A newel, or banister post, is the large post supporting the end of a banister or stair rail. They are typically mounted one at the bottom and one at the top. There are a number of ways to install newel posts. In choosing your installation method, the type of newel being installed is the prime factor. The two basic styles of newel are turned solid posts and box newels. Solid posts are typically mounted with metal L brackets; the hollow box newel is typically installed on a mounting block made from two-by lumber.
Mark the location of the newel on the bottom or top stair tread, or on the landing above the top stair, or the floor below the bottom stair. This depends on the length of your railing. If it is long enough for either option, then it is a matter of taste. Use a tape measure and pencil to find and mark the location for one front corner. Place the newel on this mark. Use a square to position it in line with the stairs.
Draw the outline of the post base in the proper location. Position four 1-inch L brackets, one in the centre of each side of the post. Mark the screw holes on the floor and the post. Drill shallow pilot holes with a 1/8-inch bit in each marked spot on the floor. Lay the newel on a level surface and drill similar pilot holes in each marked spot.
Attach the brackets to the floor with a 1-inch wood screw using a cordless drill. Set the post back into position in the centre of the brackets. Attach it with screws in each hole. Drive a screw into each empty hole in the floor side of the brackets.
Glue and nail the four pieces of base moulding to the sides of the newel base. They will be dadoed, or notched, to fit over the L brackets, concealing them.
Measure the inside of the hollow post bottom. Cut a piece of 2-by-10 to fit the inside of this square with a mitre saw. Test for proper fit by placing the lumber square inside the bottom of the post. It should fit without being forced. Trim the piece as needed with the mitre saw. This is your installation block.
Measure and mark the post's position as for turned posts. Draw a second square inside the outline the size of the mounting block. Space it equally from all sides.
Drill pilot holes through the lumber square, one an inch in from each of the corners, and one in the centre. Countersink each pilot hole slightly so that screw heads will run flush with the surface of the installation block.
Set the installation block inside the marks and drive a 3-inch treated deck screw through each pilot hole in the installation block. Drive the screws through the block tightly until the block is pulled snugly to the floor.
Set the post over the block and drive two 1 5/8-inch drywall screws through each side of the post into the installation block. Glue and nail the four pieces of post base trim to the post to cover the screws.