How to Cut a Mortise in a Fence Post

One of the tidiest and strongest ways of securing the horizontal rails to a fence post is to mortise the rails. A mortise is a cut opening into which a piece of wood, commonly referred to as a "tongue," is inserted. A mortise if far stronger than a surface mounting and more attractive than any type of bracket. The method for cutting a mortise into a fence post is common to a mortise of any size for any type of fence rail board.

Step 1

Lay out the desired location of the mortise opening on the side of the fence post. Use a hand square to connect the lines to form a square outline for the mortise hole.

Step 2

Cut the perimeter line of the mortise using a wood chisel. Place the flat side of the chisel tip on the line and tap the chisel with a hammer or wood mallet. Repeat the action until the full perimeter of the mortise has been scored.

Step 3

Chip out the interior area of the mortise outline, cutting toward the inside and pivoting the chisel to remove the wood chips. Chip out a minimum of 1-inch and a maximum 2-inch depth for proper fence rail support.

Step 4

Repeat Steps 1 through 3 to complete the mortising of all the fence posts, as needed.