How would I create a buzz saw trap that moved from the lines it was placed to the ending area, then return to its start and begin again. A diagram:

B
--------------------
^S ^E

B: Buzzsaw

S: Start E: End

How would I make the buzzsaw move from where it appears at the start to the end of its path, but not go any farther?

then, how would i have it move back to its orginal location before starting again?

Thanks in advance

-_Rein_-