Hex Tubes- The Basics
Hextubes are bamboo/carbon fiber composite tubes that are strong, stiff, lightweight, and relatively easy to construct with basic woodshop tools.
I’ve been making these things for a few years now, and I’ve figured out some techniques that seem to work pretty efficiently, but I am constantly tweaking and adjusting the process. Please check out the Semester bikes at the HERObike website- www.herobike.org
These are just a few of the bikes made using hextubes. I want to thank HERObike in Greensboro, Alabama and the Department of Design at the University of Kansas for their continued support.
Step 1: Harvest Your Bamboo
It's surprising how many places bamboo can grow in the US. But the kind of bamboo you need for hextubes grows mainly in the southeast. If you're lucky, you might know of a stand of "Giganticus" or even large diameter "Golden". Moso is the gold standard of big bamboo. You need bamboo that is 4"-6" in diameter.
The wall thickness should be at least 5mm. Cut it on the chop saw to lengths about 70cm
for bike tubes. Split it with a machete (or a sharpened piece of road sign) into pieces about 30mm wide. Dry these strips in the sun for 2-5 days.
Step 2: Calculating Strip Size
You can make hextubes in a variety of sizes, but for bikes, tubes are usually 35-45mm in diameter. I typically make a frame with internal lugs, so I need to calculate strip sizes based on the diameter of the lugs. This will be the inside diameter of my hextubes. According to the specs, a composite hextube with 4mm wall thickness that is designed to fit over a 28.6mm steel tube lug must be 39mm between the flats, and each strip should be 22.5 mm wide.
Step 3: Cut Your Strips
Plane your strips down on both sides. The back (inner) side doesn’t need to be perfectly flat, and you want to have the max wall thickness you can get. You need at least 3mm- this one’s about 4mm. I think it’s good practice to have all of the pieces for one tube to have the same nominal wall thickness.
Cut them into strips. Lots of ways to do this. I mark one edge and cut it carefully with a bandsaw. Then I set a tablesaw to cut widths. You need at least 20mm (like this pic) for bikes, but for bigger tubes, you need wider strips.
Each tube requires 6 strips...make a few extras, I guarantee you'll need them!
Step 4: Finish Strips
Then I use a 30 degree router bit to bevel the edges. I set this up on a router table, or use a simple jig to hold the bamboo. The router gives you a good clean gluing edge. Then I tape 6 of these strips together edge-to-edge with masking tape.
Step 5: Making a Composite Tube
The photo shows the bamboo "flat" as well as a length of carbon fiber sleeve and a piece of bicycle inner tube a little longer than the bamboo and tied off at one end with the valve on the other end. I glue these with epoxy, painting it on the seams of the bamboo as well as a generous coating on the carbon fiber. You don’t need to be too careful, but you need resin on all of the gluing surfaces. Then I roll it up and wrap plastic electrical tape around it to hold it together tight. Then attach the inner tube valve to a bike pump and carefully get about 30 lbs of air in the tube. Too much air will burst the tube. Let it sit overnight.
Step 6: Finish Your Tube
When the epoxy cures, remove tape and lightly block sand exterior surfaces. I've used a router template to cut strips for furniture or bike tubes that flair at the ends or bow in in the center. That's it. It seems a bit complicated at first, but surprisingly easy to do when you get into it. I've used hextubes to make bike frames, but also stools, tables, and even a tea cart. See the "Walmart Hack Bamboo Bike" for a simple 2-tube bike frame project!