I was fortunate to find some poplar boards wider than 16 inches to use for the three shelves and two spacers (top and bottom). They were cross cut and ripped to rough dimensions, then taken down to 1/2 inch thickness with the drum sander. The boards had significant cupping and a bit of twist so I used the #7 jointer plane to make them flat enough to be stable as they were fed through the drum sander.
Even after making then desired thickness and flat they cupped significantly and differently from day to day depending on temperature. This made fitting a challenge. With many projects the case joinery and construction can restrict that type of movement. In this case I was not totally confident that the structure could exert adequate pressure when and where needed. But I proceeded in hopes that it would work out.
Quarter-inch mortises (through and enclosed as required) were cut with router and edge guide. My initial test fitting was rather messed up. The labels did not seem to make sense. See images below. After some head scratching I realized that the labels were fine, but the middle shelf had been cut too short. Also, one set of mortises was not in proper location. Those were plugged and re-cut. It would not be a problem because they would still be covered by the mating pieces. I had enough extra material to cut, mill and fit a new center shelf. “Measure once, cut twice.” Or something like that.
A bevel up smoother was used on the top and bottom shelves to create bevels matching the curve of the outer circle. The middle shelf was symmetrical as the edge is parallel to the tangent of the circle. Rasps and sand paper were used to create the round overs on all edges.
One image below shows two shelves with early stages of finishing. I will create a later post with more details on the finishing processes I used.