I planed another .250" off the block, and opened the center hole to 4.5" (actually about .125" over that, off the machine - same as the last time). So far, it has been remarkably stable. One more of these operations, and I begin routing the pockets out between the spokes. This was a great camera shot that really brings out the grain. I can use it to begin plotting what three sections I want capture in the spoke landings.
