Pin connections - Connecting components with cylinder pins - methods / errors

In this article, we will focus in detail on the subject of pin connections in the mechanical field. We will take a close look at molded parts such as bolts and pins, as well as other fasteners and securing elements and their decisive role in pin connections. We will discuss different examples of pin connections and potential defects when pinning components.

What is a pin connection?

Pin connections and bolt connections are a subset of interlocking connections and appear to work the same at first glance. Although both types of joints are detachable and resemble each other visually, they differ in their mode of action. Whereas pin connections are understood to be a friction-locking, fixed connection, bolt connections generally provide an inter-locking, loose connection. However, the operating principle is the same. A bore hole is created by one or more components that are connected to one another. A pin or a Knuckle Pin is inserted through this bore.

For example, when an oversized cylinder pin is pressed into the bore, a so-called friction-locking or fixed connection is created. Such a pinned connection holds the components together by the mechanical friction and the pressure between the pin and the corresponding bore holes. Force is thus transmitted by producing a stable, friction-locking contact between the components and the connecting element. Bolts are often used for interlocking or loose pin connections. In order to prevent the bolts from coming loose due to loads during operation, locking elements are required for axial securing.

Pin connections are used in various applications. These fixed connections are very common in mechanical engineering. Components are securely connected to one another by selecting a fixed fit.

Bolt connections are used to secure a position by creating an interlocking joint. This connection is characterized in that the connection can be non-destructively loosened in the load-free case by loosening the locking element, for example in order to locate workpieces on machine tables or devices in order to keep them stable during the machining process or for rotary movements.

What are some examples of pin connections?

In the area of mechanical connections, pins and bolts play a central role and are used in a variety of ways. The following pin connection examples list the connections most commonly used in mechanical engineering and design. Each of these joint has unique features and characteristics that enable a secure connection of components and optimal force transfer. In the following sections, we will provide a brief review to bolt connections and will then focus on pinned connections.

Bolts

Bolts are interlocking connections that can be loosened non-destructively. To ensure that the connection is not loosened during operation, there are various versions of bolts to secure them.

• (1) - Locating bolt
• (2) - Hinge bolt with two-sided ring groove
• (3) - Bolt with cotter pin hole
• (4) - Threaded bolts

Bolts are connecting elements that are used to create loose or also articulated connections. To avoid unintentional loosening of the bolts, they are used in conjunction with retaining elements such as Retaining Washers, retaining rings, Spring cotter pins or split pins.

Cylinder pins

As the name suggests, cylinder pins are cylindrically shaped connecting elements. As a rule, the ends of Cylinder Pins are usually rounded or beveled.

• (1) - Cylinder Pin - beveled on both sides
• (2) - Conical pin - rounded with internal thread
• (3) - Grooved Pin
• (4) - Spring pin
• (5) - Heavy-duty tension pin

Cylindrical pins are used to connect and secure components.

Depending on the production specification of the bore hole, cylindrical pins have a fit tolerance that ranges from an easily detachable connection up to a difficult-to-release connection. Easily detachable connections are used in assembly jigs, while difficult-to-release connections are used for the permanent connection of components.

Dowel pins require precise fit tolerances to fulfill their respective function. As a rule, dowel pins are oversized and are pressed into the receiving bore extending through all parts to be connected under the influence of force. Depending on the fit tolerance, these connections can be designed such that they are either easily detachable or are permanent by a defined interference fit of the dowel pins into the receiving bore. Easily detachable dowel pin connections are particularly suitable for applications where frequent adjustments or maintenance are required. However, such connections are generally not vibration-proof. Some dowel pins have an internal thread. Cylindrical pins with internal threads are usually used where it is not possible to damage the dowel pin. For example, if the pin is recessed in a blind hole, the internal thread allows easier disassembly with a pull-off tool or a pull-off screw.

Another important feature is the hardness of the material - hardened or unhardened. The hardness is directly related to the loads. In principle, the pin should be made of a harder material than the parts to be connected. If the load on the pin is high, a longitudinal groove for pressure relief can also be provided.

Conical pins

Conical pins owe the name to their unique shape. Conical pins are conical fasteners that fit into corresponding bore holes and hold machine parts together in releasable connections.

The corresponding bore holes must also be opened up on conical pins. Conical pins are easy to loosen and are therefore suited for repeated assembly and disassembly. Due to their conical shape conical pins can compensate for the wear & tear or expansion of the boreholes resulting from frequent assembly and disassembly. Conical pins are capable of absorbing high axial loads and torques, making them suitable for applications with high loads. Conical pins are not vibration-proof. Versions with internal threads or threaded pin are also available for applications where it is not possible to knock out the taper pin.

Grooved Pins

Grooved Pins have grooves or notches that project a bulge on both sides. This grooved bulge is elastically forced into the groove when the Grooved Pin is tapped into a bore hole with a matching tolerance class.

