Many times, skid steer-mounted auger attachments don’t perform as expected, and the attachment is blamed. In reality, the problem may be a mismatch between the carrier and the auger, or they are simply not set up properly for the task.
“It’s about balance involving machine weight, power, system pressure/flow rates, auger diameter, digging depth and soil classification,” says Dennis Von Ruden, president, General Equipment Co. “For something as primitive as digging a hole, it’s not always simple.”
First, size the auger to the flow and pressure the carrier can produce. “Because drive strength depends on the hydraulic flow and pressure produced by the skid steer, choosing an auger that is too big will put unnecessary stress on the skid steer and keep it from running efficiently,” says Dave Aldrich, light construction dealer development and service manager for Paladin Construction Group, which includes McMillen auger attachments.
Auger diameter is directly influenced by the size of the auger drive. “Make sure to pick an auger drive to match the flow and pressure of the skid steer (standard or high flow) and that will handle the diameter of the auger that you would like to use,” says Danuser’s Glenn Danuser.
Ron Peters, product manager, CEAttachments, notes that most skid steers offer very comparable pressure ratings; the critical differences are in the flow ratings. “When you choose an auger, you need to know some specs on your machine,” he states. “If your skid steer puts out 20 gpm, you want to make sure you size your auger correctly.” If you know the skid-steer make and model, it’s easy to look up the specs.
The skid steer hydraulic system dictates the auger drive size and bit size needed to run efficiently. “When customers come through the door, we ask what kind of hydraulic system their skid steer is running and then recommend the best auger based on this information and their digging conditions,” says Aldrich.
Torque vs. speed
The digging torque produced by an earth auger attachment is a direct function of the hydraulic system pressure relief setting.
“Torque is not directly dependent upon the attachment itself,” says Von Ruden. “The hydraulic pump of the skid loader produces pressure, which ultimately produces the digging torque. Auger rpm is a direct function of hydraulic system flow rate. Generally speaking, the higher the flow rate, the faster the auger will rotate.”
Von Ruden adds, “Operators will blame the earth auger attachment for not having sufficient torque or rotation speed when the problem really lies with the skid loader or backhoe not being properly matched. Any earth auger attachment will only function with what it is given to work with in terms of pressures and flow rates.”
Generally, smaller augers run at a higher speed. “As you drive to higher torque, the speed usually drops,” notes Peters. You don’t want a 36- or 48-in.-diameter auger spinning as fast as a 12-in.-diameter auger. “You need more torque because you are covering a larger area.”
He adds, “For our smaller drive units, at 20 gpm, they are turning 93 rpm. If you go to a larger one at 30 gpm, it is turning 66 rpm.” Then there are high-flow units. “That is going to have a lot more torque. It can handle more flow. The speed on that unit can change drastically depending upon the flow that you are putting into it.”
To effectively choose between torque and speed, you must understand the digging conditions. “When working with good digging conditions such as sand, clay and loam soils, choose an auger for its speed to increase productivity,” says Aldrich. “Choose an auger with a higher volume of torque to break up harder materials such as compacted soil, asphalt, concrete and frozen surfaces.”
The tougher the conditions, the larger the hole, and the deeper the hole, the more you will prefer torque over speed. “Nine out of 10 people we speak with choose torque over speed,” says Danuser. “Speed would be the best choice if you are digging in plain dirt or sand to allow the auger to throw the material off the auger.”