Bushes and pins are known for ages as parts of bigger machines: construction, cars, and other mechanical systems. These are the key components of cranks and other rotating systems.
Most people connect bushes and pins with cars and drive trains – the real variety of applications of said parts is much wider. Such components can be found in many bigger mechanical systems and their presence is usually noticed during some kind of malfunction.
And again: associations with the automotive industry are strong – most people experience their first exposure to terms like "pins” and "bushes” when these parts cause some problems in cars.
On the other hand: these parts are a basic component of many bigger mechanical systems, their quality has a strong impact on the overall performance of said system. Well-manufactured bushes and pins can work for long years without noticing the end user.
So: how these parts are produced and how the CNC technology can increase their quality?
What are the pins and what are their applications?
Pins are cylindrically shaped parts of a vast variety of lengths and diameters – usually made of steel, aluminum, or brass. These elements are usually manufactured with some type of locking system – eg. head, nose, clamp, or pinhole.
Pins can be manufactured also from polymers and such parts are used in bigger mechanical systems with lower torque and other applications that do not require high mechanical performance. The pin itself is a part of the pin joint and the main role of said system is to transfer crushing or shearing loads from the connected elements.
The other part of the pin joint is bushes – used for object mounting. Pins are usually manufactured on automatic lathes during the external turning process.
Although such parts can be produced in CNC milling machines, the most efficient way is to use the lathe. With the introduction of computer numerical control technology (CNC machines) the pins are currently manufactured mostly on the CNC turning process.
There is a commonly accepted division for:
- headless pins – manufactured as a cylinder, sometimes with beveled ends, usually with additional pin-lock,
- nose pins – with a "nose” on one of the pin ends, similar to the screw head. That type of pins can be manufactured with additional pinholes,
- pins with cylindrical heads – that allow mounting such parts in dedicated holes or bushing. Can be manufactured with additional pinholes,
- pins with threaded stud – the additional threading allows you to mount the pin with a nut or to screw it into a dedicated hole with the right threading and twist ratio.
Pins can be also divided due to application.
The most popular are the piston pins, an important part of an engine crankshaft, mounted in the cylinder liners. Such parts can be used for piston crank mounting and are responsible for the energy transfer from the combustion chamber to the crankshaft. Piston pins are mounted by special springing rings (Seeger rings) that secure parts in place. The pins are manufactured from metal, usually steel, and are subjected to additional processing to improve their mechanical properties.
The most popular type of pins is hardened pins – processed thermally and with higher mechanical rigidity. Such parts are usually machined out of the forged metal block (stainless steel, aluminum) – such material selection provides a better crystal structure of the metal, thus: the lower possibility of mangling or other mechanical damage.
Construction and other parameters of pins regulate international norms, eg. ISO 2340 for headed pins and ISO 2341 for headless.
What are bushings and what are their applications?
Bushings are cylindrical-shaped hollowed parts, often in the form of wider rings. Just like pins, bushings are made usually out of metal (eg. steel, aluminum, copper – especially in applications that require high abrasion resistance), but can be out of polymers (eg. POM).
The main application of bushings is a connection between parts in bigger mechanical systems – such parts are a crucial element of a pin system. The bushing is manufactured in the process of turning (CNC and automatic):
- external – when the part gets its external shape, sometimes with additional indentations (eg. for mounting purposes),
- internal – when the part is hollow and gets its final shape.
There are a few important types of bushing that have unique applications and functions:
- reduction bushings – allow to mount a smaller element in the bigger hole or to increase the Morse grip,
- clamping bushings (also called collets, clamping sleeves) – that allow clamping of other objects thanks to the high gripping force generated by precisely cut arms of the bushing,
- straight bushings – often used in car engines, eg. in cylinder liners.
Pins and bushings production
Contemporary production bushings and pins strongly rely on turning devices like lathes (CNC and automatic). Due to the cylindrical shape of the part, these types of devices provide the best efficiency. The process of turning bushes and pins is relatively simple, but the key elements are
- the right selection of materials,
- the repetitiveness of the whole process,
- lowest possible tolerances of manufactured parts, verified during the quality control.
Just like with other types of machining steel, aluminum, or polymers, the selection of the right material to turn bushings and pins is often more important than the production itself.
The material properties can lead to significant savings during the whole process – on the one hand from the perspective of manufacturing; on the other – for the end user. Although important, such selection requires knowledge in areas like materials science, CNC manufacturing, and others. Just like in other types of machining.
In cooperation with professional bushings and pins manufacturers, you can select the right materials and the process that answers the best for your requirements.
RADMOT - manufacturer of pins and bushings since 40 years
In RADMOT we offer professional CNC milling, CNC turning, and many additional services like aluminum anodization, laser marking, and assembly.
Send us a quote and tell us what type of CNC machined parts you need. We have offered professional CNC services for over 40 years and our quotation is completely free.
If you have any questions regarding CNC manufacturing processes – send us a question: and we will help you to understand it better. Our knowledge is at your service.