[BerntR]

I think you're looking at it the wrong way, Air.

70 degrees or whatever between the two forearms when you look down at them is OK.

But at impact - down the line - the right forearm should be on plane with the shaft* and the left wrist should be flat.

Now, if the left wrist is geometrically flat at impact, the plane of the left arm flying wedge (the plane defined by left arm and shaft*).

And if the right forearm is on the shaft* plane at impact. you will have a plane defined by the right forearm and the shaft* that is 90 degrees to the LAFW. At impact, the LFFW plane will be the same as the swing plane. So you have one inclined LFFW plane that "aims" down the target line. And one vertical RAFW that aims at right angles to the target line.

shaft* notates the sweet axis from hands to sweet spot. Close enough to shaft for most discussions.

Edit: The plane of the wedges are defined by the angles between left arm & shaft, respectively right forearm and shaft. If you look at those angles as lying on two different planes you should see a 90 degree difference between the two planes.