Even if the directional markings were worn off or if you had either a left-tilt or right-tilt saw-- They all go with the rotation of your arbor... (more details below)
Look at the teeth. The cutting edge of the teeth and the hook of those teeth... The cutting edge faces into the direction of cut. There is a left and right outside blade. It does matter. The outside blades of the dado face the same direction as each other, with the teeth facing into the direction of the cut and the bat-ears (the highest point of the tip is all leaned out to one side) to the outsides of the stack. The flat topped chipper blades also lead with their cutting edges.
If you have the outside blades facing into the direction of cut, but have the blades in the wrong sides of the stack (bat-ears towards the inside), they will cut, but 2 thiings will happen that will degrade the cut. Since the highest part of the cut is towards the inside of the cut, the sides of the groove will not have as high a quality cut to it. You may even see "steps" down one side of the groove. Second is that the stack will want to wander fractionally as cuts, so if there is any backlash in your arbor, the cut will not be as straight as it could be. That is why Frued uses bat-eared dado stacks. Those bat-ears to the outside do help on saws that may have a bit of arbor bearing backlash.
If you turn any of those around and mistakenly use them opposite the direction of cut, it ends up beating the wood to death and dulling your blades... possibly even in breaking the carbide teeth tips.
"Don't worry, I saw this work in a cartoon once."
"Usually learning skills and tooling involves a progression of logical steps."
Last edited by MAFoElffen; 04-03-2014 at 06:07 PM.