Hello everyone,

There is something I don’t quite understand, even after watching dozens of Paul Sellers videos.
When we use screws joining two pieces of wood, we have to keep in mind that it is necessary to leave space for expansion and contraction to occur (I’m remembering the previous project, for example, where the drawer runner was screwed to the side of the side cupboard and one of the screw holes was wider than the screw itself).
However, when the pieces are glued together (imagine the top of that same side cupboard dovetailed with the sides), how will there be expansion and contraction without cracking the wood?
Or for example, the rail of a table glued to the legs with mortise and tenon: there is no room for expansion and contraction of the rail.

Thanks.