First, it is important to understand that self drilling screws and self-tapping screws are not the same items. While this may seem like a picky distinction, they are two completely different types of screws that are suited to different types of fastener applications.
In small projects around a Minneapolis home, choosing the wrong alternative between self-tapping and self drilling screws will typically not be a problem, just more of an inconvenience with tightening the fastener. With fabrication or construction projects the wrong screws have a much larger implication.
When to Use a Self Drilling Screw
Generally, self drilling screws are used in softer materials. The end of the screw resembles a drill bit, with a flat area without threads that tapers to a more or less pronounced point. From this point up one side of the unthreaded area, there is a flute or a notch that creates the drill like action, allowing the screw to create or drill its own hole in the material.
Starting the Screw
In very soft woods and materials is it possible to apply slight force to the head of these types of screws and it will start into the material. In harder materials, it may be a good idea to drill a small pilot hole just to allow the point and the flute to be able to grab into the material to start the hole and engage the threads to continue to pull the screw in. Make sure to use a drill bit that is smaller in diameter than the self drilling screw; it just needs to get the point started to be effective.
Avoid Over Tightening
With any type of screw, particularly when using an electric screw gun for installation, avoid over tightening the screw. This can result in weakening the fastener or even causing it to fail, resulting in the need to repeat the process and try to cover up the original hole.
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