Knuckle Boom Cranes and their Importance in Construction Industry

knuckle boom crane

What are knuckle boom cranes?

Knuckle boom cranes have an articulating arm and two booms that allow them to not only move materials in a telescopic motion but also bend like a knuckle to go over and around other objects at various angles.

Then when the work is completed, the knuckle boom crane folds down into a compact form that does not take up much room on the truck.

Important uses of knuckle boom cranes

Civil construction projects rely on heavy construction equipment for digging, lifting, and grading tasks. One piece of vital equipment used for residential and commercial construction is a knuckle boom crane. Knuckle boom cranes are typically mounted on vehicles yet may also be mounted on boats and trains.

Using these types of equipment provides operators with additional ways to complete a project in a safe and proficient manner. The knuckle boom cranes are extremely mobile. They are lightweight to be placed on the truck as the set-up is fast and it does not take up much space.

knuckle boom crane lifting operation

What are their attachments?

They come with a range of different attachments such as buckets, pallet hooks, grapple saws, grabbers, and others. These machines also come in varying sizes from 3.5 tons/MT up to 350 tons/Mt. Yet one of the top benefits is its versatility. Not only can it lift objects horizontally and vertically, but also be downward at a slant when mounted on the rear of the truck.

This allows the knuckle boom to lower materials down a flight of stairs when constructing or expanding underground garages or for subway projects. When vertical clearance is limited, these machines excel when loading and unloading materials.

A knuckle boom crane can take the place of other heavy equipment for construction jobs. If requiring roofing materials, HVAC systems, or other objects to be lifted in tight spaces, a knuckle boom can be used instead of an excavator or backhoe loader. The knuckle boom cranes fit in places that may restrict excavating cranes and can reach higher than backhoe loaders. Wherever a truck fits, so too does the knuckle boom crane.

What is the other importance of knuckle boom cranes?

Another important factor is its cost savings. These attachments are much cheaper than other heavy equipment, as you are only purchasing the booms, hydraulics, controls, and attachments. You are not purchasing the cab, engine, or tracks as you would an excavator, skid steer, or track loader. The knuckle boom crane is detachable from the truck, so you can upgrade to a larger model of knuckle boom crane while using the same truck. On the other hand, when it comes time to replace the truck, you simply attach the same knuckle boom crane to the new truck. 

When it comes to constructing buildings, bridges, structural foundations, roadways, or residential homes, knuckle boom cranes can handle large and small jobs efficiently with similar load capacities as other heavy equipment.

Consider using these machines for your next civil construction project.

Small Knuckle Boom Crane

There are multiple cylinders within the small knuckle boom crane. Its components are usually constructed of high-durability and strength steel of rectangular shape.

It is the element in the control of holding and modifying the position of the load manipulating components.

It is the most frequently requested component because it is in charge of resisting the majority of the efforts generated by the loads handled. It is made up of four 11-meter-long components that are assembled inside each other in such a way that they may move to change the length arrangement.

It has all of the components needed to change its length or extension.
Profiles of the boom are determined by the bending, torsion, and compression efforts they are subjected to as well as by the mechanical properties of the materials they are manufactured from.

Mechanism of a rear-mounted knuckle crane truck

The material utilized in the boom’s sections is high mechanical resistance steel.

The pen is subjected to a tremendous degree of effort, hence this type of material is used such when:

  • The flexion occurs when handling a weight that is positioned at a given distance from the boom’s anchor.
  • The torsion is created by the load when the wind impinges on it, as well as the torsional stress that causes the acceleration of the load positioned at a specific distance.

This type of material will allow the thickness of the sheet used to make the profiles to be reduced, resulting in a significant reduction in the boom’s weight.

The crane’s key components

Roller Skates

The skids are parts that allow the inner portions to slide, decreasing friction and creating a contact surface that allows the manipulated loads’ efforts to be distributed more evenly.

They are situated near the profile’s rounded corners. Skates are perfect for working on hard metal surfaces.

Each segment includes eight runners, which are divided so that four skates are on the back of the boom and four skates are on the front.

Its geometry is based on the cross-section of the gap between two sections, which is 20 mm thick. They have a step that will be used to fix the skates on both the rear and front of the skates that contain the pen.

M16 screws will be used to secure the runners. The screws that will link the skates and the coverings will pass through holes in both.

The skates will be attached to the inner profile at the back of the boom, allowing them to move along the portion that you want to extend, while the skates will be fixed to the outer profile at the front, allowing them to remain fixed.

The Skates’ Material

Skates made of polyamide will be utilized, which have the following advantages:

They do not require lubrication: The material contains solid lubricants that are linked to the molecular structure, ensuring the presence of lubricant throughout the piece’s useful life. As a result, they are appropriate for regions with limited access or where lubrication is an issue.

Easy and smooth movement: Because they have no stick-slip effect (the stick-slip effect, also known as the oscillation phenomena due to relaxation, is the spontaneous spasmodic movement that can occur as two objects slide over each other), the movement begins smoothly and in a regulated manner. (This is a necessary feature for machinery that is designed to lift or transport objects.)

Excellent wear resistance: They endure far longer than other substitutes even without lubrication.

Good load capacity: The load is distributed more evenly by giving a large contact surface.

corrosion-resistant: it’s a good choice for external use, including in marine conditions. Additionally, the internal lubricant that they include protects the area of the pen where they glide.

Rear Coverings

At the back ends of the profiles, 200 mm thick plugs are welded, with the purpose of housing the anchor bolts between sections in the upper part, which will allow the boom’s sections to be joined together, as well as locating two holes, one in each lateral, from which the telescoping system will drag the sections to carry out the boom’s total or partial extension.

The central hole in the upper part, where the anchor bolt will be positioned, can be distinguished from the lateral holes in the square section, which will accommodate the section’s drag bolts.

Its interior geometry is the same as the telescoping body’s, allowing it to fit exactly while also serving as a support base.

In order to combine both the upper anchor bolt and a spring that will prevent the bolt from being displaced from its operational position, there is a vacuum of material between the exterior and internal top of the lid.

Front Covers

These pieces will let the skids and skid coverings be screwed together, allowing for a good mechanism.

Skate Housings

To secure the front part’s skids, there are coverings made of steel, with holes positioned in such a way that when assembled, they are concentric with the holes carried by the skids.

By doing so, you can begin assembling the skids and coverings by using M16 screws. There are four casings available, one for each of the four skids that must be installed in the front, two on the top, and two on the bottom.

It was decided to include these features for the sake of resistance, as it is not considered practical to attach the skids with screws directly on the surface.

Feather Head

This component is welded to the last portion of the telescopic boom and is responsible for holding the pulleys at the front end. Its geometry is such that the cable does not come into contact with the pen while tilting, hence it has axes that divide the two pieces.


Knuckle boom cranes are an incredible feat of engineering. They are also known as loader cranes, picker cranes, or articulating cranes, which have revolutionized the way people load and offload in a range of industries.

Dustin Johnson is the marketing manager of FortisHD
About Author
Dustin Johnson is the marketing manager of FortisHD and an enthusiast in construction and heavy equipment. Construction has been an integral part of his life, and he is proud to be able to continue to build his future in such an exciting industry. Throughout his career, he has been fortunate enough to be involved with many engaging projects and is appreciated and valued for his works with the contracting team