The selection and shaping of a particular piece of timber is more involved than it may appear.
I am writing an article on the use of Australian timbers which will go into the selection and shaping of timber with a particular grain pattern or growth ring orientation.
To cut a long story short:
If the growth rings are parallel or at an angle to the edges of the Bokuto (normally considered the ideal) then the line of those rings must go the length of the Bokuto if possible, from tip to Tsuka. Then the grain looking side on to the blade is not as important, although I am always looking for a piece that is correct both ways (I have just done an Aikido bokken like this).
If the growth rings are horizontal to the sides of the Bokuto, I don't discount it, as I an doing my homework on laminated engineering timber, which is sometimes oriented this way. In this cases it is critical that the grain of the timber when the Bokuto is looked at side on should follow the whole length, from Kissake to Tsuka.
In cases where I have tried this, I have done the current breaks, Coconut, 25mm Tas Oak dowel and 20mm sandstone paving slabs, and have not managed to break a Bokuto.
Maybe I will step up the testing to see what the limits are, but I want a practical test, not 'break the Bokken', because anything can be broken with enough power and the immovable object
Sorry, it's easier to show that explain, maybe a sketch would be better.
I don't have a video of me doing the whole process from plank to finished item, I might think about it, but I would rather prove that I am on the right track first, to explain from a position of competence.
All the best,
ps. to the moderators,
I don't know if this is still the correct area of the Forum for this discussion, if it's not, please feel free to let me know.