Your particular model is a stacking set that apparently has a 1/2" max width. To use you simply place the chipper sets the three twin blade pieces between the two edge cutters. This will give you your dado.
Its actually fairly simple to use but a pain to adjust, the way to make it smaller or larger is add or remove chippers. For your application you will need to set it for two passes. I can't imagine that set is very acurate, due to it not having shims at all the Forest set and Harbor freight seam to be the best rated models, frued is somewhere in the mix.
Unfortunatly Craftsman is not very well rated.
I my self use a really old wobble dado, or my router.
What is exactly the problem you are having?
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Jeremy
"I am become death, the destroyer of worlds" July 16, 1945 Robert Oppenheimer
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