A dowel joint uses a concealed dowel to connect and reinforce the corresponding sides of a mated joint. Combined with wood glue, it makes for a very strong joint. Used for frame joints and leg and rail joints, the dowel-joint technique is an important basic skill for woodworkers.
Dowel Joint Technique
With dowel joints, either the dowel is completely invisible on the finished joint or one or both ends of the dowel are visible. The visible dowel joint is much easier to execute. Glue the joint first, then, using a drill bit the same width as the dowel, drill from one side of the joined wood through the glued and joined area and into, or into and through, the adjacent piece. Coat the dowel with glue and insert it into the hole.
For concealed dowel joints, use dowel centers or a doweling jig to accurately mark and drill holes.
A dowel center is a metal, button-shaped object with a sharp spike in the center of one side. To use it, drill a hole in one side of the to-be joined wood. Insert the dowel center, spike side out, into the hole. Then, carefully line up the corresponding piece of wood which will complete the joint, pressing the two pieces of wood firmly together. The spike on the dowel center will poke a small hole in the corresponding piece, marking the exact spot to drill. If you are working with a particularly hard wood, you may need to tap the wood with a rubber mallet in order to get a mark on the wood from the spike.
A doweling jig is helpful when you must drill several holes to install more than one dowel in a given joint. First, mark the locations of the joints. Line up the two sides of the joint in the position they will be joined, and draw a pencil line straight across the joint in each position that needs a dowel joint. Then, following the marks, clamp the doweling jig in position, adjusting the jig for the width of the wood according to the manufacturer's specifications. The jig will guide your drill as you cut the holes for the dowels.
Before you glue a dowel joint, always dry fit it first to ensure that the dowels and holes line up perfectly. Use fluted or ridged dowel sections, which allow channels for extra glue in the hole, which in turn make a stronger joint. Drill each dowel-joint hole a bit deeper than needed to accommodate the dowel so that there is space at the bottom for any excess glue that drips down from the dowel. A dowel that is inserted into a hole drilled at right angles to the grain can split the wood if the dowel is too long, so keep the dowel length for that side of the joint less than 3 inches long.