Loose Newel Post
Apply pressure to the loose newel post at the base of your stair rail. The idea is to move the post back into its original position against the stair treads, stair rail and side skirt board or stringer. A loose newel post causes your stair rail to loosen and to become crooked. Use your saw to cut a length of 2-by-4 inch stud to fit the gap between your newel post and a nearby wall. Wedge the wood in place with rags at each end to prevent scratches. This stud will serve as a brace, holding the newel in the proper position as you install the support anchor.
Use your power drill and bit to make a pilot hole through the newel post and into the stair tread. Start on the outside edge of the newel post, and drill inward toward the stair treads. Use a speed square to keep the drill straight, and stop drilling when you reach about 1 inch into the tread material. Drill the rest of the way into the stair tread using a bit which is about 1/2 the size of your first, larger bit. Use a countersink bit to create a notch in the newel post for your screwhead to fit.
Use your screw gun to drive an extra long 12-by-4-inch anchor screw into the pilot hole and the tread beyond. The screw will pull and hold the newel post tight in position.
Use your putty knife to apply wood putty to the hole over the screwhead. Fill the hole and scrape away the excess putty using the knife blade held at a tight angle against the post. Allow the putty to dry according to the manufacturer's instructions, then use your fine- grit sandpaper to smooth it over. Use your paintbrush to apply paint to cover the repair.
Use wood glue to tighten up a loose baluster. Squeeze glue into the space between the top of the baluster and the stair rail. The glue will fill the space and add strength to the bond between the two surfaces. Repeat the process at the bottom end of the baluster where it meets the side stringer.
Use your power drill and bit to make pilot holes through the top of your loose baluster and into the underside of the handrail above. Use your screw gun to drive wood screws into the pilot hole. These screws will provide extra strength to the joint and extra support to your stair rail. Repeat the process on the bottom end of your baluster, where the screws should mount in your side stringers.
Use your drill and bit to make pilot holes in the same manner to install nails rather than screws. Use your hammer to drive finishing nails into the pilot holes, and use a countersink to drive the heads below the surface. Fill any remaining holes or blemishes with wood putty, and sand when dry.