Here's my thought

[wtnhighlander]

Since Colin mentioned using a jointer to reduce thickness, I would point out that doing so, while certainly making the cut face FLAT, may introduce a taper due to uneven downward pressure across tbe cut. The thickness planer would then be used to mill the opposite face to make the two face parallel.

Try it with a nice soft 2x4. Exagerate by passing the same face across the jointer repeatedly, it the same direction. If the machine is well tuned, and your technique is well developed, you may be able to keep the faces parallel, but my experience has been otherwise.