Self-Drilling Screws – How They Work

Self-Drilling Screws eliminate the need for separate drilling and tapping operations, helping provide the user with a faster, more economical installation process. Self-Drilling Screws operate on the same basic principles as a drill bit or other cutting tool. Performance for these screws are determined by cutting speed, feed rate, depth of cut and the working material being drilled into.

Optimal Performance Conditions for Self-Drilling Screws

 

Proper installation of self-drilling screws depend on a number of factors and can (mostly) be controlled by the user. The table to the right, can be used as a guide to help properly install different nominal screw sizes.

*Suggested combined maximum values. Values may be increased or decreased, as long as associated variable are changed proportionally.

• Screw Point Geometry – the shape of the self-drilling screw drill point, not directly adjustable by the user
• RPM – the speed of the drill/driver motor while installing the screw. Can be adjusted using a variable speed drill/driver
• Applied Force – a measurement of the force applied by the user as the screw is installed, more force is not necessarily better
• Work Material Hardness – the material’s resistance to drilling or cutting, in most cases, the harder the material, the more difficult it is to drill/cut

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Important Features to Consider When Choosing a Self-Drilling Screw

When selecting the correct self-drilling screw for your application, there are a number of factors to take into consideration. This includes the types of materials being attached and the thickness of the materials. In addition to the working material, the following design features should be also be considered before selecting your screw.

• Drill Flutes – allow the drilled material to exit the hole, once completely embedded, the flutes can no longer remove these chips. These chips contain approximately 80% of the heat created during the installation process. If these chips buildup, this could cause the point to over-heat and fail.
• Point Length – determines the thickness of the material which the screw can dependably drill through. The pilot section of the drill point, unthreaded portion, must be able to drill through the working material before the threads engage completely. Fasteners can bind and break if the threads engage before drilling is complete.
• Point Wings – are not present on all self-drilling screws, they are used when you need to fasten thicker materials, such as wood to metal applications. When drilled, the wings will enlarge the hole in the fastened material, allowing the threads to pass through without engaging the threads. This added clearance prevents the separation of the materials being fastened together, known as jacking. The wings will then break away once the come in contact with the metal before the threads engage the metal.

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Don’t Forget About

• Screw Drill Point Materials – are usually plain carbon steel which is less stable at high temperatures. To help reduce the wear on the drill point, fasten using a motor drill rather than an impact driver or hammer drill.
• High-Temperature Failure – the heat generated when drilling in self-drilling screws affects how quickly the drill point fails. For additional information on this, please refer to the troubleshooting guide below.
• Drilling Temperature – motor RPM, applied force and work material hardness all contribute to the the drilling temperature. Increasing any of these values also increases the heat generated.
• Reducing Applied Force – this can help increase durability, allowing the drill point to penetrate thicker materials.
• Reducing Motor RPM – this can help improve the drilling performance into harder materials. This will allow the user to push harder during the drilling process and extend the drill point life.

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Drill Point Failure Examples

Checkout Tanners Self Drilling Screw Selection Guide