- Always use bamboo that's dry. Moisture keeps bamboo from setting after it's heated. Semi-dry bamboo will release moisture from the ends when bending it, which is usually a sign that it's being heated enough. Even days with high humidity can have an effect on how well bamboo retains its shape after molding.
- It's easy to burn bamboo on a bending mold. Once the jig is warmed up or has been in use long enough, it only takes a minute or two to heat the bamboo enough to shape it.
- As a basic rule, bend bamboo with the vascular bundles on the outside. When bending strips with the skin/vascular bundles on the inside, bend the strip more slowly, allowing the heat to soften the strip as you bend it, otherwise it could break (especially for thicker strips).
- After the strip is molded, take it off the mold by hammering out the wedges. Bamboo that is still hot won't retain it's shape, so it's important either to hold the bamboo with gloved hands, or use another non-heated mold to keep it bent until it's cooled. At school we place the strips in tin containers roughly the same circumference as the final rim (see picture).
- It's best to bend a strip more tightly (at a smaller diameter) than the curve it will be used for later. It's easier to unbend a strip without breaking than bend it more tightly after it was heated.
The bending mold we use at school is a rather complex piece of equipment that had cost the equivalent of several hundred dollars to have specially made. It's useful on an industrial scale, but remember that you don't need as fancy a device when making your own crafts at home. I've been successful bending 2.5 mm thick strips at home buy using a metal cake tin I bought at a 100-yen (1 dollar) store, screw-on clamps, and my kitchen stove. It takes a little longer but works just as well. Also, keep in mind that Japanese craftsmen long ago and some even today didn't/don't even use a round bending mold like this to make rims; they just rubbed the bamboo across their knees to soften and bend the bamboo enough to make a circle. Cutting the strip extra long before bending makes this method much easier.I think that's about it. The process has become so natural to me by now that I can't think of anything else that might be worth mentioning. If you have any questions please leave a comment.