This guide covers everything you need to know about self-drilling screws.
You will learn:
- What is a self-drilling screw?
- How self-drilling screws are used
- How self-drilling screws are made
- Industries that use self-drilling screws
- And much more…
Chapter 1: What is a Self-Drilling Screw?
A self-drilling screw is a type of tool that has the same design features as a drill bit or cutting tool. As the name implies, self-drilling screws do not require a pilot hole in order to perform as a fastener. Their function is governed by the same rules that apply to cutting tools, which are speed of cutting, feed rate, depth of required cut, and type of material to be connected. They are designed to work on soft steel, wood, and metals.
When making the decision to use a self-drilling screw, it is important to first consider the type of materials to be connected. The key factors for an efficient, operating self-drilling screw are the types of points, which include the flute, length, and wings.
Chapter 2: How Self-Drilling Screws are Used
The versatile and practical self-drilling screw has been in use for many years as a method for connecting materials. Since self-drilling screws do not require a pilot hole, they can rapidly and efficiently connect a variety of materials, which enhances productivity and performance.
The types and varieties of self-drilling screws makes them applicable to a variety of construction and fabricating operations. From applying metal roofing to finishing assemblies, self-drilling screws have become a valuable tool in manufacturing, fabrication, and production.
In error, many people believe that self-tapping and self-drilling screws are the same, when in fact they have different construction. The difference between them has to do with their point. The point of a self-drilling screw has a curved end that is shaped like a twist drill. Self-tapping screws are described as thread forming or cutting screws and can have a point that is pointed, blunt, or flat.
How Self-Drilling Screws are Used
Self-drilling screws for metal roofing are specially designed with a washer to form a tight seal when fastening. As with all self-drilling screws, they have a drill bit formed point that makes inserting them quick and easy.
Previous to the development of the self-drilling screw, builders had to drill pilot holes before inserting screws. Self-drilling screws have eliminated the need for this extra step, which has reduced time on jobs and made the process more efficient. The total process can be performed in a quarter of the time it took under the pre drill method.
Sheet Metal –
Metal sheets are used to frame a wide variety of products. To speed up the production process and ensure tight connections, self-drilling screws are used as fasteners. The drill-like tip of self-drilling screws is preferred over other methods of fastening due to its efficiency. Industries that use self-drilling screws for metal fastening include automobile construction, building, and furniture manufacturing.
The design and construction of self-drilling screws allows them to pierce 20 to 14 gauge metals.
Self-drilling locking screws are used in the medical field for orthopedic surgery, organ replacement, and tissue and muscle repair. As with other applications, they are preferred over other fastening methods for the speed with which they can be inserted. The requirements for their use include an exact calibration of their length and an assurance of biomechanical stability.
Self-drilling screws for framing must be able to cut through heavy duty metal studs. They have special heads designed to decrease driving torque but have exceptional holding strength. They are capable of driving through metals of up to 0.125 inches thick with an RPM rate of 1500. They come in a variety of metals to fit the operation and application.
Regardless of if the material to be drilled is metal lathe or heavy gauge metal (between 12 to 20 gauge), self-drilling screws can easily connect and frame a structure.
The unique feature of drywall self-drilling screws is their countersink head that neatly fits into the drywall without tearing or damaging the paper and avoids head pops. They are generally coated for interior applications and come in numbers 6, 7, 8, and 10 diameters. They are flexible enough to be attached to wood or metal studs and include rolled threads for added strength and holding power.
Concrete self-drilling screws are able to tap into concrete, brick, and block. Unlike the use of self-drilling screws with other materials, it is necessary to create a pilot hole for self-drilling screws to be able to tap into concrete. There are two groups of concrete screws, which include the standard sizes of 3/16 and 1/4 inch. The other group has larger diameters that are 3/8, 1/2, 5/8, and 3/4 inch.
There are several different head styles for concrete self-drilling screws that include flat head Phillips and slotted hex. Flat head screws are for applications where the screw needs to be countersunk, while with hex head screws screw head is above the surface.
