The manufacturer must put all the warnings possible in their instructions for all sorts of potential liability issues. Why would it be dangerous to use just one blade? ..... for the reason I suggested. The blades have different outfacing bevel teeth, one blade to the right, one to the left. To cut with a single blade with outfacing bevels "might" have a tendency to favor that side in feeding and throw the work sideways to the "no bevel" side. This could result in a kickback, hence the danger. Best to contact Freud if this issue really stumps you.
OR if you are brave enough, just mount up one blade, set the fence and see what happens.... Don't say I "advised" you to do this, it was a suggestion made in jest. I'm sure you have other blades to use if you need to make a single width kerf.
I did contact Freud, and posted their reply above. I had already planned to risk my life and perform that dangerous single blade test. I chose not to announce it. I ran the tests yesterday, and learned a few things:
* As we know, the carbide blade tips overlap each other in a two-blade dado pack, which is the minimum recommended use of the Freud SD208 dado set. The overlap occurs between the two blades. One function of the overlap is to allow a proper cut even if a shim is between the blades.
* Observe that the carbide tips on inner blade (closest to the motor) stick out sideways from the blade plate (body), toward the arbor nut. The carbide tips on the outer blade stick out toward the motor.
* If you try to mount the outer blade on the inner part of the arbor, closest to the motor, the carbide tips will stick out toward the motor and the blade will not turn because of interference between parts in the saw itself and those protruding carbide tips. This means that you cannot make cuts with the outer blade only or with the inner and outer blades reversed in position.
* The only tests I could run were with the normal two-blade dado stack and a cut with the inner blade only. Freud has stated that running the inner blade only is dangerous.
In the interest of science, I ran the test anyway. I will post photos of the test setup in this post, and photos of the results in the next post. Here are my photos of the test setup:
* Two Blade Setup 1: This is a normal two blade dado stack in the saw.
* Two Blade Setup 2: This photo shows the angled bevels and flat rakers in the two blade dado stack. Observe how the bevels alternate. (If I had to do it again, I would pay better attention to the bevels and rakers, so that they alternate, instead of bevel, bevel, raker, raker as shown in the photo.) Also note how the carbide tips on the outer (right) blade protrude toward the left. They stick out far enough to bump into the saw parts to the left of the blade, preventing the outer blade from turning at all if mounted alone or in a "reversed stack."
* One Blade Setup 1: This is the inner blade alone. WARNING
: Freud says that this is dangerous!!
* One Blade Setup 2: You can see the alternating bevel and raker carbide tips on this inner blade alone. The bevels point in only one direction.