The Difference Between 2nd and 3rd Member Shear in Demolition

Rotating hydraulic shears are heavy-duty attachments for excavators, designed to cut steel beams, pipe and reinforced concrete in demolition and scrap processing. These shears mount in one of two ways on an excavator’s linkage – either as a second-member installation (replacing the stick) or a third-member installation (replacing the bucket). In a second-member setup the shear is pinned where the stick normally attaches to the boom, whereas a third-member shear attaches at the stick’s tip like any bucket or grapple. These mounting choices have distinct effects on machine configuration, reach, transport and capability. In general, smaller machines and high-reach tasks favor third-member mounts, while very large excavators with heavy shears often use second-member mounting. Understanding the differences – and the trade-offs of each – is critical when choosing the right demolition shear for your project.

What Are 2nd Member and 3rd Member Shears?

In demolition terminology, “2nd member” and “3rd member” refer to which pivot point on the excavator the shear replaces. A second-member shear is mounted on the boom in place of the excavator’s stick (dipper). This means the machine’s boom is fitted with a special bracket or link at the boom pivot (the “second member”) and the normal stick is removed. The shear’s head and hydraulic cylinder then attach at that point. By contrast, a third-member shear is attached at the end of the stick – essentially where the bucket would go. In practice, a third-member shear uses a quick-coupler or pin connection on the stick tip (the “third member”), just as a bucket or grapple would. This allows the excavator’s boom and an auxiliary stick bracket to carry the shear, while the original stick (or a short hitch) remains in place.

These mounting configurations have practical implications.Shears “can be mounted on a multitude of carriers, from skid steers to a PC1250,” and that the excavator’s size generally determines whether a 2nd or 3rd member mount is used. In other words, smaller excavators typically handle third-member attachments (swapping out the bucket), whereas very large demolition machines can install a fixed second-member bracket to carry a much larger shear. The choice affects how far and high the shear can reach, how much weight the excavator can carry, and even how the machine can be used (or not) for other tasks.

Second-Member Shears: Configuration and Capabilities

Image: A large second-member demolition shear (with stock jaws) mounted in place of an excavator’s stick. Such shears are built for maximum cutting force and jaw opening.

A second-member shear is fixed to the boom of the excavator. The machine’s normal stick (dipper) is removed and a heavy bracket is pinned at the boom pivot, making the shear essentially part of the boom assembly. This configuration allows a very large, heavy shear to be mounted, because the excavator’s full lifting capacity can support it. Shears in the second-member position often have larger jaw openings, bigger cylinders and more robust frames than comparably sized third-member shears. Because the bucket and stick are gone, the mass of the shear is carried by the main boom, so the carrier can run the heaviest possible attachment it can handle. For example, a huge jump in recommended excavator size when switching from 2nd to 3rd member for the same shear model.

Use Cases. Second-member shears excel in scrap yard processing and secondary demolition. In these scenarios the shear is often cutting heavy steel rails, beams and machines at or near ground level. The priority is maximum cutting power and cycle speed, not reach. With the stick removed, the machine sacrifices overhead clearance but gains cutting force. The stability and weight support of a boom-mounted (2nd member) shear makes it ideal for consistently munching through dense loads of metal. “scrap yards and secondary demolition use 2nd member shears”, reflecting this common practice. In practical terms, a scrap yard customer might mount a massive shear on a 50-ton excavator in 2nd-member mode to feed processed metal directly into a rail or barge.

Advantages of 2nd Member Shears:

• Allows much larger, more powerful jaws because the shear’s weight is carried by the boom. This means thicker steel and larger sections can be cut in fewer strokes.

• High cutting force and cycle speed are possible, since the excavator can use maximum hydraulic flow and the shear’s geometry can be optimized for strength.

• High stability on large carriers: with the stick gone, the shear’s center of gravity is closer to the base, lowering risk of tipping on a heavy machine.

• Shorter attachment length: because the shear is boom-mounted, the shear’s jaws are closer to the base, which can improve lift capacity for heavy loads compared to a long stick setup.

