Dowels are one of the strongest wood bonding techniques. A properly placed dowel lasts a lifetime if it is correctly installed. Three factors influence dowels: the positioning, the bit and the method.
It's possible to drill a dowel hole freehand with a drill/driver without the aid of a jig or drill press, but it's difficult to drill it straight and is not recommended.
Drilling a dowel hole with a drill press is recommended, but not always feasible. Hole depth can be compromised, and placing large or long pieces on the drill press is not always possible.
The common, handheld doweling jig is the best way to drill dowel holes. Doweling jigs have stabilizing arms and interchangeable sleeves that align the bit and hold it steady while you drill.
The Best Bits
The brad-point bit combined with a doweling jig is the most common method and most accurate bit for drilling dowel holes. It has spirals just like an ordinary twist bit but instead of the blunt tip like a spiral bit, it has cutters with a sharp pilot bit at the end to keep it steady and correctly positioned.
The Forstner bit is similar to a brad point but sharpened to a higher degree, with more precision. It cuts smoother and cleaner than a brad-point bit but since it has no spirals and the shaft is narrow, it won't work with a doweling jig. The Forstner bit is the best choice when you have the option of using a drill press.
Dowel diameter versus bit size is contentious, and there's no real way to figure it out without testing. That's because dowels -- even though stated as a certain size -- are irregular. Some are crooked or inconsistent, and dowels are made from different materials. Dowels also work differently in different materials; hardwood, softwood and engineered wood react differently to dowel diameters. Some dowels graduate in 1/64-inch increments and are hard to measure without calipers.
Rule of Thumb
The general rule of thumb is to select a drill bit diameter that matches the dowel. For example, if you're using a 3/8-inch-diameter, 3-inch-long dowel -- the most common for 3/4-inch wood -- select a 3/8-inch bit. Drill a few test holes in scrap wood. If the dowel fits snug but you can twist or remove it with your fingers, it's fine. If it breaks off when you try to remove it with pliers or it gets stuck, it's too tight.
Drill A Hole
Assemble two pieces of wood together as if they were already joined. Use a trysquare to mark the center of the holes on both pieces. Make an "X" in the exact locations for the holes.
Punch a small divot in the center of the "X" with a center punch or other sharp tool.
Measure the length of the dowel, divide it in half and wrap tape around the bit at the measurement. For example, if you're using a common 3/8-by-3-inch dowel, place the tape 1 1/2 inches up from the point of the drill bit.
Clamp the workpiece to a tabletop or bench.
Insert a 3/8-inch dowel in the doweling jig. Center the sleeve over the "X" and tighten the clamp.
Insert the bit into the sleeve. Pull the trigger to turn on the drill. Apply pressure to the wood with the bit. As the bit engages the wood, continue drilling with even, consistent pressure until the tape reaches the wood, then stop drilling.
Blind Hole Spotters
Also known as dowel centers, blind hole spotters allow you to center and drill dowel holes for a perfect dowel joint. Dowel blind hole spotters fit into previously drilled dowel holes. A sharp point exactly marks the location of the coordinating dowel hole. Use these for precise dowel joints when you have difficulty marking the center with a pencil or absolutely need to get it right.