How to Make Mortise and Tenon Joints
Woodworking Joinery Techniques made Easy without Dovetails
Mar 26, 2009
This manner of woodcraft joining has a rich history indeed, including the assembly of the 30 sarsen stones of Stonehenge. According to National Geographic magazine, “its massive lintels are bound to their uprights by mortise-and-tenon joints taken straight from carpentry, an eloquent indication of just how radically new this hybrid monument must have been.”
Anatomy of a Mortise and Tenon Joint
It's very simple in theory – it's composed of a tenon (a “post” commonly square or rectangular although it may be round) and a mortise (the hollowed out portion) that receives the tenon. Just like assembling Christmas gift toys, part 'A' fits into part 'B'.
When the tenon is formed by cutting away wood, the surface left perpendicular to the length of the stock (called the shoulder) forms a 90-degree angle to the tenon and flushes up to the mortised stock, effectively making a “blind” joint.
The real trick, and the key to success, is to make the fit precise and snug. The ample amount of open-grain contact (4 sides of the tenon and 2 or 4 shoulders) makes this one of the strongest members of the wood joinery line-up.
Contrast this with the simpler but weaker half lap joint.
Ways to Cut the Joint
Traditionally, the basic tools are the hammer and wood chisel. Like that old joke, “How do you carve an elephant? Simple; start out with a square block and chip away everything that ain't elephant!”
But seriously, there are better techniques today. Mortising machines are the most common way of making the receiving end. These operate like a drill press; some cut only round holes, and some cut both round and square ones.
The most precise method of cutting the tenon is using a table saw with a stacked dado set. The tenon should be no thinner than 1/2” the thickness of the stock in either direction. Then the receiving mortise can be made by first using a drill press to make a set of side by side holes first (if not using a mortising machine).
Then, finish the mortise by cutting out the scrap with a wood chisel. This is a process of dry-fitting and fine-tuning. It's time-consuming but results in a strong joint that makes a statement about craftsmanship.
Securing the Joinery
There are two basic methods of securing the two pieces of stock, and they may be combined. First, glue is applied to one or both sides and the surfaces are mated and clamped up.
- Note: It is important to note that when repairing or refinishing antique furniture, the original kind of glue must be used to retain antique status. This is usually hide glue.
The second method is to assemble the stock and then drill two or more holes and glue in dowels.
A Variety of Joints
There are many flavors of mortise and tenon joints. The particular one used depends on both function and the look the craftsman is going for. Here are a few of the most popular ones:
- Through – Where the mortise is cut all the way through the stock.
- Stub or blind – Like the through but the mortise only goes part way through
- Twin or multiple – Two mortises and tenons; twice the effort to make, but twice as strong (double the open grain).
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