Trim Head –
The uniqueness of trim head screws is their very small head and resemblance to finishing nails. The size of the head of trim head self-drilling screws allows them to countersink themselves, which makes them useful for attaching molding and trimming cabinetry.
Chapter 3: How Self-Drilling Screws are Made
A necessity for the production and manufacturing of self-drilling screws is the use of high quality and high tensile strength metal wire. This single factor ensures that the screws will perform according to their specifications and be able to maintain a firm tight connection.
How Self-Drilling Screws are Made
Self-drilling screws begin as wire that comes in different diameters depending on the gauge of screw. The wire for self-drilling screws is chosen such that it is harder than the material that it will join. The most common type of wire is 410 stainless steel, which is corrosion and rust resistant. Heated treated versions, up to 40 Rockwell C, ensure that the drill point is able to pierce harder resilient metals.
The first step in the production process is to straighten the wire before it is cut to the correct length.
The wire is fed into the heading machine where it is cut to length, transferred to a die, and preformed.
The screws are racked vertically to ensure even heating and are sent through a quenching furnace where the screws are heated to remove contaminants. They are then oil quenched to lock in their hardness.
Head Forming –
To create the head, the wire is struck with tons of force to initiate the forming of the head. This process is repeated several times until the correct shape is achieved.
There are several methods for forming screw threads, which include subtracting by cutting or grinding, deformation by rolling, molding, or casting, and additive methods. A key factor for self-drilling screws is the drill bit head that can have point sizes of numbers 2, 3, 4, and 5 with the higher the number indicating the longer the tip
To create the thread pattern, using the die method, a deformation process, the workpiece is placed between variable dies that have grooves to create the target thread depth. As pressure is applied, the workpiece is rolled, which leads to the thread pattern being pressured into the wire.
Chapter 4: Types of Self-Drilling Screws
There is a self-drilling screw to fit every form of connecting application. The variations in the type are in regard to the type of head, production wire, diameter, length, and materials to be connected.
One of the main differences between self-drilling screws is the type of head, which can be flat, pan, truss, undercut, wafer, oval, and trimmed to name a few. The other differentiating factor is whether the head can countersink or not.
Types of Self-Drilling Screws
Bugle Head Screws – Bugle head screws drive flush with the surface. They are used to fasten wood, plywood, and OSB. They have a #2 square drive with a #3 drill point.
Cement Board Screws – Cement board screws are used to attach cement board, dense wood, and light gauge steel. They have a unique rib design with a countersink head that connects flush against the board. Cement self-drilling screws have wings that ream out the surface to avoid premature thread engagement.
Eye Lag Screws – Eye lag screws or eye hole screws are used to hold wires for drop ceilings. They have a loop at the end that allows for fastening ropes, wires, or cables. Though they are bigger than standard screws, they have the common type threads.
Flat Head Self-Drilling Screws – Flat head self-drilling screws land flush with the surface and do not leave a head sticking out. They can be easily hidden with a screw covering to leave a free unmarked surface. As with other screws, flat head screws can have wings that bore through the material to create hole clearance such that pierced material doesn't climb up the shank. At a certain point, as the screw goes deeper into the surface, the wings break off.
Hex Head Self-Drilling Screws – Hex head self-drilling screws are one of the most used types since they fit easily into a socket head on a hand drill and can have Phillips or slotted heads. The types of hex head self-drilling screws include flanges, washer heads, and washer heads with bonded washers.
- Flange head self-drilling screws are used to attach metal to metal or plastic to plastic. They allow for more clamping torque to be applied.
Washer head self-drilling screws are popular for their efficiency and ease of use. They have a broad screw head and come in sizes from 1/4 to 14x1.
- Hex head with bonded washer self-drilling screws are made from bonded 410 stainless steel. The bonded washer provides a leak proof seal and is designed to drill through steel with a Rockwell C50 to 56.
