DISCLAIMER: If you try this, it's your fault if it breaks and you get hurt. Frame failures are no fun, and if you build this and your frame fails, it is very possible you will get hurt. Don't blame me.
The basic process will be:
1. Get materials!
2. Design the frame
3. Heat treat the bamboo
4. miter the tubes; the head tube and the bb shell will be metal parts that fit inside bamboo sheaths.
5. Tack it all together
6. Reinforce the joints
7. Build up a bike
Step 1: Materials and Tools
- bamboo, of the appropriate sizes. I got mine from OSH. They had " 1" Bamboo ", which in reality ranged from .75" to 1.25" in diameter, and " 1.5" Bamboo ", which in reality ranged from 1.25" to 1.875". I used .875" for the rear triangle and 1.5"-1.75" for the front triangle. It's definitely strong enough.
- hemp fiber, or fiberglass, or carbon fiber. I used hemp fiber from hemptraders.com. Fiberglass is cheap and available at OSH. You can get carbon fiber ( and fiberglass, too) at fiberglast.com .
- epoxy resin and hardener. 10 minute pot life worked well. I got mine from West Marine, and it's available at fiberglast.com too.
- 5-minute epoxy. Or 30-minute, or 2-hour, it really depends on how patient you are. I got them from OSH.
- a head tube and a lugless bottom bracket shell. I got mine from novacycles.com .
- dropouts. I got mine from ebikestop .
- expanding foam. I'm not sure if it is needed, but Brano Meres seems to think foam does good things, so I put some in the rear triangle. It helped keep the dropouts in their place when it was all getting tacked together. It's light and cheap, and I got it at OSH.
Tools you'll need:
- a propane torch, or a heat gun. This isn't necessary if you can breathe fire. It's for heat treating the bamboo. Mine is from OSH.
- a hacksaw or a coping saw. This is for mitering the bamboo, and for cutting the tube to length. Mine is from Home Depot, I think. You probably have one already, though.
- if you have a drill press, I hear you can get an attachment that holds a tube at an angle so you can miter quickly and accurately. thavinator posted this link in the comments which points you toward where you can buy them.
- a half-round wood rasp. This is for mitering the bamboo. Got it from OSH.
- tubemiter.exe . Invaluable when mitering. Mitering tubes. Not so useful for mitering other things.
- a Dremel. Useful for everything. I bummed one off a friend, but I was almost done with the frame at that point. This would have made things go much faster.
- disposable gloves. Epoxy is bad for you, don't touch it. Costco sells these in bulk. Your local drug store will carry them too.
- a mask; epoxy and sawdust and the like is bad for you. Don't inhale it. OSH.
- a jig. I got aluminum from OSH and built the almost jig by dr welby . Well, you technically don't need one, but I found it to be very useful. You'll also need clamps if you use a jig.
- calipers are nice to have. I "borrowed" mine from my school's robotics lab. Harbor Freight carries them cheap, though. Measuring tape is also important.
- a protractor is important to have. Angles are important to get right.
- a Sharpie, or something else that marks up just about anything.
- trash bags; they are useful for making the joints.
- a camera, so you can document your work.
You'll also need bike components. I bummed around and got some free, and bought some for cheap. Total cost of the entire bike: about $300.
Step 2: Design!
I don't actually know much about frame design. I did a little bit of Googling, a lot of looking at pictures of bikes, and a bunch of poring over the geometry charts published by bike companies. Then I used SolidWorks to check for clearance. You don't want to finish your bike to find that your pedals almost scrape the ground, or, worse yet, hit your rear triangle!
I "tested" my bamboo for strength by stacking bricks on it, sitting on the bricks, and then leaning to one side. It was so rigorous. My bamboo withstood about 300 ft-lbs of torque.
I found a picture online that has the names of the tubes of a bike frame. It may be useful to you.
Step 3: BB Shell, Heat Treating
Heat treat your bamboo first, as there is a little shrinkage that happens when you heat-treat. I learned this the hard way. When heat-treating, I found it easiest to have the flame be very small and be very patient. Heat treating strengthens the bamboo by caramelizing the sugars inside it, bonding the fibers closer together. It also looks nice.
Step 4: Mitering
The seat tube is mitered to the seat tube at 90 degrees. Print out a template from tubemiter.exe, cut it out, tape it onto the tube, and go to town! First, I Sharpied in the line so that I could see the edge better. Then, I cut longitudinal slots down to the line, so that the bamboo would chip off as I sawed along the line. Then, I sawed along the line, and I finished with rasp work. After testing it against the actual piece I was mitering to, I did some more rasp work. And then tested again, and then some more rasp work. And so on, until I achieved a good fit. It doesn't have to be super tight, since you are tacking the two together with epoxy and not welding it, but it can't be *too* bad of a fit.
For the down tube and the top tube you will have to miter both ends, and they both have to be straight. The down tube will also have to be mitered to two tubes. My best advice is to be patient and careful. Use your protractor to check if your angles are the same in real life and in your design.
For the seat stays I used this calculator instead to make templates for the offset miters.
The bridges are very small, so they are hard to miter. I included pictures of how I did it.
Step 5: Tacking
For the front triangle, I first tacked the seat tube to the BB shell.
Then I tacked the head tube to the down tube.
Then I attached the seat tube and BB shell to the upright part of the jig, and tacked the down tube/head tube assembly to the BB shell/seat tube assembly.
Then the top tube was slid in and tacked. For this, I actually had the front triangle (actually a front V at this point) lying flat on the table.
For the rear triangle, I filled the tubes with expanding foam first. I capped the ends with tape to hopefully force the foam to expand inwards. The seat tube was replaced on the jig upright, and the dropouts were bolted to the dummy axle. I put the rear triangle tubes into place, using the dropouts to poke holes in the foam, which held everything in place while the glue dried.
Tacking is the best, it's not very messy and your frame looks almost rideable! Don't try riding it, though, you'll just hurt yourself and your frame will be in pieces again.
Step 6: Reinforcing the Joints
Masking comes first. If you haven't spread newspaper or cardboard all over your workspace yet, do so now. Use several layers of newspaper - this stuff soaks pretty well. Also, mask off the parts of your frame you don't want to have to scrape epoxy off of afterward.
If you've got vacuum bagging equipment, use that instead of this method I'm about to describe.
1. Cut up some strips of polyethylene (trash bags) and keep them handy.
2. Then get your reinforcement of choice (I chose hemp fiber) and break it into manageable chunks.
3. Mix your epoxy resin and hardener according to the instructions.
4. Soak the reinforcement in the epoxy, squeeze out excess resin, and plop it on your joint. Wrap it around and reinforce what needs to be reinforced.
5. Take the polyethylene strips and wrap them tightly around your reinforcement, so that you can squeeze out more excess resin. This will also help keep the surface fairly uniform.
6. Wait. Before the resin sets, but after it's no longer very sticky, take off the polyethylene.
8. Repeat 1-7 until you are satisfied with the amount of material reinforcing your joints.
Step 7: Build up the bike!
The rest is the same as a normal bike.