How did Ruben invent the saw?

How did Lu Ban invent the saw?

Lu Ban was a skillful craftsman from the state of Lu during the Spring and Autumn Period. According to legend, he once undertook to build a large palace, need to use a lot of wood, he told his disciples to go up the mountain to cut down the big trees. At that time, there was no saw, with an axe, could not cut many trees a day, the supply of wood is not, he was very anxious, so he went up the mountain to see. The mountain was very steep, and when he was climbing the mountain, one of his hands was pulling on the silk thatch grass, and all of a sudden he pulled his fingertips through, and blood flowed out. Lu Ban was very surprised, a small grass why so powerful? For a moment he could not think of a reason. On the way home, he picked a silk grass, take home to study. He looked right and left, and found that there are a lot of small teeth on both sides of thatched grass, these small teeth are very sharp, with a finger to pull, and cut through a mouth. This reminds Lu Ban, he thought, if like silk thatched grass, into a toothy iron, not to saw the tree? So, he and the blacksmith together to try to make a piece of iron with teeth, take to saw the tree, and really succeeded.