You should have both a riving knife and an outfeed table for your saw. But I doubt very much if either have anything to do with what's happening. As has been stated, it's the internal stresses of the board being released that's causing the problem.
Thanks for all the lessons! I agree it's probably the wood, after cutting a couple pices developed a slight curve, not enough to cause any major problems, it will straighten out easy enough, I can move it easily by hand.
I didn't see anyone as or note about weather or not your knife and blade are aligned to one another ? It could be possible that the riving Knife is off just enough that when the material is being pushed thru the blade that it might be pulling the material away from the fence at the back end of the Riving Knife thu causing you the troubles your experiencing. again just something else you may want to check.
