I have built this carbon composite MTB frame four years ago using simple building method which is described in this Instructable. Of course, this method is not suitable for mass production, but if you plan to build just one or two frames for yourself, it is sufficient and you can build your own frame of a high quality. The feeling of riding a self-made frame is great!
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
1. Frame jig - it is used to hold all parts in their exact position. I have built the frame jig from scrap wooden rods and some lathed parts and connected with screws. You can also build e.g. adjustable aluminum jig, where you can make the frame geometry according your needs. As a template of a frame dimensions for construction of a jig, I have used my bike frame that I rode before. The completed jig was stiff enough and guaranteed the position and the alignment of the metal parts during the construction of the foam core.
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
After I have built the frame jig and all metal parts were secured in the jig, I began to make the frame 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 adding all of the polystyrene rods I have sanded all of the added small parts in the places of rods connection areas to achieve soft shapes. After that I have wrapped these junctions with one light layer of fiberglass. After the curing of the epoxy resin, I have softly sanded the whole surface.
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
I was a little bit afraid before I have added the first layer because of lack of experience. I only had theoretical and little practical knowledge of how to do it, but by following the instructions on how to mix the epoxy and how to wet out the carbon cloth it went okay. I have wetted out the pieces of carbon and I have added the first layer on the foam core. I have tried to cut as large pieces of carbon as possible. For each tube, I have used one big piece with overlapping about 1 cm.
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
In this picture, you can see the frame after the first layer was added and the electrical tape was removed. It began to look like a real bike frame. Approximately four-five hours after first layer had been done, I removed electrical tape lightly and I added another layer, and again, I wrapped it over with the tape. I have tried to make as many layers during the day as possible, because after it fully cured overnight I had to softly sand the surface for the next layer. Before the last layer I have bonded the rear brake bosses and have reinforced them with few carbon layers.
Step 6: Laminating 3
During the construction, I have combined the layers diagonally and cross-wise. On the top and down tubes and seat tube, there are 9 layers; on the chain stay and seat stay there are 11 layers. The high stress areas were covered with additional 6-8 layers. I have added two more layers as I initially planned just for the safety, but if I built this frame again, probably I would not add them again. I have sanded the surface carefully before the last layer.
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
After removal of the fully cured frame from the jig, I have cut the excess carbon and I have sanded the entire surface. Also I have bonded the cable stops and then I have sandblasted all the visible aluminum parts. I have added a few layers of wet epoxy, with sanding between each layer. The sanding is the worst part of building the frame, don't do it in your living room... The whole surface was polishing for a better look. But it is better to spray some quality clear varnish over the surface.
Step 8: Finished Bike
This is the finished bike with my homemade carbon frame.
Step 9: Building the Bamboo/carbon Frame
I have seen many amazing constructions made of bamboo and I have always wondered why such light, strong, stiff and elastic material is not widespread used for building of bicycle frames, although such frames were built already hundred years ago. Since I have finished my carbon frame, I was thinking about using bamboo for my second frame. Later on, I have found an article describing a bamboo frame Craig Calfee built for himself a few years ago. At that moment I was fully determined to build it too.
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
When I have built this bamboo frame, I was interested in how would it differ from my carbon frame. Above all I have expected that thanks to the unique properties of bamboo, as a natural composite, the frame would be more able to absorb road shocks and the ride would be more comfortable.
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!