Volvo construction uses an innovative pin-on thumb design that allows the thumb to be used on its extendible dipper with an inner slide design.
An extendible dipper stick can add 5% or more to the cost of a backhoe-loader and typically extends the reach 3 to 4 ft. Productivity gains through the extra reach often pay for this option very quickly. However, there are two very distinct ways to achieve the desired result. One design extends the inner portion of the dippe,r while the other design extends to outer portion of the dipper. There are pros and cons on both sides of it.
The JCB backhoe-loader configures the extendible dipper by allowing the inner section to travel out and away from the tractor. “The lighter part goes away from the tractor giving more capacity in lifting a bucket or suspended load at reach,” says Jim Blower. “This design can be adjusted be re-torquing eight bolts. The whole design can be cleaned out of any dirt or water very easily as it is open.” A disadvantage is the thumb becomes a little more complicated to install.
The design allows the hoses and auxiliary hydraulics to be run inside the boom and dipper. “This means they are protected and not hanging on the outside of structures in a vulnerable place,” says Blower.
Volvo also uses an extendible inner dipper stick design. “We extend the inner part of the dipper as opposed to some of our competitor’s extending the outer part, which is the heaviest part,” says Marcello Bargellini, backhoe product specialist. “By extending the lighter part, we actually gain lift capacity. It is much easier to adjust, as well.”
The pads may only have to be adjusted every 500 or 600 hours, and are very easy to replace. External screws areremoveed to take the old pad out and put a new oil-impregnated pad in. “In about 20 minutes, you are done," says Bargellini.
Volvo developed a unique way to connect a thumb to the inner dipper design. “We do install a thumb on this machine, which is a factory-installed thumb,” says Bargellini. “We can retrofit it, as well. The thumb doesn’t require any welding.” All you have to do is remove the shorter pin and install the longer pin that comes in the kit. There is a tip extension that can be bolted on if you are using a coupler. This allows the thumb to line up with the teeth on the bucket.
While some manufacturers believe the benefits of the inner slide outweigh the negatives, there are others who believe an outer slide is the better option. An advantage of having the outer part of the dipper extend is it limits exposure of the slide mechanism to the trench. In addition, the serrated edge on an outer box design allows for easy clamping
Case backhoe-loaders use an outer slide design. “The main advantage of the outer-type extendible dipper is that it prevents ingress of dirt and debris into the dipper assembly when the extendible section is retracting inward,” says George MacIntyre, global product marketing manager. This design also allows a more straightforward installation and use of a thumb attachment on the dipper. “Similar to installation of a thumb, auxiliary hoses are routed and secured better on an outer type extendible dipper because of the fixed mounting points on the outer section.”
Terex uses a similar approach. “The outer extender on the TLB840’s dipper stick keeps the slide area clean from debris that can damage inner expender slide components, making plumbing and use of a thumb attachment more effective and useful,” says Jamie Wright, product manager. “The TLB 840 is designed with a greaseless outer extendible dipper, which allows the components of the extender to remain protected from dirt and prevents water from entering into the wear portion of the stick.
“The thumb and the auxiliary hydraulic connectors can travel with the outer extender, allowing the unit to pick and place rocks and other objects further away from the unit," he continues. "The replaceable serrated section at the end of the dipper is valuable when clamping objects to the stick.”
According to Wright, “Inner dippers do not allow the plumbing to move with the extendable portion of the dipper, where the outer extendible dippers carry the auxiliary hydraulics to travel with the extendible dipper. This allows attachments like thumbs to be used at full extension.”
Caterpillar's Kevin Hershberger touts two specific advantages of the Cat outer slide design: it eases serviceability and it allows installation of the Caterpillar hydraulic thumb. “With this design, the wear pad system can be adjusted in the field, using common hand tools, and the hydraulic thumb can be used through the full extension range of the E-Stick," he says.