Limitations of 2nd Member Shears:

• Dedicated machine usage: The excavator’s stick is removed, so the machine cannot quickly switch to buckets, grapples or other tools without reattaching a stick. The excavator is effectively dedicated to shear work.

• Increased transport length: Removing the stick and adding a fixed bracket often makes the machine + shear longer. This can make transporting the machine more involved, requiring special rigging or multiple transports.

• Height restrictions: With the shear on the boom, overall machine height may increase. Some very large 2nd-member setups are too tall to fit under low overpasses or inside confined sites. As one contractor noted, very large equipment is “hard to get in and out of small yards… They’re tall. You get some bridge problems.”.

• High installation effort: Setting up a 2nd-member shear usually requires removing the standard stick and rigging in a heavy mounting bracket. This process takes time and often a specialized technician or rig.

• Cost and availability: Second-member shear kits (the shear plus mounting bracket) tend to be expensive and custom-fit to each carrier. According to ShearForce, 2nd-member mounts are “more expensive and dedicated to a specific machine model.”. In other words, you may need one shear per machine, and it’s not as easy to share across fleets.

Third-Member Shears: Configuration and Capabilities

Image: An excavator dismantling a building with a third-member shear. The shear is attached at the end of the stick, giving extra reach (and leaving the boom free). Such shears trade some size for reach and flexibility.

Third-member shears are mounted in place of the bucket on the excavator’s stick. In practice, the shear is pinned or coupled to the stick tip, exactly where you would normally attach a bucket or grapple. The machine’s boom and existing stick remain in place (often with a short hitch cylinder), and the shear is an “extra” tool hanging on the stick – hence the term third member. This gives the excavator additional reach: effectively the full length of the boom plus the stick can be used, and some setups even have telescoping sticks for even more height. The trade-off is that the shear must be smaller or lighter so that the stick can lift it.

Third-member installations offer great flexibility. Since the original bucket and stick are only removed, and no permanent bracket is needed at the boom, the excavator can more easily switch tools. As one scrap yard operator observed, with a third-member shear “we’re able to switch over to a third-member shear… then go back to the bucket and thumb for loading… they’re pretty versatile.”. In practical terms, this means the same excavator can alternate between shear work and other tasks (like material handling) with minimal downtime. For primary demolition of structures – for example, “decommissioning buildings, bridges or other structures” – third-member shears are preferred. The longer reach lets operators work several stories up without needing a special high-reach excavator boom.

Advantages of 3rd Member Shears:

• Extended reach: Because the shear is at the stick end, it can reach higher or farther into a structure. This is critical for high-reach demolition or when working on multi-story buildings.

• Machine versatility: The main boom and stick remain intact, so the machine can still use its bucket, grapple or thumb after removing the shear. You’re not locked into one tool. 3rd-member machines “will not be dedicated to only running the shear” – they can switch back to other attachments.

• Availability and lower cost: Third-member shear mounts (often just quick-coupler or simple adapter) are more universal. As ShearForce states, 3rd-member shears have the advantage of “availability” because they are less machine-specific. In practice, rental or resale of third-member shears is easier, and one shear can often be fitted to multiple machines of similar size.

• Easier transport of machine: Since many third-member shears are on mid-sized carriers, the overall height may be lower than a mega shear setup. In the Marshfield Scrap example, the operator chose a smaller excavator and shear because it “was fairly easy to move around” compared to a larger, taller rig. It could fit on any lowboy trailer and even go under bridges more easily.

Limitations of 3rd Member Shears:

• Smaller shear capacity: Third-member shears must be light enough for the stick to lift, so their jaw opening and force are generally less than a comparable second-member shear on the same base machine. If you need maximum bite on very thick steel, a third-member shear might reach its limits.

• Requires large carrier or strong hydraulics: To maintain capacity, a third-member shear might need a bigger excavator than a second-member setup of similar cutter size. Many third-member shears require two auxiliary hydraulic circuits (one for jaw operation and one for continuous rotation) and sometimes a case drain. You must confirm your excavator has the flow, pressure, and plumbing for the rotating head.

