Hydraulic Auger Selection: Rock vs. Earth - Which One Do You Need?

20 November 2025

Hydraulic earth augers are used in a wide range of applications, from landscaping to solar power plant (PV) installations, utility pole erection, and fencing. However, the biggest mistake made on site is choosing an auger or tooth type that is unsuitable for the ground conditions.

At HKM, we explain how to choose the right drive unit and teeth type so you don't have to stop in the middle of your project.

1. Critical Decision: Teeth Type

No matter how powerful the auger drive unit is, it is the teeth that cut the ground. Choosing the wrong teeth can burn out the auger motor.

Earth Teeth: Designed for soft soil, clay, and sandy ground. Usually flat with a wide cutting edge. They lift the soil out quickly.
Tungsten (Rock) Teeth: Hard, rocky, asphalt, or frozen grounds require diamond-tipped (tungsten carbide) teeth. These teeth do not scoop; they grind and fracture the ground.

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2. Torque vs. Speed Balance

Your excavator's hydraulic flow determines the speed (RPM), while pressure determines the torque (rotational force).

Hard Ground (Rock): Requires High Torque / Low Speed. Power is needed to fracture the rock.
Soft Ground (Soil): Requires Low Torque / High Speed. Spinning the soil off quickly is key.

3. Teeth Selection Table

Which tooth type should you choose for your ground?

Ground Type	Recommended Teeth	Operation Tip
Agricultural Soil / Sand	Standard Earth Teeth	Operate at high RPM.
Clay / Compacted Soil	Taper Teeth	Use a sharp pilot bit.
Gravel / Asphalt	Tungsten Carbide Teeth	Low speed, high down pressure.
Rock / Concrete	Rock Series	Must use heavy-duty auger body.

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Frequently Asked Questions (FAQ)

Q: My auger is spinning but not drilling, why?
A: Usually two reasons: 1) Your teeth might be dull. 2) The pilot bit (the center point) is not penetrating the ground. If the pilot is worn, the auger cannot stabilize and will just spin on the surface.

Q: Do I need an extra line from my excavator?
A: In most cases, the hydraulic breaker line (hammer line) is used for the auger. However, if you need the auger to rotate in both directions (reverse), ensure your machine has a bi-directional hydraulic line.