: Greg, In which of these two axes do I want the vertical grain?

Radby,

You want clear (knot-free) vertical grain lumber, aka quartersawn, If you place the board down on its wide surface (face), the grain should run from one end of the board to the other and look like pinstripes. The end grain should be vertical. Ideally the grain on the face will run straight down the board from end to end. If the grain runs across the face diagonally and exits at the side (run-out) then breakage is likely and the board should be rejected (especially if the runout occurs near the loom or roots of the blades). Most lumber you see at the home improvement stores is flatsawn (grain looks the flame patterns common to plywood). If you search through the stacks you can get lucky, I stay away from the 2 X 4's and look at 2 X 6's or larger. 4 X 4's can also be a good choice. Vertical grain tends to be stiffer, stronger and more stable (less likely to warp or cup) than flatsawn.

My advice is to visit a "real" lumberyard, especially if the boards are stacked on edge, so that you can easily see the grain orientation. If you can't find good solid lumber, you can laminate smaller pieces together.

Greg Stamer