Truss Self-Drilling Screws – Truss self-drilling screws have an extra wide truss that distributes pressure equally to reduce the possibility of crushing thin materials. They are made from stainless steel to avoid corrosion of rusting and are commonly used in the food, pharmaceutical, and sanitary environments. They have a very smooth finish and are self draining to avoid bacterial growth.
Oval Self-Drilling Screws – One of the purposes of oval self-drilling screws is to present a finished look. They are beveled under the head to be countersunk and are normally used on metal. Oval head self-drilling screws function much like flat head screws with the exception of the domed type head projecting above the connected surface.
Pan Head Self-Drilling Screws – Pan head self-drilling screws cannot be countersunk and have a slightly flat rounded head with chamfered edges. They are flat load bearing with the head having a moderate height and diameter. Pan head self-drilling screws have high outer edges to provide a high tightening torque.
Button Head Self-Drilling Screw – The head on a button head self-drilling screw resembles a dome with a large diameter. They can come with a hex drive that makes them easier to drive since there isn’t any slipping or stripping.
Binding Self-Drilling Screw – This type of self-drilling screw is similar to a pan head but has a thicker flat 10% larger bearing surface and deeper drive slot. They are often used to make electrical connections since their wide heads are good for holding terminals and wires.
- Hex External – has a hexagonal head that sticks out from the surface and can have a built in flange.
- Hex Internal – require an Allen wrench to install and are used where it is necessary to avoid slippage that can occur with a slot or Phillips’ driver.
- Phillips – is the most common type of driver. It has a centered cross shape, which keeps the screw in place while being driven.
- Pozidrive – are like a Phillips’ drive but have more grooves to give the impression of a star shape. They require a specially designed drive bit.
- Quadrex – is a combination of Phillips and a square recessed drive. They look like a Phillips’ drive with a squared cross section and not pointed.
- Slotted – have one narrow opening for flat head drive tools. Slotted drives are the most common type of drive and generally what people think of when speaking of screws.
- Square Recessed – have a square center to prevent cam outs. They require a square shaped extended drive and are known as Robertson drives.
- Star – have a double square Robertson drive with two squares to form an eight point star or have three Robertson squares to form a 12 point star.
- TORX – has a six point star shape. They have become very popular in the assembly of appliances and electronic equipment since they prevent cam out.
- Tri-Wing – has three slotted wings with a small triangular hole in the center. The slots are offset and deep allowing for the application of greater torque.
The ten drives above are a few of the types of drives that are used to manufacture self-drilling screws. The diagram below provides a more complete representation of the many drives available to producers.
Chapter 5: Self-Drilling Screw Considerations
In the construction and production of self-drilling screws, as well as their use, there are certain factors that need to be considered. The proper selection of a self-drilling screw can go a long way for ensuring a secure connection and rapid completion of the work.
As with any tool, proper performance can be successfully achieved by paying attention to the requirements of the tool. In the case of self-drilling screws, they can be constricted by the material used to produce them as well as the speed at which they are applied, each of which can fail mid-application if used inappropriately.
Self-Drilling Screw Considerations
Drill Point Material –
The point, that is connected to the flute, of a self-drilling screw is normally made from carbon steel since it is less stable at high temperatures unlike high speed steel used to produce drill bits. Screws should be applied using some form of drill motor for protection against wear.
In some cases, coatings can be applied, which offer greater strength and protection against rust and corrosion. A zinc coating on steel protects the steel against corrosion.
High Temperature Stability –
Drilling produces friction, which produces heat. A drill point that generates a great deal of heat will fail quickly. This can be controlled by the amount of force applied when drilling as well as the speed of the RPMs on the drill motor.
Drilling Temperature –
There are several factors that influence the drilling temperature each of which can be controlled during the application. The RPMs on the motor can be controlled by using the correct settings of the motor to fit the type of material to be drilled and the point of the self-drilling screw.
One of the common errors made when installing a self-drilling screw is the tendency to apply extra force to push the screw into the material. Unfortunately, the application of force can increase the amount of heat created by the screw.
The first consideration regarding the use of any self-drilling screw is the type of material into which it will be injected. Selecting the proper self-drilling screw can prevent a great number of problems especially ones related to the creation of heat during the drilling process.
