In typical machinery, we are using different types of screws. The purposes of screws are changing according to the type. Also, one of these screw types is set screws. They are also very important for such applications. You can find detailed information about them here. The general topics that we mention here;
- What is a set screw?
- What are the types of set screws?
- What are their standard designations of them?
- General applications.
- Advantages and disadvantages of them.
What is Set Screw?
Set screws are the intermediate machinery screws to prevent the relative motion between the mating parts. For example, we use them in the attachments of the hub of gears and the shafts. So, they prevent the rotation between them.
We attach these screws through a hole on a hub. And the tip of the screw contacts with the attached shaft to that hub. So, this configuration provides a better attachment between the hub and shaft. And also, there is an extra force for the attachment.
Generally, these types of screws are not designed to carry heavy loads. The purpose of the set screws holds the part in the intended positions. If there is a very heavy load, these screws will be damaged.
Headless set screws were very common in lots of kinds of mechanical applications. But in history, these types of screws caused lots of industrial accidents. So, the use of these types of screws is prohibited in many countries.
Types of Set Screws
According to the different purposes and applications, there are lots of types of set screws on the market. For different applications, we can select one of these types. All types have common advantages, disadvantages, and special features. The general types are;
- Knurled cup screws,
- Plain cup screws,
- Soft-tipped screws,
- Dog-point screws,
- Ballpoint type,
- Flat set type,
- Oval set type,
- Cone set type.
Knurled Cup Set Screws
If we compare it with the plain cup type, this type has a tooth design at the one end of the screw. We call this structure knurls. The knurled side comes into contact with the surface of the part that we attach. So, it provides a biting action and better assembly.
This biting action provides more strict assembly. So, knurled cup screws provide more mechanical stability and they will not loosen with the vibrational effects.
The most important drawback of the knurled cup type, it creates scratchings on the surface of the part. This is because of the biting effect of the screw. So, we need to use these types of screws in permanent assembly applications. We do not recommend detaching and attaching this part continuously.
Plain Cup Screws
These types of screws are the most common ones that we use in applications. At the one end of plain cup set screws, there is a concave cup shape. In the attachment of this type of screw, the force is applied to the part that is attached.
The locking effect of the plain cup screws is good. But the most important drawback is, that they can loosen with the vibrational effects. Also, with the applications of dynamic loads, it can scratch the surface.
At the end sections of soft-tipped set screws, there is a soft material. This soft side comes into contact with the surface of the attached part.
This soft side provides smooth contact with the attached part. So, there will no markings and scratchings on the part that we attach.
Dog-Point Set Screws
This is a very useful type of set screws. There is a protrusion at the end of the screw which is assembled inside a recess on the other part. So, there will be an additional mechanical connection between the screw and the part.
So, this structure provides more rigid mechanical structures and also more rigid attachments. With the dog screws, we generally obtain permanent assemblies. But also, we can disassemble the assembly without any problem.
Also, half-dog-point types have smaller protruded ends if we compare them with the other ones.
The most important drawback of this type is an extra hole on the shaft can lower the total mechanical strength.
Ball Point Type
As you understand from its name, the edge of these types of screws has a ball shape. They are very useful in applications where the surfaces are not parallel to each other. So, point connection provides a better connection between the types.
Flat Set Screw
Also, these types of set screws are very common in general applications. The ends of these screws are completely flat. So, there is contact between the shaft and the flat side of that screw.
The benefit of the flat side, it provides more even distribution of load on the surface of the part. And also, it does not scratches the surface of the part.
Another benefit of the flat types, we can detach and attach many times.
The tip of these set screws is oval. This ovalness provides a point contact between the surface of the part and the screw. So, it provides a smoother attachment and is less harmful to the surface.
Also, the movement of the shaft according to the oval type set screw is allowed.
Cone Point Set Screws
This is another type of set screw that we use in permanent or semi-permanent assemblies. Because the cone tip penetrates to the surface of the shaft which provides a more rigid mechanical attachment.
Cone point screws are best for carrying the axial and torsional forces.
Set Screw Standards and Designations
Like other mechanical elements, set screws have also standards. They are manufacturing them according to the standards of different countries. Like the other screw types, there is American and Metric discrimination between these screws.
