In the world of woodworking there are many ways to join pieces of wood together.
When considering which joints to use, the questions you need to ask yourself are “what’s the application?”, “what will be the stress on this joint?”, and “will it be seen?”. With an array of possibilities it usually comes down to cost in both time and material.
With the advancements of adhesives (glues) and fasteners (nails and screws), proper woodworking joints are disappearing. So in an attempt to understand some of the skills and knowledge of these joints let’s have a look.
There are seemingly endless variations and combinations of common woodworking joints, so I can’t list them all, and discuss the pros and cons of each. I will look at some well-known, common joints to give an idea of what makes it good for the application.
- The Butt Joint – this joint is by far the simplest joint and must be used with adhesives and fasteners. The Butt Joint is made by placing 1 side or end of a piece against the side or end of another piece. This joint is very strong when resisting forces from above such as 2 posts supporting a beam. The intersection where the beam lays across the top of the post would be called the Butt Joint and the beam can now support a load because of the posts are holding it up.
- The Mitre Joint – this joint is for hiding the end grain of a board by cutting the desired angle in half on each of its pieces. Meaning a 90 degree corner will be made up a 45 degree angle on the 2 adjoining parts. It is an inherently weak joint when not supported by additional means. The appeal for this joint is aesthetic. It is often used for picture frames; it keeps the profile of a moulding moving around what is being framed.
- The Lap Joint – is formed where 2 pieces cross each other or meet each other. There are many different types of lap joints: over lap, full lap, half lap, cross lap, end lap, and middle lap. Some of these joints are weak and others are stronger. Some rely on fasteners and others, when fitted properly, are a mechanical joint and can hold themselves together. Lap joints are often used in conjunction with other joints where a particular outcome is desired. Such as a half lapped mitre joint or the full lapped dovetail.
The Groove, Dado and Rabbet (Rebate) Joints – The Groove joint is a 3 sided channel in the wood parallel with the grain. The Dado is a 3 sided channel moving across the grain. The Rabbet is a 2 sided channel moving along or across the grain of the board. All 3 of these joints are meant to accept another piece into the channel which was cut. These joints are a form of the Lap Joint, another joint which, as I mentioned before, can take on many, many forms. In some cases these joints can be very strong-where the application is similar to the Butt Joint-like in a bookshelf. Other times these joints are used to conceal the intersection of the joint, as in the finished end of an upper cabinet, so the edge and joint of the back and bottom are not seen.
The Mortise and Tenon Joint – this joint is formed with 1 piece being cut with a mortise. Which is a recess in the piece made to receive the tenon. The other piece is cut to form a tenon, a projection of the piece made to fit into the mortise. The closer the fit between these 2 parts the better the joint will be. The mortise and tenon is the strongest joint to handle the stress of racking. Most often seen in furniture and wood framed doors. Racking is a kind of rotational stress, where there is compression and tension applied to the joint at the same time. The reason the mortise and tenon joint can handle this stress is because the tenon is enclosed in the mortise and the joint relies on the strength of the wood to hold it together. If the wood involved in the joint fails, then the joint fails. It is not dependent upon adhesives. One advancement to the mortise and tenon joint was the addition of the “pin”. The pin was a piece of dowel inserted through the entire joint to add strength, security, and even beauty. No matter how old the item is, or loose and sloppy the joint fitting is, if the joint is “pinned” it becomes a mechanical joint holding itself together.
And lastly, The Dovetail Joint – this joint is the icon of woodworking ; it is associated with quality,craftsmanship, and style. However it is not the do-it-all joint. It, too, has it’s place among the other joints. The dovetail joint is a mechanical joint and, when cut properly, it holds itself together. In fact, it needs no adhesives or fasteners.It is also known as the drawer joint because of its superior holding power against tension (being pulled apart). As drawers are repeatedly pulled open the dovetail joint continually holds together. It is a time consuming joint to machine/cut and so in today’s world it is seen when the consumer is willing to pay for the added strength of the joint. The dovetail is not just for drawers, although a common place for it. This joint is also seen in furniture where it holds together items that may be under stress to separate such as a face frame on a bank of drawers; the gables may bow under the weight, thus the dovetailed face frame holds everything in line and square. It is also used on the rungs on a chair because the downward pressure causes the legs to separate.
These are some of the basic joint used in woodworking. They can be combined to create very strong, sophisticated joints for a particular application. Don’t rely on just adhesives and fasteners the next time you build a drawer, cabinets, bookshelves, a deck, stairs, or anything else out of wood. Use a joint that is designed for the stress and relevance of its purpose and work load.