• Additional mounting hardware: Although simpler than a fixed boom bracket, third-member installation still usually requires a specialized adapter or hitch on the stick. Some shears use a reusable coupler plate; others may need a welded plate. This adds a bit of complexity to installation and ensures the shear’s pins match the stick.

• More limited stability: Because the shear weight is farther out, it can induce more stick deflection under heavy loads. High end third-member shears include reinforcement in the shear stick (as ShearForce mentions) to minimize “buckling” under load. But fundamentally, a third-member shear has a smaller safety margin against bending or swing forces compared to a second-member mounting.

Key Factors: Reach, Power, and Use Cases

Whether 2nd- or 3rd-member mounting is best depends on the project’s demands. A few key considerations include:

• Job Type (Primary vs. Secondary Demolition): For primary demolition (taking down structures at the site of construction), reach and flexibility are often top priority. Third-member shears are typically used, because buildings require cutting at height and the ability to maneuver around structures. In secondary demolition or scrap processing (work done after materials have been brought to ground level or a processing yard), maximum cutting force and cycle speed can be more important. Second-member shears often shine here. For example, a bridge or warehouse demolition might use 3rd-member shears to cut beams on upper floors, whereas a scrap yard’s steel processing is usually done with 2nd-member shears on heavy carriers.

• Machine Reach and Height: If you need to reach tall heights or far into a building, third-member is the answer. Conversely, if reach is not needed (e.g. you’re at ground or floor level), a second-member shear can focus on power. As noted, third-member mounts significantly extend reach because you’re effectively adding the stick length on top of the boom. Also consider site clearance: very tall second-member installations may conflict with overhead obstacles, whereas a third-member machine (especially if it’s a smaller carrier) can sometimes move into tighter spaces.

• Excavator Size and Transport: The excavator’s weight class is critical. ShearForce’s rental guide cautions that 2nd-member shears at the limits of an excavator’s weight or any 3rd-member shear requires pre-approval by the manufacturer. In practice, ensure your carrier can handle the shear+bracket weight. A smaller excavator (e.g. 20–30 ton) might only carry a small third-member shear safely, whereas a 50–80 ton machine might be needed for a large second-member shear. Transport considerations also matter: smaller, low-profile machines (often with 3rd-member shears) can load on a standard lowboy easily, but the largest machines and shears may need special oversize handling. As one contractor observed, “moving those [large] things around is a lot more difficult” in tight yards. A more compact setup (often third-member) allows easier mobility between sites.

• Transport and Installation Logistics: Consider how you’ll move and set up the equipment. Second-member kits are heavy and bulky; installation typically involves a truck crane or rig to remove/attach the excavator stick and shear bracket. Third-member shears usually install via a quick-coupler or pinning the stick’s end – a simpler procedure, often doable with the machine’s own hydraulics or a small crane. Also, think about whether the machine’s swing angle or short-turn-radius (e.g. short rear overhang) might limit using a long shear.

• Availability and Cost: If you’re renting or budgeting, third-member shears tend to be more common. Rental companies report that “the vast majority of hydraulic shear rentals are 3rd member setups”. Third-member shears are generally more interchangeable between machines. Second-member shears, by contrast, often require a dedicated carrier and bracket, which can drive up the cost per job. ShearForce explicitly notes that “mounts of 2nd member shears are more expensive and dedicated to a specific machine model”. In short, a third-member shear can often be a one-size-fits-many solution, whereas second-member systems are special builds.

• Equipment Versatility: If you need your excavator to do more than just shear, a third-member solution is less limiting. You can pop the shear on for demolition cuts, then go back to a bucket, magnet, or grapple for other tasks without complex reconfiguration. Second-member machines usually sit idle when not shearing (since the stick is gone), so they require renting or owning a separate carrier for other work.

• Maintenance and Parts: Mechanically, both types of shears require similar maintenance on blades and hydraulic components. However, because second-member shears are larger, they may have more wear parts. On the other hand, a third-member shear’s extra hydraulic lines and rotator may add some maintenance tasks. Plan for spare wear tips and blades for the shear regardless of mounting.

Advantages and Limitations Summary

In summary, second- and third-member shears each have their strengths:

• Second-Member Shear (Boom-Mounted)

  • Advantages: Accommodates the largest jaw openings and highest cutting force on a given carrier. Excellent for mass-processing steel in scrap yards or recycling. Maximizes power for metal feeding.

