There is surprisingly little on the web about how to choose bamboo species. I have done a fair amount of research and have figured out a few things. Note before buying your bamboo make sure you look at all the other directions on this page. Each pole will have to serve a specific purpose and as such will need to meet certain specifications (diameters, length between nodes etc).
Local Sourcing & Bamboo in General – A few comments.
Finding it. Sure it can be hard. I found mine by contacting the local chapter of the American Bamboo Society.
It is important that you choose older bamboo poles. Younger poles are not fully developed structurally. Also some poles are born to split, its better to have a pole that his demonstrated its worthiness for your bike. You can generally tell the older poles by looking for weathering, if it looks like a polished pretty thing, its probably very young.
Second, the poles will have the thickest walls near the base of the pole. These thick-walled pieces would be a good choice for your seat tube since it bears a lot of weight. Keep in mind that the rear triangle bears a lot of the brunt too. Choose your pole carefully.
Third, the nodes on the pole are the weakest point. The individual fibers traverse to the other side of the poles. This is apparently the weakest link, so try to avoid using them for structural components.
Fourth, respect the bamboo. Each piece is different. Try to figure out how best to use bends, thick walls, etc to better suit the build characteristics of your bike.
Fifth, (courtesy of Fox.Gao) “One of the reason for bamboo poles split is the time to cut the bamboo poles, the best time to cut the bamboo poles is in Autumn or Winter, not cut the bamboo poles in Spring or Summer—–that is the rain season and the water contents of the poles is too high. Another issue for choosing the bamboo poles is the altitude of bamboo growing, more high altitude means the bamboo grow more slow and more firm.” This advise makes sense. I cut my poles after a very rainy summer in MA.
Finally, you might consider doing a chemical treatment of your bamboo to reduce splitting, and to prevent mold/pest formation. Most of the retail purchased bamboo will have undergone a chemical treatment, so you might do the same. For more detail on this go to the ‘chemical preservation’ section below.
Probably the most common bamboo is Phyllostachys or taiwan bamboo:
This is the type that I cut from a generous fellows backyard a few months ago. Phyllostachys seems prone to splitting, I lost about 3/4 of my poles during the 3 month drying process, oddly enough the longest poles seemed more prone to splitting. I did learn however that heat treating the poles when green might help avoid this problem. I will get into this later. The poles that did not split seemed adequately stiff and relatively light compared to the phyllostachys negra (black bamboo) that I ended up going with. In the end I choose to purchase some better quality poles.
Black bamboo while terribly sexy appears to be prone to splitting also, at least according to bamboo forum folks. The poles that do make it however appear to have thick walls and come in a convenient variety of diameters. In the end this is the only type of bamboo that I found that could meet my diameter requirements. I ordered my poles from bamboofencer.com although you can also get them from bamboohardwoods.com. It’s a bit expensive but the poles are very nice. I ordered three 8 foot, 1 and 1/2″ diameter for the main triangle and three 8 foot 1″-1 1/4″ poles for the rear triangle. Having extra was key. I would recommend buying one additional 1″-1 1/4″ diameter pole (make 4 total) to make sure you have enough to work with (smaller poles have a strong taper and thus don’t give you as much room for error).
The bamboo of choice apparently, according to one of my bamboo friends, is tonkin. It is strong light and less prone to splitting…. apparently. This is the type of pole commonly used for bamboo fly rods. Unfortunately I couldn’t get it in the proper diameters, but I just found that bamboohardwoods.com has it.
Heat treatment is really frikin important. Apparently it hardens the sugars inside of the canes, kills unwanted guests, and helps remove some moisture. Also, as pointed out by a reader “andreas”, the bamboo poles diameter changes as it gets dried by heat (~3%). This can be problematic if non-heat-treated bikes have prolonged exposure to heat (left in the sun over hot pavement etc). Apparently this shrink can be severe enough to weaken the bond between joints and pole. When it comes to heat treatment, I just do it.
