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The Kubota KH70 is a compact excavator in the K‑Series family introduced in the late 1990s and early 2000s as a versatile machine for landscaping, small site work, utility installation, and farm use. Kubota Corporation, founded in 1890 in Japan as a cast iron pipe manufacturer, expanded into agricultural and construction equipment in the mid‑20th century and became a global leader in compact machinery. The KH70 was one of Kubota’s key mid‑size models, featuring a robust diesel engine, hydraulic system, and compact footprint ideal for tight spaces. Throughout its production run, thousands of units were sold worldwide. However, many owners find that the factory configuration — typically bucket only — limits versatility. Adding a hydraulic thumb transforms the machine into a far more capable handler of logs, brush, debris, and irregular objects without resorting to makeshift tools.
Hydraulic Thumb Purpose And Terminology
A hydraulic thumb is an auxiliary attachment that works in concert with the excavator’s bucket to grasp objects. Terminology useful in this context includes:
• Hydraulic Thumb — A powered gripper mounted above or beside the bucket that actuates via its own cylinder.
• Auxiliary Hydraulic Circuit — A dedicated line from the excavator’s hydraulic pump and control valve that supplies fluid under pressure to additional attachments like thumbs or grapples.
• Thumb Cylinder — The cylinder on the thumb linkage that opens and closes the thumb.
• Mounting Bracket/Plate — The steel structure that connects the thumb assembly to the excavator’s arm or boom.
• Control Diverter/Flow Control Valve — A valve that allows the hammer or thumb to share or sequence hydraulic flow where auxiliary circuits are limited.
Many compact excavators like the KH70 do not come from the factory with auxiliary hydraulics dedicated to a thumb. In such cases, owners either retrofit an auxiliary line using a diverter valve or tap into existing hydraulic circuits.
Reasons To Add A Hydraulic Thumb
Adding a hydraulic thumb significantly expands the machine’s utility:
• Material Handling — Logs, brush, rocks, demolition debris can be held securely.
• Site Cleanup — After excavation or clearing, a thumb allows one‑pass collection of irregular objects.
• Precision Placement — When setting fence posts, moving pavers, or placing utilities, a thumb gives controlled grip.
• Demolition Assistance — Breaking down small structures and then picking up pieces without manual labor.
Quantitatively, operators can often reduce cycle times by 20–40% for picking and placing irregular loads versus using the bucket alone.
Selecting A Thumb For An Older KH70
When choosing a hydraulic thumb, consider:
• Thumb Type — Top Mount thumbs attach near the boom and offer excellent reach and clearance. Side Mount thumbs attach to the stick and are simpler but may reduce reach slightly.
• Compatibility With Bucket Geometry — The bucket contour affects how the thumb and bucket mesh; a half‑moon or skeleton bucket often works best with thumbs.
• Hydraulic Requirements — Thumbs with their own cylinder need an auxiliary circuit or a diverter approach. Cylinder bore size (e.g., 1.5–2.0 in) and stroke determine grip force and range.
• Duty Cycle — For heavy brush or demolition, choose a heavy‑duty thumb with thicker plates and larger cylinders.
For the KH70, a thumb cylinder in the 40–60 cc/rev hydraulic flow range and pressures up to 2,500–3,000 psi is typical given the factory pump capacities and main control valve ratings.
Hydraulic Integration Options
Older KH70 models may lack a dedicated auxiliary hydraulic port. Options include:
• Diverter/Spool Valve Tap — This valve taps flow from an existing function such as swing or boom, redirecting it to the thumb when needed. It is cost‑effective but may require manual sequencing.
• Auxiliary Hydraulic Kit — Some retrofit kits add additional hydraulic lines, solenoid valves, and controls. These often use an inline flow diverter that senses pressure demand.
• Proportional Control — More advanced retrofits use proportional valves allowing fine thumb movement via a rocker or joystick button. While ideal, they are more complex to install.
• Hydraulic Quick Couplers — If the owner alternates between thumb and other attachments like hammers, quick couplers with integrated valves simplify the swap.
Installation Considerations and Best Practices
When installing a thumb on a KH70:
• Mounting Fabrication — Custom brackets must be welded or bolted to the stick or boom. Ensure high‑strength steel and proper reinforcements.
• Cylinder Alignment — Misaligned cylinders bind under load; use bushings and hardened pins sized for your machine’s duty.
• Hydraulic Hose Routing — Avoid sharp bends, high‑heat zones, and pinch points; use protective sleeves and clamps.
• Bleeding Air — Thoroughly purge air from new hydraulic circuits; trapped air leads to spongy operation.
