The RM manual states that only hard woods should be used . That was probably because back when that manual was written , the cave man never thought anyone would use flat segmented boards to make a bowl from so there would be no end grain sanding at all .
A flat one piece board or a laminated one has end grain to sand out on two sides and seeing as the cut out of the rings is never as clean on end grain it takes a lot more sanding .
This one took ten minutes of sanding after the rings were glued together .Of course no lathe tools were required. Sanding only .
I used one 22" long x 4 3/4" wide board of 40 to 50 year old cedar hydro pole that was given to me last week and added a little poplar for contrast .
It is 9" diameter .