I have read many times that you should use a regular propane torch, starting at the base of the pole work your way to the top. The method to temper the bamboo is to heat it when it is green, with a propane torch, moving the flame up and down the surface of the culm until it changes from shades of green to tan and if desired, to darker shades of brown. I suggest a light browning for the first step. Then you have to dry the stuff, for real. The torch only partially removes the water content. Alternatively if you buy the stuff through a good supplier your poles are likely pretreated and dried. Keep in mind that some of the poles bought from abroad will have been chemically treated, and we all know that chemical regulations in developing countries are lax at best. So be careful and use a proper respirator. Anyways, in this case I would just heat-treat the individual poles that you buy before you use them. Some types of bamboo might react poorly to heat treatment, so keep that in mind if you are having trouble.
Locally sourced poles however still need to be adequately dried. People on “bamboo forum” have a number of views, but I think stacking them vertically for about 3 months, yes 3 months, does the trick. To avoid getting mold build up make sure that they get adequate air circulation. Also keep them out of direct sun. If you don’t dry them properly (and heat treating them with a blow torch doesn’t count) you are likely to have more splitting problems. Some poles just seem destined to crack, better to find that out before they are part of your bike.
Pole Diameter and Wall Thickness
So far there is only one comprehensive study of bamboo strength and heat treatment. http://www.powerfibers.com/BAMBOO_IN_THE_LABORATORY.pdf. Here are some of the important findings.
Although I haven’t studied physics in a while here is my simplistic take. Your most important poles, requiring the greatest stiffness should have 3mm walls or more. The seat tube and down tube on my bike both have 3mm walls. Your smaller poles (seat stays, chain stays) should be as thick as possible. I believe mine are around 2mm.
One of the big surprises here was the lack of breaking strength improvement. It does however point to the faults of over heating your poles. Breaking strength declines rapidly after the internal temperature reaches 200 degrees C. The ability to bend the poles increases however. Again we see a rapid failure after 200 degrees C.
I have also read about smoking your bamboo poles. Apparently you can use scrap bamboo or cracked poles to smoke others. Apparently the tar from the burning bamboo helps to protect the bamboo from mold, pests etc and some site even claimed that it helped avoid cracking… can’t verify that. Some types of bamboo might react poorly to heat treatment, so keep that in mind if you are having trouble.
Although I haven’t tried it this is what I’m thinking. I was planning (didn’t get around to it) to use my father’s old barrel smoker. Soak the bamboo pieces in water and then throw it in.
If you don’t have a smoker you might try to do something like this. You could add a right angle to the air conditioning tube and laying the poles in there.
They use a borax mix to help create poles that are inhospitable to bug, molds etc. This process should also reduce splitting. Many of the higher quality poles you can buy online go through a similar process.
For more info on professional grade bamboo preservation go to: http://www.bambooman.com.au/bambootreatment/ebf.php
No I’m not getting paid to say this. I just think this is the best bet (until I hear otherwise).
Zack Jiang at Stalk Bikes has opened an ebay store to sell bamboo bike building materials. So, he knows what he’s doing because hell he does it for a living. So support the creative guys of the world and buy your building materials here.
“Bamboo Habitat now offers bamboo selected specifically for building bikes. This bamboo has been selected by going through the bamboo groves and choosing the oldest bamboos that have the proper diameters. By selecting the oldest bamboo, we are getting the maximum fiber content, which assures that the bamboo is very strong. The bamboo is then power washed and then kiln dried. The types of bamboo we have are Black Bamboo, Madake Bamboo and Blue Henon Bamboo. Of the three, the Henon Bamboo is the strongest, but the Black Bamboo and Madake are also exceptionally strong.”
www.bamboocraft.net/ Tons of topics, more detail than you need
www.bamboohardwoods.com Supplier of bamboo poles: Tonkin, Black, Moso
www.bamboofencer.com/ Supplier of bamboo poles: Tonkin, Black, Phyllostachys
http://www.americanbamboo.org/ All kinds of bamboo info
http://www.bamboocraft.net/forums/archive/index.php/f-111.html More info on bamboo treatments
Although completely unrelated. Check out my family’s farm. The site is just up… here it is.