Making holes in Bamboo

I’ve used the masking tape method to drill holes up to 1-5/8″ in dried culms using Forstner bits. Just make sure you use a decent quality tape with good adhesion (not masking tape for painting, which is less sticky).
I prefer Forstner bits because they slice through the fibers at the edge first and that also helps minimize fraying. I’ve even used these bits to cut a semicircular piece off the end of a large culm so that it matches the curve of another piece I’m joining it to. You just need to be careful in aligning the piece on your drill press table, and clamp it firmly and level. It helps if it’s an end that has a wooden plug glued in as described in my other post `A couple of bamboo joint techniques’ in the thread `Bamboo joints’. The little fraying I got with this drilling was easily cleaned up with a razor blade. The only thing to be aware of is that the glue you use to glue the plug in with can also cause a residue to build up on the outer circumference of the bit, so it may have to be cleaned off frequently with solvent if you’re drilling several holes.
If I’m working with really big culms — like 6″ in diameter — and I want to make really big holes I do the following. [I use this technique, for example, when making big bamboo water spouts for gardens.] First, I put down tape in an approximate circular shape that matches the size of the hole I want to make, and then mark it as best as I can in pencil. Then I drill a 1/2″ hole inside the circle, as an entry point for my sabre saw. I use a long blade and go slowly, cutting all around the shape I’ve marked, but keeping the opening a little smaller than what I’ll need. Once the hole is cut out, I put one of those little 1-1/2″ diameter sanding drums on my radial arm saw accessory shaft and use the drum to clean up all around the hole. I’ll just keep sanding away all around the edge, and doing test fitting, until the piece I want to insert fits right.