Skidder-Mounted Tree Shears and Shop-Built Logging Conversions

[MikePhua]

The Evolution of Skidder-Based Felling Machines
Skidders have long been the backbone of timber extraction, originally designed to drag felled logs from forest to landing. Over time, operators and fabricators began modifying skidders to perform additional tasks—most notably tree felling and bunching. One such innovation is the mounting of tree shears directly onto the front of a skidder, transforming it into a hybrid feller-buncher capable of cutting and piling trees in a single pass.
The concept gained traction in regions where fire risk restricted chainsaw use or where pulpwood harvesting demanded speed over precision. These machines offered a cost-effective alternative to purpose-built feller-bunchers, especially on small or fragmented sites.
Understanding the Tree Shear Configuration
A typical tree shear mounted on a skidder includes:

• Hydraulic shear head with reinforced jaws
  
• Blade made of high-tensile steel, often replaceable
  
• Swing or tilt mechanism for positioning
  
• Hydraulic lines routed from the skidder’s auxiliary ports
  
• Stabilizer arms or guards added to the front frame
  

Terminology Note: “Feller-buncher” refers to a machine that cuts and gathers trees before depositing them in bunches. “Shear head” is a cutting attachment that slices through trunks using hydraulic force rather than a saw.
In one notable example, a 518G skidder was retrofitted with a shear head and reoriented cab, allowing the operator to face the cutting direction. The machine’s forward travel was reversed, steering was adapted, and the grapple boom remained intact for post-cut handling.
Advantages and Limitations of Shear-Based Felling
Benefits of shear-mounted skidders include:

• Reduced fire risk compared to saw-based heads
  
• Ability to pile trees immediately after cutting
  
• Lower operating cost and maintenance compared to saw systems
  
• Simplified hydraulic setup using existing skidder circuits
  
• Ideal for juniper, pine, and pulpwood species
  

Limitations:

• Shears may split or crush sawlogs, reducing timber value
  
• Limited precision compared to disc saw or bar saw heads
  
• Slower cycle time on hardwoods or large-diameter trees
  
• Cab orientation and visibility challenges in retrofitted units
  
• Hydraulic flow constraints if skidder pump is undersized
  

A forestry crew in Arizona used a shear-equipped skidder to clear juniper for fire mitigation. The machine’s ability to cut and pile simultaneously reduced labor by 40%, though some logs showed end splitting unsuitable for milling.
Shop-Built Conversions and Field Engineering
Many shear-equipped skidders are not factory-built but rather shop-fabricated by skilled mechanics. These conversions often involve:

• Reversing cab orientation and steering linkages
  
• Reinforcing frame and mounting points with gussets
  
• Installing hydraulic diverter valves and flow regulators
  
• Adding guarding to protect hoses and cylinders
  
• Custom-fabricating brackets and shear mounts
  

Challenges include:

• Lack of documentation or schematics
  
• Difficulty sourcing replacement parts for shear heads
  
• Hydraulic troubleshooting without factory flow charts
  
• Balancing weight distribution after cab reversal
  

Solutions:

• Collaborate with hydraulic specialists to map flow paths
  
• Use pressure gauges to diagnose shear actuation issues
  
• Retrofit modern control valves with adjustable flow settings
  
• Maintain a log of modifications and part numbers for future service
  

In 2023, a logger in Tennessee rebuilt a shop-converted shear skidder originally from Washington. After resolving hydraulic deadhead issues and replacing worn seals, the machine returned to service clearing invasive cedar.
Comparing to Purpose-Built Feller-Bunchers
Purpose-built feller-bunchers like Hydroax, Barko, and Tigercat offer:

• High-flow hydraulic systems optimized for cutting heads
  
• Factory-integrated cab orientation and visibility
  
• Reinforced undercarriage and guarding for logging stress
  
• Advanced control systems and joystick ergonomics
  
• Proven reliability and support network
  

However, for small crews or budget-conscious operations, a shear-equipped skidder offers:

• Lower acquisition and operating cost
  
• Easier parts sourcing for base machine
  
• Flexibility to revert to traditional skidding tasks
  
• Simpler mechanical systems for field repair
  

A contractor in Maine used a Clark 45FB conversion for years before upgrading to a Hydroax. While the purpose-built machine offered better speed and durability, the Clark had served reliably with bolt-on guards and a Perkins engine.
Conclusion
Skidder-mounted tree shears represent a creative and practical solution for specific logging environments. Whether shop-built or factory-supported, these machines offer versatility, cost savings, and adaptability—especially in regions focused on pulpwood or fire mitigation. While they may not match the precision or speed of modern feller-bunchers, their value lies in simplicity and ingenuity. In the woods, where terrain and timber vary by the acre, the right tool is often the one you build yourself.