  • Limitations: Requires dedicating the excavator to shearing (stick removed), more complicated installation, and larger transport profile. Generally limited to the very largest carriers. Less flexibility for non-shearing work.

• Third-Member Shear (Stick/Quick-Coupler Mounted)

  • Advantages: Provides extended reach and height for high or hard-to-reach demolition. Allows the excavator to still use a bucket/thumb or other attachment quickly. Easier to share among machines (more common mount system) and quicker to transport and set up.

  • Limitations: Shear size and cutting force are smaller for a given machine. Requires dual hydraulic circuits and careful match with machine weight. Stick deflection and stability can be higher under load.

Ultimately, the choice depends on your application. If you need to slice very thick steel or make very fast cycles on ground-level demolition (as in a scrap yard or pipe yard), a second-member shear on the biggest excavator possible will give you that raw power. If you need to dismantle a tall structure, process bridge girders, or you want the excavator to do multiple tasks, a third-member shear is more appropriate.

Choosing the Right Shear Configuration

When selecting a shear, consider the following practical points:

1. Excavator Weight Class: Check manufacturer specifications. Many shears list separate recommended carrier weights for 2nd- vs 3rd-member installation. For example, LaBounty shows that one shear model might need a 26–40 tonne excavator in 2nd-member mode but an 88–110 tonne carrier for the same shear in 3rd-member mode. Always verify that your carrier is within the safe range for the intended mounting.

2. Site Accessibility: Can the machine reach the work area easily? If site access is tight (low bridges, small yards), a lower-profile third-member setup on a smaller machine may be preferred. Conversely, if height isn’t an issue and maximum power is needed at ground level, a heavy second-member arrangement might be fine.

3. Hydraulic Supply: Make sure your excavator has the required hydraulic circuits. Most third-member shears need two high-flow aux circuits (one for shear open/close, one for rotation) plus a case drain. If you only have one auxiliary circuit, you may be limited to fixed shears or need additional flow valves. A second-member shear typically only needs one high-flow circuit (for the jaw) since the stick’s own cylinder drives rotation if integrated.

4. Budget and Utilization: Evaluate how often the shear will be used. A second-member shear and its custom mount can be a significant investment, so it makes sense if you will use it frequently on large jobs. If you only occasionally need shearing, renting a third-member shear (or using an existing one) might be more economical. Also consider the cost of lost time if a machine is tied up as a single-use shear carrier.

5. Versatility Needs: If you want the machine to handle concrete, debris sorting, or loading trucks when not shearing, third-member is more flexible. If the excavation task is solely demolition of a steel structure, dedicating a machine with a second-member shear could be justified.

6. Physical Handling: Keep in mind that the shear itself is heavy. Transporting a second-member shear often means transporting the whole excavator (or using on-board crane features) to install it. Third-member shears can sometimes be carried in the excavator’s bucket or lifted by a small boom for quick swaps.

By reviewing the project specifics and matching them to these factors, buyers can determine the best configuration. For instance, a contractor breaking up a bridge span into a scrap yard would likely use a large second-member shear (favoring shear size over reach), while a contractor dismantling a high-rise steel frame would choose a third-member shear for the needed outreach and flexibility.

Conclusion

Choosing between a 2nd-member and 3rd-member hydraulic shear is a key decision in planning demolition work. Second-member (boom-mounted) shears deliver the greatest cutting force and are common in scrap and secondary demolition, while third-member (stick-mounted) shears offer extended reach and machine versatility, making them ideal for primary structural demolition. Each has trade-offs in terms of machine setup, installation, transport and cost.

RSBM’s demolition attachment specialists can help match the right shear configuration to your excavator and application. By considering factors like reach requirements, material thickness, excavator size, and on-site logistics, you can select the shear setup that maximizes productivity and efficiency. Whether you need a heavy-duty boom-mounted shear for processing giant steel members or a high-reach stick-mounted shear for top-down building take-downs, understanding these differences will guide you to the optimal choice for your demolition project