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What is the best practice for fastener installations

The installation of self-tapping wood screws should be done using the best installation practice by a trained installer. Here are a couple of points that must be taken into consideration for the installation of the screws.
  1. Screw collision. When installing longer fasteners, in a tight connection, a slight angle variation or deviation from the installation path due to grain angle influence or any other reason may create a torque increase spike. Pre-drilling may help have a more precise penetration path.
  2. Fastener deviation. The grain orientation may influence the penetration path of the fasteners. When installing fasteners at an angle to the grain, longer fasteners may be subjected to penetration path deviation, which would result in an installation torque increase.
  3. Pressing on the fastener during the installation will create additional resistance to the installation torque. This effect becomes more significant with longuer fully threaded fasteners installed in dense wood fiber. 
  4. Alignment of the fastener penetration path with the steel plate. For steel-to-wood connections utilizing inclined fasteners, a slight deviation from the intended installation path may pry the fastener head when the head gets in contact with the steel plate. Precise pre-drilling with a pre-drilling jig may alleviate the risk associated with that installation defect.
  5. Installing in a one-step process. The difference between kinetic and static friction means that stopping the rotation of the fasteners during the installation would require more rotational torque to restart the installation than the torque required for the installation in a one-step process. 
  6. Aligning the fastener axis with the drill axis. A miss alignment of the drill axis with the fastener axis is adding a moment to the rotation of the screw head. Keeping the drill axis aligned may be a challenge for fasteners installed at an angle.
  7. Installation torque. Factors influencing the installation torque:
    • diameter of the screws
    • length of the screw
    • the length of the threaded portion of the screw
    • the density of the wood
    • the angle to the grain
    • end grain
    • grain deviation
    • The acceleration of the rotation of the installation speed.
    • etc.
Additionally to this, it is critical to utilize the right tools for the installation of self-tapping wood screws. This is especially true when combining different factors that may be increasing the installation torque. Overall, a double-handle drill with low RPM and high torque transfer should be favored. Ideally, a drill that has a torque clutch as well as a progressive drive trigger in order to be able to control the torque and rotational speed. The installation should be done without excessive rotation acceleration that could create a torque differential between the screw head and its tip. Impact drills shall be avoided.