I didn't read everybody comments, if I'm repeating what has been said, forgive me.
You didn't say what type of wood you are bending, how thick or what type of curve you are bending to.
To start off, figured wood is hard to bend without cracking, It's best to use straight grained wood. You also need to pay attention to wich way the grain is running.
Wood veneer, which is usally 1/42" thick, bends easy. Most times, just the moisture from yellow glue is all you need to bend a gentle curve.
If you are bending a tight curve you need to soften the wood by either soaking it in water, steaming it or heating it. I have bent cherry that is 1/8" thick on a 7" curve just by soaking in a tub of water. I won't try this with a open grain wood like red oak. But the bottom line is, not all woods can be bent all the time.
There is a write up in the article "Segmented Pen Blanks" about this type of pen blanks which may help you some