Tim,
When you read George's (texatdurango) tutorial you'll learn that to have the rings aligned is a matter of marking the blank properly and using hold-downs and stops to keep the blank in the proper location for each cut.
http://www.georgeandsirik.com/knot-tutorial.html
Simply, Suppose I cut 1/8" at 45-degrees from a 1" X 1" X 6" blank.
Then, glue in a slice of wood 1/16" thick.
When the second cut is made with an 1/8" thick blade, part of the slice disappears and maintaining alignment becomes a matter of luck rather than controlled accuracy.
That's where the slice thickness == blade thickness comes in.
If you glue in an 1/8" thick slice, parity is maintained and you can continue.
Now, rotate the blank 180-degrees to make the second 45-degree cut, the center of the cut must go through the center of the first glued-in slice.
This is how they'll intersect. Otherwise, the rings of the knot won't line up.
Each following ring uses the last as it's foundation, so you have to maintain a constant size to maintain alignment.
I hope that's clear and correct.
Gary