• Control Logic — Decide whether thumb actuation will interrupt or share main function flow; set up diverters accordingly.
A common field tip is to route hoses inside the boom where possible, protecting them from snagging on brush or demolition material.
Troubleshooting Common Issues
Thumb installations may encounter:
• Weak Grip — Often caused by incorrect cylinder sizing or insufficient hydraulic flow. Increasing pump flow or using a larger cylinder helps.
• Jerky Movement — Air in lines or improper diverter sequencing; bleed lines and reconfigure valves.
• Bucket/Thumb Collision — Poor geometry; adjust thumb pivot or link length.
• Excessive Hose Wear — Reroute hoses with better protection at articulation points.
Field reports suggest that quick‑hoses designed with molded elbows and abrasion guards reduce maintenance costs by up to 30% compared with straight, unprotected hoses.
Case Story And Application Insight
A landscaper in Oregon retrofit a hydraulic thumb on an older KH70 to speed up removing uprooted trees and rocks after storms. Initially, he tried a mechanical thumb, but found it slow and fatiguing. After retrofitting a hydraulic thumb with a diverter valve, his cycle times for picking and loading debris dropped from an average of 15 minutes per pile to under 8 minutes — nearly doubling productivity. This mirrors broader industry experience: hydraulic thumbs save significant labor in irregular material handling.
Industry News And Trends
Today’s compact excavator designs increasingly include factory auxiliary hydraulic packages with proportional controls for thumbs and grapples, reflecting growing demand in landscaping, trenching, utility installation, and demolition. Major manufacturers like Kubota, Bobcat, and Caterpillar now prioritize electronics that allow smooth auxiliary function integration, a departure from older purely mechanical designs.
Parameter Guide For Thumb Performance
• Hydraulic Flow Needed for Thumb Cylinder — ~15–25 GPM
• Hydraulic Operating Pressure — ~2,000–3,000 psi
• Thumb Cylinder Bore — ~1.5–2.0 in
• Recommended Diverter Valve Size — ~20–30 cc/rev
• Typical Mount Pin Diameter — ~1 in or greater for durability
These figures ensure that the thumb functions reliably within the KH70’s hydraulic capacity.
Conclusion
Adding a hydraulic thumb to an older Kubota KH70 dramatically increases the machine’s versatility and productivity in material handling tasks. With careful selection of thumb type, appropriate hydraulic integration, correct mounting, and attention to control logic, owners can transform a basic excavator into a highly capable workhorse. Planning installation with proper geometry, hydraulic capacity, and protective routing are keys to a reliable retrofit that lasts through years of varied site work. A hydraulic thumb is one of the most cost‑effective performance upgrades for compact excavators tailored to real‑world landscaping, demolition, and forestry tasks.
Hydraulic Thumb Purpose And Terminology
A hydraulic thumb is an auxiliary attachment that works in concert with the excavator’s bucket to grasp objects. Terminology useful in this context includes:
• Hydraulic Thumb — A powered gripper mounted above or beside the bucket that actuates via its own cylinder.
• Auxiliary Hydraulic Circuit — A dedicated line from the excavator’s hydraulic pump and control valve that supplies fluid under pressure to additional attachments like thumbs or grapples.
• Thumb Cylinder — The cylinder on the thumb linkage that opens and closes the thumb.
• Mounting Bracket/Plate — The steel structure that connects the thumb assembly to the excavator’s arm or boom.
• Control Diverter/Flow Control Valve — A valve that allows the hammer or thumb to share or sequence hydraulic flow where auxiliary circuits are limited.
Many compact excavators like the KH70 do not come from the factory with auxiliary hydraulics dedicated to a thumb. In such cases, owners either retrofit an auxiliary line using a diverter valve or tap into existing hydraulic circuits.
Reasons To Add A Hydraulic Thumb
Adding a hydraulic thumb significantly expands the machine’s utility:
• Material Handling — Logs, brush, rocks, demolition debris can be held securely.
• Site Cleanup — After excavation or clearing, a thumb allows one‑pass collection of irregular objects.
• Precision Placement — When setting fence posts, moving pavers, or placing utilities, a thumb gives controlled grip.
• Demolition Assistance — Breaking down small structures and then picking up pieces without manual labor.
Quantitatively, operators can often reduce cycle times by 20–40% for picking and placing irregular loads versus using the bucket alone.
Selecting A Thumb For An Older KH70
When choosing a hydraulic thumb, consider:
• Thumb Type — Top Mount thumbs attach near the boom and offer excellent reach and clearance. Side Mount thumbs attach to the stick and are simpler but may reduce reach slightly.
