Turned over the 40" blank this past Sunday with the help of a friend to evaluate the flatness of the back...well it isn't!
Will make a tool 16" in diameter of dental stone to flatten out the back.
The material is extremely soft! It should take maybe 30 minutes of grinding with #80 grit to flatten out the back. That is my guess.
Also took my bevelling stone, dry, and tried to take off the sharpness on the edge of parts of the back of the blank. Again the material is super soft. I will take an ordinary sander and bevel out the rim of the back and front with #120 sandpaper.
It should work without causing chips and reasonably fast.
Dan Kahraman