I notice that rakes made out of bamboo have curved tines (as shown below).
How can I permanently bend bamboo like there tines?
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In most commercial applications, the bamboo is treated with steam to soften it. You can also soften it by soaking in water, but it takes a lot longer. You can even apply heat to the bamboo, which softens it and turns the water contained in the bamboo to steam.
If a specific shape needs to be replicated, like those tines, the softened bamboo is put in a form until it cools and dries out. Steam treatment followed by a form is essentially the same as the process for bending wood.
3 Ways to Bend Bamboo, describes three ways that don't require a steam chamber.