What Is a Spring Pin?
A spring pin is a hollow pin made by bending a thin plate into a cylindrical shape and applying a mortise (slit process) to it to form a C-shaped cross-section.
Because it is hollow, it is lighter than a solid pin. It is inserted into a hole, with a hole diameter slightly smaller than the pin’s outer diameter, and used to fix or constrain rotation by spring force as the pin expands outward.
Generally, it is also used synonymously with a rolling pin, tension pin, etc.
Use of Spring Pins
Spring pins are used for locating, preventing rotation, and retaining parts. Since the spring force of the pin acts to secure the part, high hole diameter accuracy is not required. The pin can be adequately secured in drilled holes without reaming. Therefore, it is easier to use than solid parallel pins or tapered pins. The spring force also makes them less likely to drop out against vibration.
There are two main types of springs, one for general use (straight) and the other for light-load use (corrugated), which are used according to their respective characteristics.
The general-use springs are used for simple fastening and positioning. Slits are available in straight and corrugated types, and both ends are tapered or R-processed to facilitate insertion into holes.
The light-load type is a simpler type of fastening that requires less load to insert than the general type. This is used for lightweight materials such as aluminum and resin that do not require high strength. Slits are corrugated and less prone to tangling, making them suitable for automatic insertion.
Spring Pin Types
Refer to the figure below for an example of spring pin use (fastening of shaft and pinion gear to prevent rotation).
Cable gland, refer to the following for an example of spring pin selection.
- Pin O.D.: Select a pin based on the combination of the pin diameter and hole diameter listed in the dimension tables of the respective manufacturer.
- Pin strength: Confirm that the pin meets the shear load specified in each manufacturer’s dimensional table.
Principle of spring pins
The main feature of spring pins is that they can be inserted into a machined hole with a hole diameter slightly smaller than the pin’s outer diameter. They can be fixed or rotationally restrained by the spring force that causes the pin to spread outward. Therefore, high-precision hole diameters are not required, and finishing processes such as reaming can be omitted. The pins can then be used as drilled holes, resulting in fewer processes and lower manufacturing costs.
However, they have lower shear strength than solid parallel pins and tapered pins and are not suitable for high load and high precision fasteners. If more strength is required, two pins with different outer diameters can be used in combination.
Care should be taken when using this method because the pin can easily come loose if vibrations occur in a direction parallel to the pin’s axial direction. Also, if the fastener is repeatedly rotated, the pin will easily come loose, so care is required.
To insert a spring pin, lightly tap the end face of the pin with a hammer or the like. If the spring pin is difficult to insert, slightly increase the hole diameter for fine adjustment. To pull out the spring pin, place a pin punch or similar tool on the end of the pin, tap it lightly with a hammer, etc., and pull it out.