After gluing up the four sides, my next step was to rout in the puzzle pieces.
I used three combination squares referenced off of each edge to lay out a grid, which represented the size and location of the puzzle pieces.
Pencil can be difficult to see on black walnut, but I found that roughing up the planed surface with 120-grit sandpaper made the lines easier to see.
I routed the jigsaw puzzle design with a 1/8″ spiral bit, doing one line at a time.
It was very gratifying to see one surface completed.
Next, I rolled the cube and continued routing puzzle pieces into the other faces.