• Compatibility With Bucket Geometry — The bucket contour affects how the thumb and bucket mesh; a half‑moon or skeleton bucket often works best with thumbs.
• Hydraulic Requirements — Thumbs with their own cylinder need an auxiliary circuit or a diverter approach. Cylinder bore size (e.g., 1.5–2.0 in) and stroke determine grip force and range.
• Duty Cycle — For heavy brush or demolition, choose a heavy‑duty thumb with thicker plates and larger cylinders.
For the KH70, a thumb cylinder in the 40–60 cc/rev hydraulic flow range and pressures up to 2,500–3,000 psi is typical given the factory pump capacities and main control valve ratings.
Hydraulic Integration Options
Older KH70 models may lack a dedicated auxiliary hydraulic port. Options include:
• Diverter/Spool Valve Tap — This valve taps flow from an existing function such as swing or boom, redirecting it to the thumb when needed. It is cost‑effective but may require manual sequencing.
• Auxiliary Hydraulic Kit — Some retrofit kits add additional hydraulic lines, solenoid valves, and controls. These often use an inline flow diverter that senses pressure demand.
• Proportional Control — More advanced retrofits use proportional valves allowing fine thumb movement via a rocker or joystick button. While ideal, they are more complex to install.
• Hydraulic Quick Couplers — If the owner alternates between thumb and other attachments like hammers, quick couplers with integrated valves simplify the swap.
Installation Considerations and Best Practices
When installing a thumb on a KH70:
• Mounting Fabrication — Custom brackets must be welded or bolted to the stick or boom. Ensure high‑strength steel and proper reinforcements.
• Cylinder Alignment — Misaligned cylinders bind under load; use bushings and hardened pins sized for your machine’s duty.
• Hydraulic Hose Routing — Avoid sharp bends, high‑heat zones, and pinch points; use protective sleeves and clamps.
• Bleeding Air — Thoroughly purge air from new hydraulic circuits; trapped air leads to spongy operation.
• Control Logic — Decide whether thumb actuation will interrupt or share main function flow; set up diverters accordingly.
A common field tip is to route hoses inside the boom where possible, protecting them from snagging on brush or demolition material.
Troubleshooting Common Issues
Thumb installations may encounter:
• Weak Grip — Often caused by incorrect cylinder sizing or insufficient hydraulic flow. Increasing pump flow or using a larger cylinder helps.
• Jerky Movement — Air in lines or improper diverter sequencing; bleed lines and reconfigure valves.
• Bucket/Thumb Collision — Poor geometry; adjust thumb pivot or link length.
• Excessive Hose Wear — Reroute hoses with better protection at articulation points.
Field reports suggest that quick‑hoses designed with molded elbows and abrasion guards reduce maintenance costs by up to 30% compared with straight, unprotected hoses.
Case Story And Application Insight
A landscaper in Oregon retrofit a hydraulic thumb on an older KH70 to speed up removing uprooted trees and rocks after storms. Initially, he tried a mechanical thumb, but found it slow and fatiguing. After retrofitting a hydraulic thumb with a diverter valve, his cycle times for picking and loading debris dropped from an average of 15 minutes per pile to under 8 minutes — nearly doubling productivity. This mirrors broader industry experience: hydraulic thumbs save significant labor in irregular material handling.
Industry News And Trends
Today’s compact excavator designs increasingly include factory auxiliary hydraulic packages with proportional controls for thumbs and grapples, reflecting growing demand in landscaping, trenching, utility installation, and demolition. Major manufacturers like Kubota, Bobcat, and Caterpillar now prioritize electronics that allow smooth auxiliary function integration, a departure from older purely mechanical designs.
Parameter Guide For Thumb Performance
• Hydraulic Flow Needed for Thumb Cylinder — ~15–25 GPM
• Hydraulic Operating Pressure — ~2,000–3,000 psi
• Thumb Cylinder Bore — ~1.5–2.0 in
• Recommended Diverter Valve Size — ~20–30 cc/rev
• Typical Mount Pin Diameter — ~1 in or greater for durability
These figures ensure that the thumb functions reliably within the KH70’s hydraulic capacity.
Conclusion
Adding a hydraulic thumb to an older Kubota KH70 dramatically increases the machine’s versatility and productivity in material handling tasks. With careful selection of thumb type, appropriate hydraulic integration, correct mounting, and attention to control logic, owners can transform a basic excavator into a highly capable workhorse. Planning installation with proper geometry, hydraulic capacity, and protective routing are keys to a reliable retrofit that lasts through years of varied site work. A hydraulic thumb is one of the most cost‑effective performance upgrades for compact excavators tailored to real‑world landscaping, demolition, and forestry tasks.
