Saw has two different meanings... one is the past tense of the verb "to see" and the other one is a noun meaning a tool. However that noun became the verb to describe the action of the tool.
Robert is correct in saying "Did you saw" is grammatically incorrect. However, "Did you saw it?" is correct as "saw" can only mean one thing - the action of sawing. Because of the rules of English grammar, the sentence is not ambiguous. It would be clearer if it had been, "Did you saw the piece of wood". However in other cases the sentence is ambiguous. For example, "The Queen threw a ball". Did you really throw a ball (a toy) or a party?. Therefore only the context can infer the correct meaning. But if you know that the Queen never touches the toy ball, you can deduce it must be a party. This is one of the reason that computers of today cannot "understand" the meaning of sentences. It would take enormous amounts of memory to store context information and experience that today's computer are not capable of having.