A dowel joint is a neat, strong way of making corner and in-line joints between two pieces of wood of the same dimensions. If done correctly, the joint will appear almost seamless, without any visible dovetails, brackets or screws. The hardest part of making dowel joints is drilling the holes accurately.
Select pre-cut dowels that are about a third of the board's thickness for maximum strength. You should use at least two dowels when making a right-angled joint in two planks of the same width and thickness, such as the side and top of a bookcase. The holes in the edge of the upright board butting against the underside of the top board should be spaced about a board thickness from each end. The depth of the hole should be half the width of the standard pre-cut dowel, plus a 1.5 mm (1/16 inch) space to allow excess glue to expand into.
Mark the centre point of the dowels on the edge face of the upright board with a carpenter's square and pencil. Clamp the board edge-up, vertically into a vice. Use a spirit level to line it up. Measure the required hole depth on the side of a 3 mm (1/8 inch) pilot drill with a ruler. Wrap a strip of masking tape around the shaft to act as a depth guide. Clamp the drill into the chuck of a hand held power drill.
Place the drill bit on the first dowel-centre mark. Turn the chuck by hand to start the hole in the correct position. Hold the drill in both hands and line it up carefully at right angles to the edge and the face of the board. Switch the drill on and drill the pilot hole slowly and carefully to the correct depth, keeping the drill lined up while doing so. Repeat with the second pilot hole.
Measure the hole depth on a drill the same diameter as the dowels and wrap a piece of masking tape around the shaft at the correct depth. Clamp the drill into the chuck. Place the point of the drill in the pilot hole and carefully drill the dowel hole as described above. Repeat with the second hole.
Insert a correct-diameter dowel centre into each hole. Dowel centres are round pieces of metal the same diameter as the dowel. They are shaped somewhat like a flat-headed rivet with a sharp point protruding from the centre of the rivet-like head to mark the corresponding hole position in the board to be joined.
Lay the drilled board containing the dowel centres on a smooth, flat surface. Stand the board to be joined upright and at a right angle to the edge. Use a straightedge as a guide to align both boards. Press the joint surfaces together. The sharp, pointed dowel centre will mark the correct mating dowel positions on the face of the upright board.
Drill the two mating dowel holes on the face of the second board to the correct depth using the same procedure as described above.
Smear a generous coat of quick-drying wood glue on to two dowels and tap them into the holes in the edge of the first board. Pre-cut standard dowels are machined with glue slots to allow glue and air to escape when they are driven into the wood. Apply glue to the joint faces of both boards -- add more glue to the protruding dowels and join the boards. Use two adjustable woodworker's bar clamps to clamp the dowel joint firmly together. Wipe off any excess glue with a damp rag.
Wear safety glasses when drilling wood.