Lag screw are fasteners that is used to secure heavy wooden structure, and a person must select and install lag screws correct to ensure the structural integrity of a project. A person must select a lag screw that is appropriate for specific load and the type of wood being used, because a lag screw that is too small will lack the necessary strength, and a lag screw that is too large may split the wood. The diameter of a lag screw is an important measurement, but the thread pitch and the length of the lag screw threads is also important measurements.
The length of the lag screw threads determine how much of the lag screw engage with the wood, and more engagement between the lag screw threads and the wood result in a stronger connection. Preparation of the wood is a necessary step in the installation of a lag screw, and a person should use a two stage drilling process to prepare the wood. The first stage of the drilling process is the creation of a clearance hole in the first piece of wood, and the clearance hole must be the same size than the shank of the lag screw.
How to Choose and Install Lag Screws
If the clearance hole is the same size than the shank, the head of the lag screw can pull the two pieces of wood together to create a tight clamping force. The second stage of the drilling processes is the creation of a pilot hole in the second piece of wood, and the pilot hole must be smaller than a lag screw. A person must size the pilot hole correctly based off the type of wood, because a pilot hole that is too small will cause the lag screw to snap or the wood to crack, and a pilot hole that is too large will prevent the lag screw threads from grab the wood.
Environmental factors are an important consideration when a person select a lag screw, because the environment affect the lifespan of the lag screw. If a person use a lag screw outdoors, the lag screw may rust if the lag screw does not have a protective coating. Many people use pressure treated lumber for outdoor projects, but the chemicals in pressure treated lumber can corrode standard zinc plated lag screws.
Therefore, a person should use hot dip galvanized lag screws or stainless steel lag screws for outdoor projects, because hot dip galvanized lag screws and stainless steel lag screws is more resistant to corrosion. The method used to drive the lag screw into the wood is also an important part of the installation process. Driving a lag screw into dense wood create friction and heat, so a person may apply wax or bar soap to the threads of the lag screw to lubricate the threads.
Lubricating the threads allow the lag screw to slide into the wood more easy, and lubricating the threads can prevent the head of the lag screw from snapping off during installation. If a person use an impact wrench to drive the lag screw, a person must be careful not to apply too much torque. Over torquing the lag screw can crush the wood fibers underneath the head of the lag screw, and crushing the wood fibers reduce the clamping force that the lag screw provide.
The head of the lag screw should be snug and flush against the wood, but the head of the lag screw should not be sunken into the wood.
