Prepare 2 pieces of poplar ¾” x 2 ½” x 16 ¼” [19mm x 63.5mm x 412.7mm] for the stiles.
For the back rail you will need a piece of poplar 1/2" thick [12.7mm] x 2 3/8" [60.32mm] wide.
For the balance rail, you will need a piece of hard wood (red oak, white oak, maple, etc.) 3/4" [19mm] thick and 2 1/4" [57mm] wide.
Please Note: The length of the balance rail and back rail must be identical. This length is equal to the actual width of your keyboard plus 1/4".
For the time being, make both the balance rail and back rail 29" [736mm] long.
Take the two pieces of poplar for the stiles and place them next to one another with their front edges (a 2 ½” [63.5mm] edge) perfectly flush.
Clamp them together, long edge to long edge. Measure 5 3/64” [128.2mm] from the front edge and draw a line across both pieces at this point.
From this line, measure 2 ¼” [57mm] and draw another line across both pieces. These two lines define the dado that will be cut into these
pieces to accept the balance rail.
Without removing the clamp, measure 2 3/8” [60.3mm] from the rear end of the stiles and draw a line across both pieces. This defines the
width of the rabbet at the rear of the stiles to accept the back rail.