How do I Choose the Correct Self-Drilling and Self-Tapping Screws??

Self-Drilling Screws

Self-Drilling Screws operate on the same principles as drill bits and other cutting tools. This means that the way in which these screws are used affects their performance as much how they are designed.

Two important factors to consider when selecting a self-drilling screw are, material thickness and types of materials to be joined.

Screw Suitability

Optimal Cutting Parameters by Screw Size

 

 

 

 

 

 

Key Design Features to Consider when Selecting a Suitable Self-Drilling Fastener

  • Drill Flute

    • The length of the drill flute determines the metal thickness that can be drilled. Drill flutes allow the drilled material to exit the hole. If the drill flute becomes completely imbedded in the material, the drill chips will clog the flute and cause the cutting action to cease. If this occurs, the heat from the drill chips could cause the drill point to become over-heated and fail.

  • Point Length

    • The drill point is the unthreaded section from the drill point to the first thread. This length must be long enough to completely drill through the material before the threads engage. If the threads engage too early, they can cause the fastener to bind and break.

  • Screw Wings

    • It is necessary to use fasteners with wings when fastening wood, over ½” thick, to metal. The wings will ream a clearance hole and keep the threads from engaging too early. If the threads engage too early, this could cause a separation of the fastened material from the base material (jacking). Once the wings hit the metal material, they will break off allowing the threads to engage.

 

Self-Tapping Screws

Self-tapping screws can tap its own hole as it is being driven into it. They can come with a sharp, piercing tip or a flat, blunt tip. Sharp tipped self-tapping screws are designed for drilling their own hole in soft materials. The flat tipped self-tapping screws will need a pilot hole drilled before being installed. Some self-tapping screws are also self-drilling screws. These screws have a drill-like flute tip that looks like the tip of a center drill, along with the tap-like flute in the leading threads. These screws are very efficient in hard substrate applications.

How the Self-Tapping Ability is Created

  • Hard Substrates – Metal or Hard Plastics

    • Often created by cutting a gap in the continuity of the thread on the screw, this generates a flute and cutting edge similar to those on a tap.

  • Soft Substrates – Wood or Soft Plastics

    • The self-tapping ability can come simply from a tip that tapers to a gimlet point (no flute is needed), the point forms the hole by displacement of the surrounding material rather than any chip forming drilling / cutting / evacuating action.

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