Engineering professionals specify a variety of fasteners for metal building and roofing applications. They make their selection based on many critical factors including how well they will secure the panel, trim or flashing to the substrate. When properly installed, they have confidence that the connection meets the requirements of the overall system.
Because installation is a major factor as to how well the fastener performs, it is important to use care during installation and follow some basic techniques that will contribute to producing a secured connection.
Types of screws for fastening to a steel substrate
The most popular fasteners used for these connections are self-drilling tapping screws. They are designed to drill and tap steel in a single operation. Here are some tips that will assist you in assuring you get the best performance.
Match the drill point type of the screw to the thickness of the substrate
Drill screws are available in various drill point types (sized by a number) that are capable of drilling and tapping various thicknesses of steel. The larger the drill point type (number) for a given diameter, the thicker the steel it will drill and tap.
It is important to select a drill point type that meets the drilling thickness capacity of the screw diameter. This chart shows a few of the more popular sizes used in metal building and roofing connections.
Determine the length of the screw
The length of the screw is determined by the measuring the total distance of the materials being fastening together, and adding an additional length so that at least three full threads extend beyond the substrate. This will ensure full thread engagement and produce optimal pullout loads. Use the following chart to assist in determining the minimum screw length.
Power tool tips
For a fastener to perform to its optimum level, install them according to the supplier’s recommendations- and be sure that the appropriate installation techniques and correct tooling are used.
• Screws should be installed using a 2,500-rpm maximum screw-gun.
• Use 2,000 rpm or less when installing into 1/4-inch thick steel or greater.
• The screw-gun should include a torque control or depth-sensing feature to minimize damage to the sealing washer and reduce the possibility of over-driving the screw to failure.
• Impact tools are not recommended for installing drill screws. They can easily exceed the torque strength of the screw, which can cause strip-out and/or screw breakage
Accessory tips
Worn out or inexpensive drive bits and nut-setters can cause poor drilling performance, strip the recess, and damage the paint on the screw.
When using hex drive sockets, be sure to “set the magnet” so that the hex head of the screw fully engages into the hex of the drive socket.
Using good high-quality accessories will eliminate wobble and improve drilling performance.
Installation tips
Drill screws perform best when they are installed perpendicular to the surface using medium pressure. This allows the drill point to penetrate the steel without causing excessive heat that can reduce drill times. Be aware that all the drilling must be complete before tapping begins, or damage to the drill point will occur.
Understanding how screws perform and using proper techniques will help the installation of selfdrilling screws. Using these few tips will produce performance that is more consistent and will help in assuring the design loads are achieved.
Joe Stager is the vice president of product development and marketing at Cleveland-based Triangle Fastener Corp. To learn more, visit www.trianglefasteners.com.
