Ever since man discovered that useful objects could be constructed from the wood taken from trees, one of the most important techniques needed to make these objects possible has been how to join two pieces of wood together. From early attempts to join various pieces together with strips of vine or leather to the invention of various forms of glue, craftsmen have struggled to make strong joints in order to complete useful and lasting items.
The physical properties of wood itself both hamper and assist the craftsman. Early chair makers used the ability of wood to both expand and shrink as a very successful method of joining complex chair parts. Legs of chairs for instance could be fashioned from "green" or wet wood. The cross braces would be shaped and then dried completely.
Once these dried pieces were inserted into holes, mortises, bored into the legs, the legs would shrink around the cross pieces thereby locking them into place without the need for glue or fasteners such as nails or screws.
Windsor chair makers brought these techniques to exceptional levels with specialty tools such as spoon bits which fashioned mortises larger at the bottom in effect fashioning a mortise which when dried would lock the tenon of the crosses braces tightly in place.
This shrinking and expanding of wood pieces due to humidity or lack of it is also responsible for the self destruction of many well built wood projects. Movement of wood as it expand or shrinks due to moisture content can literally tear pieces apart or at least cause loosening or splitting of wood.
Mortise and tenon joints in cabinet pieces, bookshelves, tables and other useful projects became one of the most preferred methods of joining individual wood pieces. Decorative and extremely strong dove tail joints were next developed which not only provided more area for glue to hold the joints but also produced a very elegant finished joint. In the days of hand tools these methods were very labor intensive and costly to produce.
Glue by itself does not provide adequate strength in most instances for a number of reasons. Joining end grain to cross grain as in shelves in a bookcase provides very weak joints because the end grain of the shelves absorbs much of the moisture from the glue compounds thereby weakening the joints.
As nails and finally screws appeared on the scene they were used along with glue to provide stronger joints. These techniques had their own negatives such as the time and labor necessary to countersink and then plug the holes necessary to hold the screws.
Wooden dowels used to join wood pieces has long been an acceptable method used by professional and home craftsman alike. Small round pegs called dowels are inserted into holes bored into adjoining pieces and when use with glue provide a good joint and additionally assist in the proper alignment of mating pieces.
A more recent device is the biscuit. An over shaped thin piece of wood known as a biscuit is inserted into a mortice cut with a power tool known as a biscuit cutter. These work much like dowels but provide much greater wood surface for glue to adhere to.
Recently a most ingenious method has been developed that solves most of the problems of joint construction and has become very popular with the home craftsman. The Pocket Hole Jig or Pocket Screw Jig such as the models produced by the Kreg company, simplify joint construction and make it possible for even the novice crafts person to make strong joints in wood.
Using precision machined tools known as jigs, holes are drilled through one piece and into the mating piece. Screws are then driven in. The magic behind Pocket Hole Jig technique is that using end grain of wood parts which offers a very week holding surface is avoided. The screws pass through the pieces at an angle and are in most cases invisible in the finished project.
However there are precision plugs available whee it is deemed necessary to completely hide the screw holes.
While perhaps not acceptable to the perfectionist cabinet maker who has the talent, training, equipment and customers who will pay for the labor intensive methods of the past. The Pocket Hole Jig is a boon to the crafts person who needs to build quality pieces quickly and inexpensively.
