There have various instructions on how to do this bending, but the method I used this time was steam. After thinning the bamboo to about 3-4 mm, I held the bamboo over my steam iron for a couple of minutes until I could bend it. There was some cracking on the back, but eventually that got carved away.
We used two different kinds of bamboo, black bamboo and giant timber bamboo. The black bamboo was easier to carve, but more brittle. It split more easily and you had to be very careful when shaping it. The green bamboo was harder to carve, but more forgiving of splits and mistakes.
I think it went very well and the students this time got to take home a usable chashaku. The final assignment from the workshop, is that everyone had to name their chashaku.