This is an excerpt from “The Woodworker: The Charles H. Hayward Years: Volume III” published by Lost Art Press.
Readers will recall that in January WOODWORKER we gave on page 8 an article “Wedging Mortise and Tenon Joints.” The following letter is from a reader who does not agree with the view expressed in it, and we publish it here as the subject is of considerable interest. Possibly readers may have other opinions about it, and if so we should welcome correspondence.
If your contributor would conduct the following experiment, he might be induced to modify his views concerning the gluing of a mortise and tenon joint as described in his article in last month’s WOODWORKER. Cut two or three inches from the end of a wide board. Repeat this, so that there are two pieces of exactly the same width and of a similar texture. Mark the width exactly on a board and soak both pieces in water until saturated. Measure this against the previous width. The wood will have expanded to a degree depending on its original water content.
Fix piece A firmly down on a board with handscrews at each end so that, although the centre is loose, the extreme edges cannot move during drying. Fix piece B to a board with handscrews all along its width so that it cannont move at any point during drying. Place both pieces in a warm atmosphere and leave to dry. In the process of drying piece A will split, but piece B will dry out without shrinkage, and will retain its new width permanently. Contrary to what might be expected, it will also be largely unaffected by small atmospheric changes. The cells of the wood seem to be permanently stretched. This experiment proves that wood will be largely impervious to atmospheric changes and will lose its customary tendency to shrink or swell, if it is held at every point.
To turn to the mortise and tenon joint, it will now be appreciated that if the whole of the sides of the tenon and the sides of the mortise are in contact and are glued, no shrinkage can take place at these points. It also follows that if part of the tenon and mortise is unglued, shrinkage and consequent movement will take place in the unglued portion, while the glued portion will remain stable if it can withstand the pull of the unglued portion so close to it. So far as strength alone is concerned, it is obvious that a completely glued joint must be stronger than one partly glued.
The conclusion seem to be: That there would be a loss of strength in a joint only partly glued.
That the unglued portion puts an added strain on the glued portion.
That a joint properly fitted and glued will not move at the shoulder any more than any other part of the joint.
— Meghan Bates