I built the panel for the lid out of two boards joined together. After planing a flat edge on each one I glued them together without using any clamps, just setting one on top of the other. If done right, this gives a nice tight seam with no worries of bowing the panel by using excess clamping pressure. After the glue has dried overnight I planed the faces flat and smooth making sure the inner side gets its final polishing.
Then I get groovy with the panel, running one around each side. This time I’m referencing the groove 1/4″ from the inner face so this groove and the groove in the frame will mate properly. Cutting the end-grain goes very well once you get past the initial rough surface.
To arrive at the proper length for the panel I measured the distance inside the frame in the long dimension then added 1/2″ . Since my grooves are 5/16″ deep this leaves a combined 1/8″ extra space for movement. That’s plenty since the panel won’t be expanding in length anyway. I measured the same for the panel width but only added an extra 3/8″ this time leaving a combined space of 1/4″ for expansion. Even though there are charts and formulas I always feel like I’m guessing at the amount to give for wood movement.
The plan called for a round-over on the top edge of the panel but I don’t own any moulding planes so I put a simple chamfer around the edge instead. I didn’t mark it off, simply did it by eye until it looked right. Sorry, I forgot to take a photo of this. Following a few test fits and tweaks I glued the laps together and left it overnight.