The resulting radial tension of the Grooved Pin against the wall of the bore hole not only ensures a secure, vibration-proof hold of the pin, but also permits trapped air to escape. Grooved Pin can also be reused after loosening without losing the stable hold. When matching the component and Grooved Pin, the material hardnesses and tolerances must be observed:

• The strength of the Grooved Pin must be higher than the strength of the component to be joined. Otherwise, the bulge is not elastically deformed during joining, but is instead removed. This causes the connection to weaken enormously.
• The tolerance of the bore hole must be matched to the connection as a fit tolerance. The bore hole is drilled with a fit tolerance drill.

Tension pins (spring pins)

Tension pins, or spring pins, are short cylindrical pins that are tensioned by their spring action after placement in a bore hole.

The connection with Tension Pins has the following advantages due to the elastic properties:

• The requirements on the wall of the bore hole are lower and the fit tolerances are greater
• The connection can be non-destructively detached and is therefore reusable
• Installation is easy

If you would like to learn more about spring pins, click here.

How to make a pin connection?

The assembly of pin connections requires precision and care. All framework conditions such as component strength, temperature range, expected load, etc. should be known to ensure that the components are correctly aligned and securely connected to each other. It is important to select matching pins or bolts, bore diameters, and mounting methods to ensure a secure and reliable connection. However, the exact steps may vary depending on the specific requirements of your application. You must also ensure that the applicable standards and regulations are followed for your specific application.

In order to establish a pin connection between components, a bore hole is required for receiving the pin or the bolt. The pin or bolt is inserted through this bore. This creates a friction-locking or interlocking connection. The following example steps are used to demonstrate the production of a friction-locking pin connection of a cylinder pin into a blind hole:

• Align components: Make sure that the parts to be connected to each other are correctly positioned and aligned. Check the tolerances and dimensions to ensure that the pins fit properly.
• Drill holes: Drill the appropriate holes in all components. The bore holes must be precisely positioned and adjusted such that the bore hole is undersized in relation to the diameter of the pin. The undersize must be adjusted to the connection according to an interference fit. Use a drill bit that is suitable for the desired diameter. After drilling, accordingly hone the holes for the pin to be used.
• Clean holes: Remove any drill dust or dirt from the drilled holes to ensure that the pins are easily pushed in and have a good fit. Various accessories, such as brushes or blowers, are recommended for cleaning the drill holes.
• Insert cylinder pin: Insert the pin into the drill holes of the components to be connected. Depending on the application, it may also be necessary to first drive the pin into a component and then place the second component on the pin and align it accordingly. The installation of pins usually requires only simple tools such as a hammer or a press. They can be easily tapped or pressed into the pre-drilled holes. Depending on the ambient condition, heat is also used for large interference fits. By cooling the pin or heating the component, the material contracts or expands, which facilitates the joining process.
• Check connection: Check the connection for accuracy and stability. Make sure that the components are firmly connected to each other and do not loosen easily. In many cases, the fit tolerance and friction between the components and the dowel pins is sufficient to secure the connection. As additional safety margin, one can use retaining elements, such as Retaining Washers, retaining rings, Spring cotter pin or split pins as required.

Errors when doweling components

When making pin connections, various defects can occur that can impair the quality and integrity of the connection. Incorrectly pinned connections can also cause poor fit and possible misalignments. In order to avoid such errors and the resulting risks, careful planning, accurate machining, appropriate quality control and regular maintenance are required. Here are some common errors:

• Faulty design: An inadequate design or dimensioning of the pin connection can lead to problems, especially if it cannot withstand the forces and loads of the application. If the pin connection is overloaded, this can lead to deformations, fractures or premature fatigue of the components.
• Improper fit tolerance: If the bore holes and pins or bolts do not have the correct tolerances and fit tolerances, this can lead to an insufficient connection. For example, an overly tight fit tolerance can cause overload and breakage, while an overly loose fit tolerance can impair the stability of the connection.
• Material properties: If the pins and bolts are made of inferior material or do not meet the requirements of the application, this can lead to premature fatigue or breakage.
• Dirt or corrosion: Dirt, dust, or corrosion in the bore holes or on the pins and bolts can negatively affect friction and fit tolerance.
• Improper maintenance: Unmaintained or improperly maintained releasable pin joints can lose quality over time and increase the risk of failure.

Is a pin connection detachable?

A pin connection can be loosened in various ways. When selecting the method for loosening the connection, the type and size of the pin or bolt, the type of lock and the specific construction must be taken into account. Screw pullers or puller tools are special tools used to remove pins, bolts, or other fasteners that are firmly seated in bore holes. They are simple and efficient tools to remove fasteners without damaging the fastener and surrounding components.