Cross-grain panels. What to fix and what floats?

[Deadeye]

I understand that wood expands/contracts across the grain rather than lengthways.
I'm building a chest and the panels in the side frames will float on 3 sides because of this.
However the lid design is three long boards as a panel and then two "capping" end pieces running perpendicular.

I was going to glue the three long boards into a single panel and then cut tenons to slot into the capping pieces. Is that the right thing to do? I'm worried that the lid may cup if I glue the tenons in?

 

[Sheffield Tony]

"Breadboard ends" is what you need to look up. The ends are M&T, but with the mortices elongated except for the centre one to allow movement. Only glue in the middle, pegs through slotted holes in the outer tenons.

 

[MikeG.]

Deadeye describes traditional breadboard ends as used in a table. I guess that they would be done that way 90+% of the time. However, with a chest lid, it may be more useful to have the out "frame" fixed, and have the expansion/ contraction happening at the inner board. This would allow hinges and catches to work all the time. The outer part of the outer boards would be glued into the breadboard ends, and the centre board would be undersized in width (with half laps or T&G). The resulting gaps would be enough to allow for maximum expansion in winter, and would be quite open in summer. With, say, a bead & butt joint, this wouldn't look too bad, and, as I said, would allow proper functioning of the lid in all circumstances.

 

[Deadeye]

Thanks both - really helpful