After years of riding, the frame is still okay and I am still alive too, although I prefer riding my bike equipped by the bamboo/carbon frame, which I have built using the same method described here. Until now, several frames have been built by this method in the world.
Step 1: Few important things you need for building the carbon frame
2. Metal parts - they include an aluminum bottom bracket shell, head tube, short seat tube, cable stops, rear dropouts and a rear brake bosses. The used thin walled tubes and cable stops were made on a lathe, for the carbon frame I have purchased rear dropouts and brake bosses from the bike parts supplier. I have made them by water-jet cutting for the bamboo frame. I prefer to use 7075 Alloy for the metal parts. It is good to have all aluminum parts anodized, as then you do not need to wrap a light layer of fiberglass around the aluminum tubes and part of the rear dropouts as an insulation between the aluminum and the carbon against galvanic corrosion.
3. Foam core - I have used polystyrene foam to make the core of the carbon frame. But it is better to use extruded polystyrene, or polyurethane foam, which is more rigid. Later I have used the polyurethane foam which is normally used for insulation of the outer walls of buildings.
4. Materials for laminating - I have chosen a bi-directional woven carbon cloth (180 grams per square meter). I have used MGS's L285 epoxy resin with hardener 285 for laminating. For the carbon frame I used about 3.8 sq.m of the fabric, for the bamboo frame about 2.0 sq.m. You can also use uni-directional carbon for the base layers and use the bi-directional carbon just for the outer layer.
5. Supplies - I used plastic kitchen foil for covering the workbench during the wetting out the carbon, latex gloves, a small digital scale for weighing of the exact volume of resin and hardener, cups for mixing, paint brushes for wetting out, lots of electrical tape, sand paper and a good respirator during sanding.
6. Patience - the more the better
Step 2: Making the core
I had polystyrene foam rods of the necessary diameters, made simply by using hot wire foam cutter. The cross sections of the main rods was circular, the chain stay and the seat stay were elliptical. I have wrapped these rods with one light layer of fiberglass to increase their rigidity.
In this picture you can see the aluminum parts in their exact position. The polystyrene top tube and down tube is already bonded with carved small pieces of polystyrene for the next sanding. In the front of the picture on the ground the chain stay was being prepared for sanding (to achieve proper shape) and bonding.
Step 3: Making the core 2
After finishing the frame, you can melt the polystyrene out of the frame by using acetone, so you can save about 90 g of the weight. I didn't do so, as I think the core helps to dampen the vibrations and shocks.
Step 4: Laminating
While it was still wet, I have wrapped over the first layer of carbon tightly with electrical tape with sticky side up to provide compaction during curing. I could wrap tightly thanks to the aforementioned light layer of fiberglass, which has increased the rigidity of the foam core significantly. Before wrapping, I have perforated the tape with a pin over the whole surface. This squeezed out excess resin after wrapping.
You can also use perforated heat-shrink tape for the compaction, or use vacuum bagging technique, but for me this was the easiest and sufficient method. According my rough measuremets, the ratio of carbon/epoxy was about 50:50.
This image shows the excess resin after wrapping.
Step 5: Laminating 2
Step 6: Laminating 3
This is the picture after the last layer of carbon. Finally I have let the frame fully cure for a few days at about 50Â°C at the heater.
Step 7: Finishing
Step 9: Building the bamboo/carbon frame
One year later I have built the bamboo frame according the same method as I built the carbon frame. This was a little bit easier, as I did not need to laminate the tubes.
Step 10: Building the bamboo/carbon frame 2
The most difficult part of building the frame was to find quality bamboo rods. It took me much more time than the building itself. I have visited several dealers in near surroundings and I have tried to find appropriate rods of the necessary diameters among huge amount of bamboo. Finally I have found few rods I wanted, but frankly speaking, next time I will build such a frame, I'll rather grow my own bamboo, or fly to Asia for it. The rods for the top tube, down tube and seat tube are some Chinese species of bamboo; I was not very satisfied with the quality of the surface, which was rather scratched and there were also a few woodworm holes in it. The rods I have selected for the seat and chain stay were some other species from Malaysia. Unfortunately the seller was not able to tell me what species it exactly was. During breaking tests of these bamboo rods I found out that when I filled the inside with the polyurethane foam (which added only few gram of weight), the rigidity increased mainly of the rods for the seat and chain stay, which are the most critical parts of this frame.
Step 11: Building the bamboo/carbon frame 3
The frame building itself was quite quick. I have used the frame jig I made for my previous carbon frame. Bamboo rods were fitted in miter joints together with aluminum tubes (bottom bracket shell, head and short seat tube) and bonded with epoxy. The junctions in the rear part of the frame I have made from polyurethane foam and the following laminating process of the joints with epoxy resin and woven carbon cloth was practically the same as for the carbon frame. The bamboo rods, in the place of connection with the carbon were machined, so there were small shark teeth which guaranteed that the bamboo will not loose. Also it is important to have well dried bamboo, so it will shrink later minimally.
Step 12: Building the bamboo/carbon frame 4
After three years, I can write that the bamboo frame fulfilled all my expectations. The frame is excellent and still okay. Compared with the carbon frame it really does dampen vibrations better and the ride is more comfortable.
The connections of the bamboo rods with the carbon joints are still rigid without any problems. I know I can expect the bamboo to shrink or split sooner or later, but I hope that thanks to the used method of securing the mutual connection between the bamboo rods and carbon joints it should not loosen in the case of shrinking and the splitting of bamboo can be easily repaired.
I love riding this bike!