There are different dimensions for metric set screws available in the market. The general dimensions are; 1.6, 2, 2.5, 3, 4, 5, 6, 8, 10, 12, 16, 20 and 24 millimeters. You can use these different nominal diameters in different applications. Also, the length increments of the metric screws are between 0.5 to 4 millimeters according to the length.
We are showing these screws in technical drawings according to the standards. To understand this standard, check the example below;
- M12-1.5X10 HEX SOCKET HEAD SET SCREW
This is an example of how to show the screws on engineering drawings. So, it is very basic to read. M12 gives the information about the nominal diameter of the set screw. 1.5 is about the thread specification. And 10 is the total length of the screw. HEX SOCKET HEAD SET SCREW is the type of screw.
In the American standards of set screws, the nominal diameters are between 0 and 2″. Also, the length increments of these screws are between 1/32″ to 1″.
Also, showing the designation of American screws is very simple. Check the example below to understand it.
- .400 X 16UNF-2B X .75 SQUARE HEAD FLAT POINT SET SCREW
So, it is very basic to understand general information from this statement. .400 gives the nominal diameter of the screw. 16UNF -2B is about the standard of the thread. .75 gives the length of the screw. Also, SQUARE HEAD FLAT POINT SET SCREW is the type of screw.
Furthermore, you can write the abbreviation of the type like this; SQH FP SCCR
Drive Types of Set Screws
Above all, the drive type of the screws is also a very important parameter in the structural design. Because we are using screwdrivers to attach and detach screws. It is very important to know which kinds of drive type we need to use in these set screws.
In these types of drives, there is a square recess at the head of the set screw. It is not common as the straight slot drive type. But they provide more torque application in the attachment. And also, the slippage is lower if we compare it with the straight slot type.
Straight Slot Drive Type
This is the most common type of drive in most of the screws. We can use flat and straight drivers or drill bits to attach and detach these drive types. Also, attachments of drives are very simple with the straight slot type.
This is also another drive type for set screws to allow more torque applications. This type has a star-like shape which provides better application of torque. Also, the attachment of the bit is much easier. For industrial screws, 6-point or 8-point splines are better for attachment and detachment.
Applications of Set Screws
Actually, around the applications of these screws, the extra tightening force between the hubs and shafts. Because the movements are generally possible between these mechanical elements. To prevent it, we use set screw mechanisms.
We use different kinds of set screws for different applications. For example for bigger and semi-permanent applications such as power plants or ship engine transmissions, we use cone-shaped or other interference screws.
But for smaller applications, we use flat and plain types of screws in general.
Advantages and Disadvantages of Set Screws
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Like the other machine elements, there are advantages and disadvantages of set screws. We need to consider them while we are applying them in our applications.
- The most important advantage of them is they provide an additional assembly force. So, this is very important for relative motion between the shaft and hub.
- They are very easy to detach and attach. You can easily detach by using drivers and you can take the parts easily. Because of this, the maintenance is very simple.
- There are different types of set screws. So, you can use these screws in different sizes of applications.
- The most important disadvantage is they can cause scratching of shafts or other elements which will result in a decrement in the mechanical strength.
- Loosening is a problematic issue for these screws. If they loosen, they cause big accidents. Because of this issue, some types of set screws are prohibited in different countries.
- They add additional costs up to the design. Because you need a threaded hole and an additional screw in the design.
So, set screws are very important mechanical parts. There are different types of them to use for different purposes. Also, it is very important to know their general standards of them. Because we are creating our designs according to the standards.
There are different kinds of applications in which we use set screws. And also, we need to consider the advantages and disadvantages of their use in our applications.
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FAQs About Set Screws
They are the screws that we use to prevent the rotational motion between shafts and hubs. Also, we use them in applications where there is a rotational and axial motion. They provide additional preventing force for them.
It is very simple. You just need to use screwdrivers or drive bits. Attach the screw drive or drive a bit on the head of the screw, and rotate clockwise to tighten. And rotate counterclockwise to loosen.
No, they are not. There are different sizes and standards of them. We can use these standards in different kinds of screwing applications. These standards are defined according to the American and Metric standards.
If there is a loosening problem for set screws in an application, you need to consider other mechanically strong types such as cone types and dog types. Check the article above.
In general, there are 8 different types of set screws; Ball-point, soft-tipped, dog-point, cone tip, oval tipped, flat type, knurled tip, and plain type. They have different kinds of features. You can find the detailed information above.