Almost every excavator manufacturer offers long boom and stick configurations, ranging from a few feet of added reach to in excess of 60 ft. "Super Long Front excavators stretch the digging reach of regular excavators by as much as double," notes Matthew Hendry, product consultant - hydraulic excavators and ADTs, Deere & Company.
Aftermarket attachments are also available in a range of lengths. For example, Paul Wever Construction Equipment engineers sticks and booms from 8 up to 100 ft. of additional reach. "I am a custom builder, so people come to me with their specific needs and we build the extensions that meet the specific job," says Paul Wever.
Such attachments provide more flexibility than OEM long-reach setups, which tend to be dedicated machines. "Obviously, you cannot start lifting manhole covers with a machine that has 60 ft. of reach. So it is hard for some end users to justify having that single tool if they don?t have work for it all of the time," says Wever. "With our attachment, they can add it to the excavator, do their job, then take it off and go back to normal trench digging." The switch takes about three to four hours with a typical 40,000- to 70,000-lb. excavator.
Whether you choose a dedicated machine or aftermarket attachment, there are trade-offs associated with the additional reach. "Lift capacity will be reduced and dynamic instability increased, resulting in the perception of tippiness," says Lew Miller, director of engineering, LBX Co., supplier of Link-Belt excavators.
In addition, long sticks and booms are more easily damaged if not used properly. "Longer booms and sticks are more susceptible to twisting forces than standard-length attachments," says Bret Jacobson, product manager, earthmoving excavators, Liebherr Construction Equipment Co. "Side loads induced through the bucket into the stick and boom will fatigue these structures over time... In some cases, for very long attachments, the stick cylinders and bucket cylinders are downsized to keep forces on the attachment within a range that the boom and stick can safely withstand."
More length equals less force
Digging forces on dedicated long front (LF) machines have been adjusted by the OEMs to optimize their capabilities without sacrificing equipment longevity. "Digging forces are lowered on LF machines in order to ensure that the front structures provide acceptable life for the customer," Hendry explains. "This is accomplished by lowering the hydraulic relief pressures."
These settings should not be adjusted in the field, since this is likely to result in structural problems. "Our engineers have done the math and know what the machines can safely handle with a LF boom/arm," says Hendry. "Contractors should not change the machine?s settings or they risk very expensive repairs or replacement of the boom/arm."
With aftermarket attachments, there is a risk if the hydraulic relief settings on the host machine are not matched to the increased leverage of a longer stick and boom.
"Failing to lower the digging forces will cause rapid damage to pins and bushings at the boom/arm connection and possibly cause other structural damage," Hendry explains. "There are tremendous leverage forces being applied when you add several feet of length to a standard excavator boom/arm. So extreme caution must be used or the low-cost option of the [boom/arm extension] could become a very expensive option because of damage to the host machine."
Care must also be taken to calculate available crowd force. "Since the crowd force is proportional to the length of the stick, a contractor can estimate a percentage decrease in crowd force compared to how much longer the stick is from standard," says Jacobson. "If there is any doubt, the contractor should request a calculation from the attachment manufacturer to be sure that the long attachment will suit the application at hand."