CHAPTER 5, LESSON 3 of 5
GOAL: There's more than one way to design a mortise and tenon joint. This lesson will overview eight classic variations on the usual style.
In Lesson 2 of Chapter 5, I discussed the basic design of mortise and tenon joinery and outlined a number of construction objectives to help you build them for optimal strength. This lesson expands on the topic. Here, I'll illustrate more mortise and tenon styles - some which you'll rarely see made anymore - that you can explore in your project designs.
|
| |
|
| Loose mortise and tenon (above), the predecessor of today's biscuit or Domino joints. At right, a haunched mortise and tenon (top in illustration) and a long and short shoulder mortise and tenon (bottom in illustration. |
|
| |
|
|
Sloping haunch
|
Fox tail wedge
|
|
| |
|
|
Dowel pegged
|
Twin mortise and tenons
|
|
| |
|
| Through wedged mortise and tenons
|
Nearly as soon as there were woodworkers, the mortise and tenon joint was created - an efficient and elegant way to join solid wood. Variety being the spice of life and the essence of creativity, many kinds of mortise and tenon joints became common. Due to advances in machinery, adhesives and techniques, some of the mortise and tenon variations illustrated here aren't used frequently anymore. However, they are still viable options for your projects.
Loose Mortise and Tenon
A slot mortiser is a machine that cuts a mortise into both rail and stile. The two parts are connected with a third piece made to fit the slot, much like a biscuit joiner. This joint is called a loose mortise and tenon. You can make the joint using a plunge router and a single bit, although you will normally need different jigs to manage the two parts. Once glued, the joint is just as strong as a conventional mortise and tenon.
Haunched Mortise and Tenon
In the days of hand tool woodworking, grooves were made with a plow plane. Because you can't make a stopped groove with a plow, the haunch was left on the tenon to fill the groove. If the frame was to be fitted with a glass panel in a rabbet, then the long and short shoulder joint was used.
Sloping Haunch Mortise and Tenon
On a three-dimensional frame, there is no need for a groove. The notion of a haunch, however, remained. A sloping haunch satisfies the psychological need for a haunch and the visual need for a flush shoulder line at the top edge.
Fox Tail Wedge Mortise and Tenon
I have made many fox tail joints but never used one in furniture. You only get one shot at glue-up. Here the tenon fits into a mortise that does not pass all the way through the workpiece, and wedges in the tenon expand it as the rail is driven home. It's a clever concept, but there's no place in furniture where it's really necessary.
Pegged Mortise and Tenon
Draw pegging is a technique derived from timber frame construction. It's unnecessary with modern glues and correctly made joints, but if you like the look, add the pegs after the joint is made.
Twin Mortise and Tenon
When the rail is thicker than 1", you can increase the gluing area by making twin tenons side by side. The total thickness of the two tenons is about the same as for a single tenon, but the doubled gluing area makes for a potentially stronger joint. The center right illustration on this page shows typical proportions: the minimum thickness of each tenon is about 3/16", and the space between should be about equal to the tenon thickness. Twin tenons are often used this way in chair making where a back rail joins the legs.
Through Wedged Mortise and Tenon
Underframes impact stability to a piece of furniture by bracing the structure and sometimes doing double duty as shelves. Where two underframe members meet at a T-shaped junction, you can increase the gluing area by using twin tenons. If the joint is made through and wedged, it offers an attractive design detail. However, it demands precise construction. The wedge must thrust the stock against the end grain of the mortise. Place it the other way and you'll split the wood.
|