When creating a tenon, the edges come square. As they are milled through the table saw, a clean and straight edge is created. When creating a mortise, there are a few common methods. The first option is the simple method: to take out your chisel and mallet and do it the old fashioned way, by hand. This is a very labor-intensive method. The second, more efficient method is using a router with a straight bit.

The first option can be very time consuming and may lack consistency when cutting many joints, especially when doing production work. The second option, using a router, will always result in rounded edges within the mortise. In the end, because a square tenon will not fit in a round mortise, it will need extra hand work. The option of using a router is obviously much more efficient than doing it by hand, but there is an even more efficient and precise way to cut mortises:

Machining Mortises

The most accurate and efficient method in creating a square mortise that will best receive the tenon is through the use of a mortiser with a hollow-chisel mortising bit. A mortiser is very similar to a drill press, but the mortiser has a sliding table with a clamping mechanism, and a chuck which receives the square knife and drill bit of the mortising bit.

The major difference between the drill press and the mortise is that the drill press creates round holes and the mortiser creates square holes. These square holes are what create a great mortise for a mortise and tenon joint. When you’ve finished cutting out the mortise there is no need for further handwork. If you’ve set the thickness and depth correctly, the joint should come together with a tight fit from the machine.

Mortisers can range from a small bench top ½ hp to a self-standing and much more powerful machine. The cost of these machines can begin at MKD‌14,600.00 and go up to over MKD‌174,900.00 for high production. When working in production, a machine with a strong motor will enable you to create dozens upon dozens of perfect mortises all in a single day. For smaller shops, there are many affordable mortisers which will still give accurate results but are designed for lighter work.

The greatest feature about a mortiser is that once you set your work up, in seconds you can have perfect square mortises. This method can be repeated over and over again without deviation.

Mortisers come with the capability of housing many different sized hollow-chisel mortising bits.

What is a hollow-chisel mortising bit?

The bit used in a mortiser is a hollow-chisel mortising bit. It is made from a square, four sided chisel with an auger bit inside.  The auger bit is sized perfectly to fit inside the four sided chisel.  The machine spins the auger bit removing a circular column of material and the chisel comes up behind it to square away the rounded edges. The way the chisel works is through downward pressure by the user. The harder the wood, the more difficult it is to plunge down.  At the end of the process you get a really clean mortise.

Mortise and tenon joints are strong, reliable, and beautiful joints. This joint can be seen in timeless pieces and is testimony to its long-lasting capabilities. This joint gives support from all sides and has a large amount of glue surface. 

When creating a piece with just one mortise and tenon joint, it may not be reasonable to use a mortiser because a single mortise can be easily hand cut.

When working on a project that calls for multiple mortise and tenon joints, hand-cutting them all would be unnecessary hard labor, resulting with inconsistent joints. In a situation when you need to produce multiple mortises, there is no better option than a hollow-chisel mortiser.