Applied Force –
Reducing the amount of applied force can significantly remove many of the problems associated with connecting two materials. self-drilling screws are designed to penetrate several materials and connect them rapidly and efficiently. Their design, shape, and configuration has been engineered to fit certain materials effortless, without the need for extra pressure or force.
Revolutions Per Minute (RPM) –
Another common error in a construction or production operation is to speed up the process. In the case of attaching screws, it may mean increasing the speed of the drill motor such that it produces higher RPMs. Each self-drilling screw is designed to be inserted at a particular speed, which is specified by the manufacturer. Attempting to insert them at a speed that is not recommended may cause their failure.
Each type of self-drilling screw has a set of requirements to ensure their successful use. These recommendations have been tested by designers and engineers to guarantee their products will perform up to quality standards.
Chapter 6: Causes for Self-Drilling Screw Failure
The failure of self-drilling screws is closely related to their misuse since they have been tested in a variety of conditions to determine the best way they can be implemented. Many of the problems can be avoided or diagnosed at the beginning of a process.
The best idea to guarantee that a self-drilling screw is performing properly is to test it on the material to be connected. The information below can provide a form of diagnosis to determine the nature of the failure and the means to correct it.
Causes for Self-Drilling Screw Failure
The main culprit in self-drilling screw failure is force. The best way to get the best from any tool, especially self-drilling screws, is to let them do the work. Engineers and designers have perfected and developed self-drilling screws such that they can do the work under the proper conditions without any added force. Ignoring their expertise can lead to failure and loss of time on the job.
Split Point –
The self-drilling screw is being fed too rapidly into the material. This can easily be avoided by slowing down.
Tip or Point Melted Away –
Every drill bit has a pre-established cutting speed to provide successful and optimal use. This is also true for self-drilling screws. When they are applied at RPMs outside their established speed, they can overheat and melt the point and remove the cutting edges or corners. This can be corrected by using the correct self-drilling screw for the application and slowing the drill motor speed.
Self-Drilling Screw Breakage –
When a tool is used improperly, it will break. This simple rule applies to self-drilling screws. As the amount of force increases during the drilling process, greater stress is put on the screw, which causes it to work harder and break. By reducing and controlling the amount of force, the tool is able to work successfully on its own.
Reduction of Point Diameter –
The melting point of any material correlates with the amount of friction, stress, and force that is applied, which is true for the materials used to make self-drilling screws. When the point of a self-drilling screw is under stress, it produces friction, which produces heat. As the heat increases, the point melts and loses its cutting ability.
The reasons for this happening include the application of too much force, the wrong self-drilling screw for the material to be connected, or insufficient chip clearance. The corrections to these problems include choosing the right screw for the material and one with a long pilot section as well as decreasing the amount of force.
Self-Drilling Screw Does Not Drill –
When a drill bit is unable to cut into a material, it is the result of the piece to be worked being too hard for the drill bit. . The first step in deciding on a self-drilling screw is to choose one that is appropriate for the material. On the packaging and online, suppliers and manufacturers offer tips and information regarding what self-drilling screw can be used with what material. By carefully examining the requirements, this particular problem can be avoided.
Self-Drilling Screw Handling –
Self-drilling screws are a tool that need to be handled with care. When they are thrown, exposed to abrasive materials, or left in a harsh environment, they may become dull and lose their cutting edge. At the beginning of a job, it is wise to inspect the screws to ensure that they are not damaged.
- A self-drilling screw is a type of tool that has the same design features as a drill bit or cutting tool.
- As the name implies, self-drilling screws do not require a pilot hole in order to perform as a fastener.
- Since self-drilling screws do not require a pilot hole, they can rapidly and efficiently connect a variety of materials, which enhances productivity and performance.
- A necessity for the production and manufacturing of self-drilling screws is the use of high quality and high tensile strength metal wire.
- The proper selection of a self-drilling screw can go a long way for ensuring a secure connection and rapid completion of the work.