What am I talking about? Well an interesting little thing that I came upon when wedging through tenons has proven to be true and not just theoretical. I think it was about a year or two ago that Pete Galbert was talking about glueing only one side of a wedge when putting them in. I hadn't given it much thought as being anything ground breaking but once he started talking about it I realized that this was in fact what I had been doing and was significant to the longevity of chair joinery.
Why glue only one side of a wedge. I started doing it as I recall because I had heard about someone actually splitting the end of a tenon before assembling it with the mortise. I don't remember who it was. But the idea was that the tenon would have a weak area in it so that when the seasons changed the moisture content of the wood, thus expansion/contraction would happen, the stresses would simply spread the split in the tenon rather than break the glue joint.
So basically I figured that if you only glued one side of a wedge then the other side would serve as the weak part of the joint and spread rather than stress and break the glue joint. So here is the proof that it actually works. My house has been really dry. All my wood flooring has gaps between the boards and the humidity has been down around 10-20%. After coming from humid south east Texas this is all new to me.
Look at what the joints on my settee have done. One is the leg tenon coming through the seat. The other is the tenon coming through the handhold. One side of the wedge has opened up rather than there being a failed glue joint.
Very interesting, is it not.
By the way, I have been doing a lot of reading and editing of Pete's book that is due out this year. This post didn't start out as a way to plug Pete's book but I have to say that if this sort of stuff interests you then trust me you will love this book. It is packed with, among other things, little nuggets like this.