Auger for Mini Excavator: Sizes and Drilling Guide
Qisheng Machinery · Updated October 16, 2026
Quick Answer
Choosing an auger for mini excavator drilling starts with the required hole diameter, finished depth and ground conditions. Then select a bit, drive and carrier combination that the relevant manufacturers approve for that work. “Fits a mini excavator” is not enough information to select the assembly.
Separate the parts in the enquiry: the hydraulic drive turns the bit, the mounting arrangement connects the drive to the excavator, and any extension changes the drilling assembly. Each needs its own identification and limits. A larger bit or a longer extension is not automatically a usable upgrade.
Describe the Hole Before Choosing the Bit
| Job information | What to state | Why it changes the selection |
|---|---|---|
| Hole diameter | Required finished diameter and any applicable project specification | Establishes the bit size to review |
| Hole depth | Finished depth from the stated ground level | Determines whether the proposed assembly can reach and clear the hole |
| Ground | Soil description, known rock, fill, roots or other obstructions | Affects cutting tools and the maker's diameter recommendation |
| Quantity and layout | Number of holes, spacing, access and available setup area | Helps plan the machine position and repeat work |
| Carrier | Exact model/version and available auxiliary circuit data | Determines whether the selected drive can be supplied and controlled |
For fence posts or structural work, use the hole dimensions required by the project designer or applicable installation specification. A drill-size guide is not a foundation design. Do not choose an oversized hole merely because the supplier offers a large bit.
As an enquiry example, “twenty holes, 300 mm finished diameter, 900 mm deep, clay with occasional stones” gives the supplier a useful starting point. It does not establish which drive will work or promise a drilling rate. The ground still needs assessment and the actual machine-tool combination needs confirmation.
See How Ground Conditions Change Published Diameter Limits
Digga's published micro-excavator drive table provides a named example of the information needed:
| Digga drive | Recommended flow range | Maximum recommended auger diameter: clay/shale | Maximum recommended auger diameter: earth |
|---|---|---|---|
| PDD | 15–45 L/min | 400 mm | 500 mm |
| PDX | 20–50 L/min | 400 mm | 600 mm |
| PDX2 | 30–50 L/min | 450 mm | 600 mm |
Source: Digga micro-excavator auger drives, checked October 16, 2026. Digga identifies its diameter figures as recommendations dependent on ground conditions. These specifications belong to those Digga models. They are not ratings for Qisheng's listed auger option, and the table does not confirm that any QS machine is compatible.
The example makes two practical distinctions. The same drive can have different recommended diameters in different ground. Different drives also have different recommended flow ranges; the largest diameter in a product range is not a rating for every model in it.
Match the Drive and Plan the Drilling Depth
Obtain the chosen drive's operating-flow and pressure requirements, return or drain requirements, mounting details, output-shaft interface and approved bits. Compare them with the auxiliary circuit of the exact excavator. Matching only the nominal machine class can miss an unsuitable circuit or control arrangement.
The Qisheng catalogue illustrates an optional auger but does not establish its drive model, operating flow, torque, permitted bit sizes or depth limits. Request those specifications for the quoted assembly. Do not infer them from QS engine power or use the Digga figures as substitute QS data.
For depth, review the usable bit length, the maker's extension arrangement and whether the carrier can insert, withdraw and clear the complete assembly. Catalogue maximum excavator digging depth is measured for its digging arrangement; it does not automatically become auger drilling depth.
An extension also changes the handling and clearance of the assembly. Ask how it is attached, retained, inserted and removed under the applicable instructions. Do not create a depth claim by adding an extension length to the excavator's bucket-depth figure.
Plan the First Holes and the Wear Parts
Before drilling, have buried services located and assess the ground and working area. Use the carrier and tool manuals for setup, exclusion space and operating procedures. A nearby helper should not approach a rotating assembly to guide or clear it.
For the first holes, check the location, diameter and achieved depth against the job requirements. If the bit stalls, encounters an unexpected obstruction or produces unsuitable results, stop and reassess the ground, cutting parts and approved settings rather than assuming more force will solve the problem.
Ask for the part references and replacement procedure for teeth and pilots, and for the drive's own maintenance information. Soil, clay and rock cutting arrangements should be selected using the tool maker's recommendations. A general “rock auger” label does not establish suitability for every rock formation.
For circuit and installation questions, use the separate attachment compatibility checklist. This page focuses on the hole specification, bit size and depth plan.
Frequently Asked Questions
What size auger should I use for fence posts?
Start with the required finished hole from the post installation specification, then ask for a bit and drive suitable for that diameter and the actual ground. There is no universal diameter for every post, soil and foundation requirement.
Can a QS-18 use a 600 mm auger because another manufacturer's table lists one?
That conclusion cannot be drawn. The cited 600 mm entries belong to particular Digga drives under stated ground recommendations. The QS carrier and quoted tool require their own confirmed ratings and compatibility review.
Is excavator digging depth the same as auger drilling depth?
No. Auger depth depends on the specified bit/extension assembly, its handling limits and the carrier's usable geometry. A bucket-depth entry alone does not answer the question.
Request the Right Assembly
Use the attachment compatibility checklist to gather the technical information. Compare the QS-12 and QS-18 carrier options with the actual tool requirements.
Ask Qisheng about an excavator-and-auger configuration. Include the hole diameter, depth, number of holes, ground description and destination. Request the drive identity, bit dimensions and confirmed circuit match in the quotation.