There’s often a question along the lines of, “Will this joinery arrangement come apart or split if there’s changes in humidity”.

Most experienced woodworkers recommend joinery techniques to allow differential wood movement if humidity changes. Cross grain expands & contracts up to 3 times the amount compared to long grain of the same wood with the same humidity changes. Others say, “It’ll probably be all right (to glue cross to long grain parts)”, hoping there won’t be humidity changes of any significance perhaps…..

Until the Covid put a stop to it, I was giving some basic WW experience to ladies of my wife’s Womens’ Institute (a sort of club for ladies who like to do good works and learn things). One thing many found difficult to get was this differential wood expansion/contraction and the damage it can do to furniture glued up rather too much. So I made a demo piece.

They never got to see it (Covid-cancelled it all) but you-all can have a look at the photees.

It’s a small trivet made of oak end-grain blocks of about 30mm square, glued up inside an oak frame. Normally one would glue only the centres of the frame rails and allow the corner mitres to open whilst hiding them with brass corner bands; or some similar arrangement. I’ve made lots of big ones for kitchens, with various means of allowing for the differential expansion.

But look what happens when you don’t! That central crack is over 1/8th of an inch at it’s widest and the long side frame rails are bowed-in where the blocks have shrunk and tugged at them. Various other small cracks appear here, there and everywhere.  A startling demo of how furniture can self-destruct if over-glued with no joinery allowing differential expansion. The trivet is only just over one foot long and about 9 inches wide. Imagine what happens with something 6 feet long and three feet wide!

Lataxe