Introduction to Furniture Joinery
“There are three categories of woodworking joinery that we use to make furniture; the butt joint, the mortise and tenon, and the dovetail. All other joinery can be considered variations within of these three categories.” -- Ian Kirby, Master Woodworker
What is the best woodworking joint for making furniture? If you're looking for a simple answer, the bad news is that there is no single answer to this question. The good news is there are many effective methods to join two pieces of wood together, giving you the flexibility to choose the method that best suits your project and skills. This article is an overview of the most common options within the three main categories of woodworking joints; butt joints, mortise and tenon joints, and dovetail joints.
The Butt joint is the most basic and easiest joint to form. It is created by butting two flat edges, ends or faces of two workpieces together without any special machining. This joint can be used in a lot of different ways to join two boards or panels: edge to edge, end to side and end to edge.
Reinforcing Butt Joints
The butt joint is not very strong on its own, which is why it is typically reinforced. The following are the most common methods of reinforcing a butt joint.
Screws and Plugs
Screws provide a strong and secure reinforcement for butt joints. Conceal the screw heads with wood plugs. Use a plug cutter to make wood plugs to match the workpiece wood grain.
Beadlock Floating Tenons
The Beadlock® joinery system allows you to create joints with mortise and tenon strength without the need for large, expensive machinery. The flutes on the stock increase the amount of precious glue surface and also prevent the joint from racking.
Domino Floating Tenons
This Festool Domino cuts quick, precise mortises with the ease and simplicity of a biscuit cutter. One plunge creates a perfect, smooth-sided mortise that is precisely sized to accept a Domino loose tenon, creating an incredibly strong joint in stock as narrow as 7/8'' wide.
A tried-and-true method of adding strength to basic butt joints is doweling using cylindrical dowels fitted into holes drilled in both joint parts. Made of hardwood, dowels are ribbed or spirally fluted along their length, to allow glue to spread around them during assembly, resulting in a strong bond. The trick to getting good dowel joints is to use a doweling jig that will locate the holes to line up exactly in each piece; any discrepancies in location and the dowels won’t fit into both parts or the joint will be misaligned.
A popular way to create suprisingly strong butt joints is with pocket screws. This system uses steeply angled, counterbored holes drilled into one butt joint member. Screws driven into the holes pull the parts together and secure them firmly. Pocket screwed butt joints are quick to assemble and require no glue, so there’s no squeeze-out or messy drips to clean up afterwards. Pocket hole jigs such as the Kreg 720 Pocket-Hole Jig make it a breeze to drill the pocket holes.
Invented in Europe more than five decades ago, biscuit joinery (aka plate joinery) uses small, football-shaped wood biscuits glued into slots to form strong, quick-to-make joints between butt-joined wood parts. A plate joiner (above) is used to cut the slots. Carpenter’s glue swells the compressed wood biscuits, hence making a very tight, strong joint. The biscuits are a great reinforcement for butt joints used to join cabinet carcases, chests and boxes, drawers and trays or end-to-edge joined frame members 2 inches and wider.
The MILLER Dowel system is an example of a through dowel fastener. MILLER Dowels are inserted into a pilot hole that is dbored with a stepped drill bit. The stepped dowel is inserted 75% by hand because of the relationship of the dowel shape to its pilot hole. You get better holding strength, and it is easier to tap in. Another advantage of having the dowel inserted so far through the top board is that the pilot hole does not have a chance to misalign. The hole for a traditional dowel must be perfectly matched up so the dowel can enter the second piece of wood without problems.
Reinforced Miter Joints
A miter joint is simply a type of butt joint that joins two pieces cut at mating angles. Miter joints are not very strong without reinforcement because they connect end grain to end grain. You can add strength and dress up your mitered corner joints by inserting splines. The Rockler Router Table Spline Jig locks into a standard router table miter slot and features a sled that holds your workpiece at a 45° angle while you guide it smoothly past the router bit to cut the spline slots.
Mortise and Tenon Joinery
A mortise and tenon is one of the oldest, most well-known and useful furniture joints. Primarily used in solid wood woodworking to join end grain to edge grain. A mortise and tenon joint is, at its most basic, a peg fit into a matching hole.
Anatomy of Mortise and Tenon Joinery
While it may seem a bit over the top, there are at least nine parts to label when it comes to a run of the mill mortise and tenon. Do you need to know all these terms to make a successful mortise and tenon? The answer is no, but the nomenclature helps you to understand the geometry of the joint and how it can vary from use to use. For lack of a better term, we call this the anatomy of the joint, and some of the names are actually derived from our human anatomy. The specific name of the mortise/tenon piece depends on its use or function and its orientation. Most commonly, the mortise piece is usually an upright piece like a stile, while the tenon piece is usually a horizontal piece, such as a stretcher, rail or apron. This drawing will illustrate the various parts and where they occur.
VIDEO: Intro to Mortise and Tenon Joinery
Dovetail joints are one of the hallmarks of fine woodworking craftsmanship. If they are well-made, the combination of a large area for glue coverage associated with the mechanical quality of the joinery provides a durable and long-lasting joint. Dovetail joints consist of an interlocking and snugly fitted series of pins and tails. The tails and pins can be handcut or cut using a dovetail router jig .
While there are many subtle variations of the dovetail joint, the two main categories are through dovetails (above left) — where, as their name implies, the pins and tails extend all the way through the workpieces. The other main category is the "half blind" or "single lap" dovetail (above right) - called that because the drawer front overlaps the tail ends on the drawer side.
VIDEO: Cutting Dovetail Joinery with a Router Jig