schematic or design for original drop boards

[ebb]

Hi. Believe 338's were original too. But the three equally sized pieces are 3/4" solid mahogany with a fat spline-filled dado on the sliding edges.

Middle horizontal edges have a simple 1/2" lap for shedding water.

The splines are 5/16" wide and are 3/4" deep. These glued-in splines must have helped keep the solid boards from warping, kept the boards from splitting, and long grain made a smoother edge for sliding. It's a nice simple trick that's lasted for decades.