Selecting the correct length of wood screw is a necesary step in woodworking because the correct length of wood screw ensures that joints remains stable and strong. If a person select a wood screw that is too short, the wood screw will not penetrate the base material deeply enough, and the wood screw will fail to hold the boards together. When a wood screw fails to hold the boards together, the structure will wobble or pull apart when a load is applied to teh structure.
A person can determine the correct length of a wood screw by using the rule of thirds. This rule states that at least two-thirds of the total length of the wood screw should be buried in the base material. The wood screw passes through the first board and then the wood screw enter the second board to create a grip.
How to Choose the Right Wood Screw Length
For example, if the first board is three-quarters of an inch thick, the wood screw must be long enough to pass through that three-quarters of an inch and then penetrate the base material by a significant amount. You should calculate the total length so that the wood screw reaches deep into the base material, and you should round the total length up to the next standard size to ensure the wood screw is long enough. The type of wood a person uses will change how a person apply the rule of thirds.
Softwoods, such as pine or fir, have soft wood fibers that allow the wood screw to grip easy, so a person may be able to use a slightly shorter wood screw in softwoods. Hardwoods, such as oak, have dense wood fibers that are difficult to penetrate, so a person must ensure that the wood screw meets the full two-thirds requirement in hardwoods. If a person does not use a long enough wood screw in hardwoods, the dense wood fibers may cause the wood screw to strip or fail.
Different projects require different type of wood screws and different lengths of wood screws. When you are hanging cabinets, you are driving a wood screw through plywood and into a wooden stud. If the wood screw is too short, the wood screw will not reach the center of the stud, and the cabinet will sag toward the floor.
When you are installing subfloors, you must use wood screw that are long enough to sink into the joists but not so long that the wood screws poke through the top of the subfloor. Additionally, fencing projects require thicker wood screws because fencing must resist the twisting force of a wind. The availability of wood screw sizes and the head type of the wood screw also affect the installation.
Thinner wood screws are often shorter and are used for crafts, but thin wood screws are not suitable for framing. Heavier wood screws are often longer and are used for heavy timber. You should also consider the head type of the wood screw because the head type changes how much length is used.
Flat head wood screws are designed to sit flush with the wood, but flat head wood screws require a countersink hole, and the countersink hole reduce the effective length of the wood screw. You should add an extra eighth of an inch to the length of the wood screw if you are using flat head wood screws to compensate for the depth of the countersink. The material of the wood also dictates which type of coating a wood screw must have.
Pressure-treated lumber contains chemicals that can corrode cheap zinc finishes, so you must use galvanized or stainless steel wood screw when working with pressure-treated lumber. Cedar wood can cause stains when it comes into contact with plain steel, so you must use coated wood screws when working with cedar. Medium-density fiberboard, also known as MDF, is a material that crumbles easy at the edges, so you should limit the length of the wood screw in MDF and always use a pilot hole.
Many mistake can occur if a person does not plan the installation carefully. If a wood screw is too short, vibrations may cause the wood screw to pull free from the wood. If a wood screw is too long, the wood screw may split the base material or the wood screw may poke through the other side of the wood.
To avoid these mistakes, you should pre-drill pilot holes in dense woods, and you should use coarse threads when you are working with soft wood grains. Finally, you should select the correct drive type, such as square or star drive, because these drive types grip the wood screw more securely then Phillips drive wood screws when you are using a power tool.
