Dowels are pins used to adjoin two pieces of material on the surfaces that meet each other. A dowel is completely hidden once the two parts are joined together. Various types of drills are used to make holes for the pins, but these holes must align precisely on the adjoining pieces for the pins to connect them properly. Both pieces must be marked to show how they meet and then both drill holes marked with matching center points. A simple tool effectively transfers the center point from one hole to mark the location of the drill bit center for the other.
Fit the two pieces together to be joined by a dowel exactly as they are to be assembled. Mark the outsides of the pieces with a continuous pencil line that crosses both at the points where dowels will be installed. At least two dowels are needed to prevent lateral shifting.
Mark the center points for dowel holes on one piece. Place a square along the outer pencil mark to transfer the mark to the edge that will receive the dowel. Measure the new line to find the center and mark that point with a perpendicular pencil line. Replicate this process for the other dowel hole on this piece.
Drill the holes on the marked piece with a drill press if available. Use a drill bit of the same width as the dowels. Drill the holes 1/8 of an inch deeper than half the length of pins. A drill press has a depth gauge for setting the hole depth, and a drilling table that is precisely perpendicular to the drill bit. Clamp the stock into a vise and measure the depth on the drill bit itself for hand drilling. Wrap masking tape around the bit with the lower edge at the measured depth. Drill the holes slowly and steadily to the precise depth. Use both hands for stability when using a hand drill.
Fit a dowel center of the matching diameter over one of the holes. A dowel center fits the hole like a cap with a top flange that positions a sharp protruding point in the center.
Place the adjoining pieces together as they assemble with the outer pencil marks aligned. Press or clamp the pieces together to force the point on the dowel center into the precise center of the joint hole location. Pull the pieces apart and transfer the dowel center to the other hole. Press the pieces together aligning the pencil marks to mark the center of the other hole.