One of the hardest parts is getting a good mitered joint. This is worth practicing a few times first.
Method
Give yourself a lot of room for error. Cut poles so you have at least an 1″ to an 2″ on each side, just in case. Mitering should be incremental, not an all-in wager. You can use this really handy online tool to help you get the pattern right. Make sure you read the instructions below the tool though. Diameter 1 refers to the piece you are mitering, and diameter 2 refers to the tube you want to fit it too. Make sure you check the angles too. Keep in mind since bamboo isn’t perfectly round, this tool just helps as a general guide.
Pattern from mitering online tool.
Use your tungsten cutter, I find that trimming at a hard angle from the inside allows you to make smooth cuts (in first picture). Then I suggest slowly shortening the poles using sanding paper and a similar sized pole (below). This will create a nice fit with a lot of surface area for the glue.
Tip! If you over do it and cut something too short your in luck. Sure its not the best solution but it works well enough. Mix some epoxy and then add West System’s 403 microfibers or 404 High density filler to the mix. This allows you to rebuild a bit of the tubing and re-miter it.
Tip two! Remember the nodes on the bamboo are the weakest link (although they look the strongest). Read about bamboo issues here.
Long-armed protractor-like thing for checking your angles they sell a cheap flexible plastic one at Home Depot
Building A Bamboo Bike 
Posted by Paul Wujek on August 23, 2010 at 8:23 pm
To mitre my joints I took a small length of the correct diameter bamboo tube and wrapped the end with cardboard.
I would then extend the cardboard to have a tube of the proper diameter, and trim it with scissors until I had a shape that I could test in position.
Once the cardboard was cut to the appropriate shape I would then transfer the shape to the work piece for final shaping with the Dremel.
Posted by thomas on January 8, 2012 at 12:47 pm
I noticed on the bamboo bike studio site they say that they use “butted/cored construction” rather than mitreing. Can anyone give an overview of this technique and the advantages over mitred joins?
Posted by thomas on January 8, 2012 at 1:41 pm
Sorry for the double post but I seem to have answered my own question. http://www.laekhouse.com/blog/?p=949 details the process a bit at least.
Posted by Patrick on July 23, 2012 at 11:40 am
In woodworking, a mitered joint is a straight lined angular fitting between two abutting or intersecting members, whereas those involving more complex intersections, including those with curves, are known as a coped joint.
Do bike frame builders use the verb “cope”, or the noun “coping”?