|Mortise-and-tenon joints are one of the strongest and most used joints in woodworking. Mortise-and-tenon joinery is used for almost any project that has frame construction and needs to be as strong as possible. Chairs and tables fit this category as does almost all Arts and Crafts and Mission style furniture.
Mortise-and-tenon joints come in several types — stopped/blind, through, angled, wedged, and many more — but they all consist of the same basic parts: a mortise (a recess cut into a piece of wood that accepts a tenon) and a tenon (a tongue at the end of a board that fits into a mortise).
The tools listed below (except the Trend model) use a square hollow chisel with a matched drill bit in the center. As this is lowered into the work piece, the square hollow chisel cuts the corners while the drill bit cleans out the rest in the middle. It is fast and easy to cut the same size mortise over and over. The chisel/drill bit lasts for a very long time and can be sharpened as well.
Some manufacturers are:
Trend Mortise and Tenon Jig - $300 and used with your router
Jet JBM-5 Mortising Machine - $275 it is a dedicated bench top model
Fisch Heavy Duty Mortiser with Stand - $800 it is a dedicated floor model
Delta Mortising Attachment for use with your bench top drill press - $40
DELTA Deluxe Hollow Chisel Mortiser Model 14-651 - $270 (my favorite)
POWERMATIC Hollow Chisel Mortiser Model 719A - $900 floor model
Now for a cutting lesson using your hollow chisel mortiser:
1. Mark the mortise on your board.
2. Choose a mortising bit that matches the width of your mortise as closely as possible (without going over).
3. Set the fence so that your work piece is positioned correctly under the bit.
4. Set the depth of cut on the tool.
5. Drilling slowly, make your first hole at one end of the mortise.
6. Make the next pass at the other end of the mortise.
7. Overlapping by half the width of the bit, drill/chisel out the rest of the mortise.
8. Clean the hole up with a chisel if necessary.
This will depend on your bit and the model of tool you have. Some cut cleaner than others.