The measurements are designed for a specific assembly pattern.  The side panels must be placed in-between the top and bottom with the top and bottom widths extending out the farthest and the side panels recessed and flush with the top and bottom.

The back panel is recessed in and flush with the top, bottom and side panels.

The doors are designed for the top and bottom panels to be recessed flush.

 The side panels should be recessed into the front.  This will minimized exposed edges when the box is closed.

The base stand is designed for the short sides to recessed flush into the longer sides.  The center support of the base is recessed an extra 1/4" to allow for a lip to keep the chuck box in place.

The legs of the base are rabbited together, but the cleats for the center support are simply screwed and glued.