To attach the sides to the top and back one adds a ‘lining’ to provide extra gluing surface. This ‘kerfed lining’ is a strip of wood into which a bunch of saw cuts have been made that go almost through the wood, leaving a thin strip intact. This kerfed lining is then very flexible and is easy to bend around the sides as it is glued on. The most common kerfing used is placed so that the saw cuts are ‘out’ and the narrow strip of connecting wood is glued against the side. I have gone to what is called ‘reverse kerfing’, where the saw cuts are towards the side, and the thin strip of connecting wood is on the ‘inside.
I use reverse kerfing for two reasons. One is aesthetic, I think it looks better when you look in through the sound hole. A cleaner, more finished look. The other reason is structural. I have found that reverse kerfed lining, when it is glue on, makes the sides extremely stiff. Once you glue on this lining you can not flex the sides at all, even without a top or back being glued on. Reverse kerfing seems to add a lot of structural stability all by itself which I like. I glue on this reverse kerfed lining with the sides in the outside mold since the shape will be fixed by the addition of the lining.
