WS39 casing tooth
JM cutter tooth
B47K22 bullet toothStart with the task that needs to improve: cutting the ground, lifting excavated material or recovering the core. Identify that task before comparing tools. A rock name or UCS value alone does not select the complete configuration.
Start with the problem at the site
Identify whether progress is limited by cutting, clearing or core recovery. Keep tool condition and the planned removal method with the ground information.
| Observed task or problem | Check first | Tool or system to review | Records to provide |
|---|---|---|---|
| A full-face tool makes poor progress in competent rock. | Ground interval, existing cutter condition and whether cuttings are leaving the cutting zone. | Discuss a core barrel and its core-breakout/recovery method, then compare roller-bit and bullet-tooth cutting arrangements. | Ground report where available, current tool photographs, rig details and separate cutting/clearing times. |
| Excavated material must be lifted and retained. | How material is held during lifting, with the actual bore-support and fluid conditions. | Compare an auger’s flights with a drilling bucket’s retention and discharge; base cleaning is a separate task. | Recovered material, hole/fluid context, present tool and the point where lifting or discharge fails. |
| The barrel advances, but core recovery delays the cycle. | Core dimensions and condition, the recovery sequence and the companion tool. | Review the recovery tool and sequence before attributing the delay to the cutting elements. | Cutting and recovery times, recovered-core views and the actual cutting envelopes of both tools. |
| Cuttings stay packed around the cutters or worn guides. | The connected route through the openings, scraper and guides; document it before cleaning. | Review the existing assembly and clearing method before expecting a different cutter family to remove the restriction. | Before-cleaning photographs, cutter condition, guide/scraper views and the intended layout. |
These are starting points for a configuration review, not fixed limits for a rock type. The comparison below explains each tool’s role; the ground-test references are retained after the trial-planning section.
Compare core barrels, augers and drilling buckets
A roller bit or bullet tooth is a cutting element. A core barrel, auger or drilling bucket is the assembly that supports cutters and manages excavation. Comparing all five as interchangeable alternatives obscures the decision. First choose the cutting and material-removal approach; then choose compatible cutters, mounting and wear protection.
| Tool | When to discuss it | What to confirm |
|---|---|---|
| Core barrel | Forms an annular cut around a core; discuss it when full-face excavation makes poor progress in competent rock. | Core breakout and recovery, inner and outer cutting paths, cuttings removal and rig capacity. Then compare bullet-tooth and roller-bit cutting rings. |
| Rock auger | Chips ground and carries cuttings on its flights. | Fragment size and retention, a suitable tooth arrangement, available torque and crowd, and the bore support method. |
| Drilling bucket | Cuts, retains and lifts material; useful where excavated material must be retained through a liquid-filled hole. | A suitable cutting bottom, filling and discharge. Base cleaning needs a suitable clean-out tool. |
BAUER’s official range illustrates why augers, buckets and core barrels serve different roles; its tool-family descriptions are useful context, not ratings for a DRILLNOVA model. BAUER drilling-tool overview
For a core barrel, the narrower annular cut concentrates the applied load around the perimeter. Cutting the ring does not automatically release or lift the core: recovery must be planned alongside penetration. A drilling bucket and a purpose-designed clean-out bucket also have different jobs. FHWA, sections 4.3.1.2–4.3.1.3
Cutting, core recovery and hole cleaning may require different tools in the same pile. In the Guangdong field record, the crew used a core barrel and bucket in sequence, then changed to direct bucket work after clearing and reviewing the recovered ground. Read the Guangdong change-of-method case.
Short soil augers: material entry and emptying both matter
A short auger needs to receive excavated material between its flights, carry the load and release it after lifting. The cutting teeth are only one part of that cycle.
In the AGS soil-auger design discussed in Liu Sanyi’s 2008 study, changing the flight geometry involves a trade-off. At a fixed auger diameter, the study describes these two limits:
| Flight geometry | What the study explains |
|---|---|
| Small pitch, with closely spaced flights | Soil can become crowded between the flights, making emptying difficult. |
| An excessively steep helix | Resistance to soil entering the flights can increase. |
A larger gap is therefore not an automatic improvement. Diameter, flight slope, pitch and the soil’s interaction with the steel need to be considered together. A load packed between flights is a different observation from poor material entry; neither observation alone establishes the cause.
This explanation concerns the study’s short soil augers. It does not specify a pitch, rotation speed or unloading procedure for another tool, and it is not a design rule for rock augers or continuous-flight auger piling.
Technical reading: Liu Sanyi, Multi-process Rotary Drilling Technology Research, doctoral thesis, 2008, Chapter 4, sections 4.2.1 and 4.2.3.1. This is a third-party design explanation, not a DRILLNOVA field-performance result.
A bucket bottom: distinguish inlets, layers and discharge
“Double bottom” does not by itself mean “two inlets”. The layer count describes the bottom assembly; the inlet count describes where excavated material enters. Emptying the bucket is a third question: identify how the complete bottom opens, rather than treating an inlet closure as the discharge mechanism.
In the BSS/BSR examples described in Liu Sanyi’s 2008 study, a single-layer bottom uses internal flaps at the inlets. The described two-layer version closes its inlets by offsetting the openings between layers and does not use those flaps. Confirm which arrangement the actual drawing specifies; do not add an assumed flap to a two-layer design.
| Question | Useful evidence | What it cannot establish alone |
|---|---|---|
| How many material-entry openings? | A labelled bottom plan or clear underside photograph, with inlet boundaries identified. | Internal layer count. Do not count ventilation or other holes as soil inlets without tracing their function. |
| What keeps material inside? | A section or assembly drawing showing the layers and the specified flap or offset closure. | A general side photograph does not confirm concealed flaps or the closure arrangement. |
| How does the bucket empty? | An assembly view identifying the bottom hinge and release mechanism. | Inlet count or clear passage size. An inlet closing and the complete bottom opening are different movements. |
For coarse fragments, compare the clear passage as well as the number of openings. The study’s BSG example uses one opening to increase the available passage in that design. This does not make every single-inlet bucket suitable for larger fragments. Ask for the actual opening shape, measurement endpoints and clear dimensions on the selected drawing.
