mitred bamboo chain stays), but in the end I think I made the right choice.
We (Jame Kay, who was invaluable in this phase of the build, and I) started by tacking the seat tube the bottom bracket shell, which was conveniently already attached to the chain stays. To get it to set straight, we put on the rear wheel, put a spacer between the wheels and the seat tube, and sighted from behind the wheel to ensure it was straight up. Once we were satisfied this would work, we popped the seat tube off, slapped some 5-minute epoxy on the joint, and then taped it all in place. Read the rest of this entry »
Last night Jame Kay and I put together the frame and did the wet layup. I will do a complete post later, but for now you can look at the pretty pictures. Read the rest of this entry »
To ensure a strong frame, you need to mitre the joints well, and it is a fairly challenging process. When you join two square objects, it is pretty straight forward. You just cut a straight line and bam! you are good to go. Joining two tubes is more complicated, since you have to cut a curve into one so that they fit. When those tubes are different sizes, not perfectly round, and several join together at different angles, things get a little tricky. For this stage in the build I relied on my good friend Nicholas McFarlane and his dad John, who have a basement full of wood tools and a great deal of expertise.
After a little brain storming, we decided to use a drill press. By using a hole cutting bit, we were able to drill a hole the size of the tube to be joined to and at the correct angle. Since the angles were all fairly rough, and I was cutting everything over length to allow for fine tuning later, the process only took an hour or two once I got going (after some excellent training from the McFarlane’s of course). Essentially the steps are as follows:
1. measure the size of the tube to be joined to and select the right bit size
2. measure the angle and set up that angle on the drill press
3. drill out the desired hole size at the desired angle
Next I had to measure it all up again, and file by hand to create a perfect fit. This took a long long time. Seriously, it took a while. But in the end, I think did a pretty good job.