Technical reading: Liu Sanyi, Multi-process Rotary Drilling Technology Research, doctoral thesis, 2008, Chapter 3. The distinctions above explain selected third-party designs, not a DRILLNOVA model or field-performance result. Use the actual manufacturer’s drawing and operating procedure for the equipment.
When to compare roller bits with bullet teeth
Compare roller-bit and bullet-tooth core-barrel configurations with the ground interval, rig capability, mounting and recovery method. First identify whether the existing limitation is cutting, wear, blocked cuttings or recovery; a larger insert or another cutter family does not address all four.
BAUER documents round-shank-chisel and roller-bit barrels with different application ranges and describes its selection chart as non-binding. Use that information to frame a comparison, not to turn a rock name into a DRILLNOVA model recommendation. BAUER core-barrel catalogue
A strong piece is not the whole rock mass
Joints, bedding, weathering and infill influence how the excavation separates. Record discontinuity spacing and orientation alongside core recovery and RQD; none replaces an intact-rock test. Water inflow can also vary between nearby boreholes. Read these observations together rather than treating one laboratory result as a complete description. FHWA, Chapter 2
In rotary bored piling, hard cobbles do not necessarily require the same cutting approach as intact bedrock. In a weakly cemented or uncemented cobble–gravel deposit, the task may be to loosen and collect existing particles rather than break each one into smaller pieces. Liu Sanyi’s study describes bullet teeth stirring these particles loose so that they can enter the drilling bucket. The hardness of one recovered cobble therefore does not describe the task for the whole layer. Check whether the particles are loosely bound or cemented together before comparing cutting systems; this explanation does not establish the method for a cemented deposit.
Technical reading: Liu Sanyi, Multi-process Rotary Drilling Technology Research, doctoral thesis, 2008, section 7.3.1, pp. 105–106. This is a third-party explanation of low-cementation ground, not a DRILLNOVA field result or an operating-parameter recommendation.
Measure the next trial across the complete cycle
Keep depth interval, assembly, cutter positions and operating observations together. Record penetration time separately from core breaking, lifting, emptying and cleaning, then compare wear after a defined interval. This practical comparison is more useful than a blanket promise for “granite.” Send the ground report and current assembly through a cutting-system review; use our core-barrel selection guide for the configuration details.
Intact-rock UCS: published test examples
These named specimens show measured uniaxial compressive strength (UCS), not fixed ranges for each rock type.
| Rock | Specimen | UCS (MPa) |
|---|---|---|
| Granite | Nevada Granite Pikes Peak Granite | 141.1 226.0 |
| Basalt | Nevada Basalt John Day Basalt | 148.0 355.0 |
| Limestone | Bedford Limestone Solenhofen Limestone | 51.0 245.0 |
| Sandstone | Berea Sandstone Navajo Sandstone | 73.8 214.0 |
| Shale | Flaming Gorge Shale Micaceous Shale | 35.2 75.2 |
| Marble | Taconic Marble Cherokee Marble | 62.0 66.9 |
| Gneiss | Dworshak Dam Gneiss | 162.0 |
| Quartzite | Baraboo Quartzite | 320.0 |
Source: FHWA NHI-01-031, Table 10-4 (2001; after Goodman, 1989).
Cementation, porosity, weathering and loading direction affect strength. Use your project’s test results for selection.
Read the strength classes
- R0 · Extremely weak0.25–1 MPa
- R1 · Very weak1–5 MPa
- R2 · Weak5–25 MPa
- R3 · Medium strong25–50 MPa
- R4 · Strong50–100 MPa
- R5 · Very strong100–250 MPa
- R6 · Extremely strong>250 MPa
FHWA NHI-11-032, Table 4-7 (2011).
Mohs, UCS and abrasivity answer different questions
Two intervals logged as granite can need different drilling approaches. One may be weathered and closely jointed; another may be massive and abrasive. A useful tool decision separates mineral hardness, intact-rock strength, wear potential and rock-mass structure before comparing cutters.
Mohs hardness ranks resistance to scratching. It describes minerals: USGS lists calcite at 3 and quartz at 7. It is not a compressive-strength scale, and a rock containing quartz does not acquire one universal drilling rating. A scratch observation can help identify a mineral; it cannot be converted into a reliable UCS value. USGS mineral-hardness reference
Uniaxial compressive strength (UCS) describes failure of a prepared intact specimen under axial compression without lateral confinement, commonly reported in MPa. The test result belongs to that specimen and its condition. Preserve depth, test method, moisture condition and sample orientation when forwarding results. A point-load index is a different test result; do not silently relabel it UCS. BGS explanation of strength tests
Abrasivity concerns the rock’s tendency to wear a cutting tool. The CERCHAR Abrasiveness Index measures wear of a specified steel stylus scratched across a freshly broken rock surface, or a saw-cut surface where the test method permits. Surface preparation and stylus hardness affect the result. This is why “high strength” and “high wear” should be separate fields in a selection discussion. CAI is an index for comparison, not a direct prediction of the metres a particular roller bit will drill. ASTM D7625 public scope