A contractor in Indonesia switched from flat teeth to bullet teeth on a weathered sandstone project. His drilling time dropped by 30 percent and his tooth replacement frequency fell from every 40 meters to every 120 meters. But on a separate clay project nearby, the same crew switched back to flat teeth, because bullet teeth were overkill and cost twice as much per unit.
The right tooth depends on the ground, not the brand.
Choosing between bullet teeth and flat teeth is one of the most common decisions contractors face on foundation drilling projects. Get it right, and you save thousands of dollars per pile. Get it wrong, and you burn through replacements, waste rig hours, and blow your budget.
This guide provides a data-driven comparison of bullet teeth vs flat teeth. You will learn exactly when to use each type, how to calculate cost-per-meter for your specific ground conditions, and how to use hybrid configurations when your project involves mixed geology.
For a complete overview of bullet tooth specifications, models, and applications, see our complete bullet teeth selection guide.
Introduction of Bullet Teeth
Bullet teeth, also called conical teeth, are carbide-tipped cutting tools designed for drilling through hard ground. They have three main components: a tungsten carbide tip, an alloy steel body (typically 42CrMo), and a retaining system that locks the tooth into a holder.
The defining feature of bullet teeth is their conical geometry. The pointed carbide tip concentrates force onto a small contact area, which allows the tooth to fracture rock and dense material efficiently. Most bullet teeth are designed to self-rotate in their holders during drilling. This rotation distributes wear evenly around the carbide cone, creating a self-sharpening effect that extends service life significantly.
The carbide tip itself rates between HRC 88 and HRC 92 on the hardness scale, while the steel body sits at HRC 40 to 45 after heat treatment. This combination gives bullet teeth the hardness to cut rock and the toughness to absorb impact without shattering.
Bullet teeth are the standard choice for weathered rock, hard rock, gravel, cobbles, and mixed formations above 15 MPa. Common models include the B47K series (B47K19, B47K22, B47K22H) and the C31HD. If you want to understand the applications of Bullet Teeth, please check out our article about How Bullet Teeth Are Used.
Introduction of Flat Teeth
Flat teeth, also called chisel teeth, are cutting tools with a flat or scoop-shaped edge designed for soft ground excavation. Unlike bullet teeth, flat teeth use a wider cutting profile that shears material rather than fracturing it.
Most flat teeth are made from alloy steel with optional hardfacing or carbide overlay on the cutting edge. The steel body is typically heat-treated to HRC 38 to 45. Some premium flat teeth include a thin carbide strip welded to the edge for improved wear resistance, but they do not have the large, replaceable carbide insert found on bullet teeth.
Flat teeth mount directly to the auger flight or bucket lip, usually through weld-on or bolt-on holders. They do not self-rotate. Instead, they maintain a fixed cutting angle throughout the drilling cycle.
The wider cutting edge makes flat teeth highly efficient in soft materials. They move more volume per rotation than bullet teeth in clay, sand, silt, and loose fill. They also produce smoother borehole walls, which matters for projects where hole quality affects pile integrity.
Flat teeth are the standard choice for ground below 20 MPa, including topsoil, soft clay, sand, and uncompacted fill. They cost less per unit than bullet teeth and are simpler to replace in the field.
Bullet Teeth vs Flat Teeth: Side-by-Side Comparison
The table below covers the technical differences that matter on the job site.
| Feature | Bullet Teeth | Flat Teeth |
|---|---|---|
| Shape | Conical / pointed | Flat / chisel |
| Material | Tungsten carbide tip + alloy steel body | Steel body (carbide overlay optional) |
| Carbide hardness | HRC 88–92 | HRC 55–65 (if overlay present) |
| Body hardness | HRC 40–45 | HRC 38–45 |
| Self-rotation | Yes (most designs) | No |
| Self-sharpening | Yes (via rotation) | No |
| Best ground conditions | Rock, gravel, dense soil, mixed | Clay, sand, silt, soft soil |
| Effective MPa range | 15–100+ MPa | Below 30 MPa |
| Penetration rate in rock | High | Low to moderate |
| Penetration rate in soft soil | Moderate | High |
| Borehole wall quality | Moderate (may be rougher in soft ground) | Good (smooth walls) |
| Unit cost | $8–25 per tooth | $3–10 per tooth |
| Service life in medium rock (40 MPa) | 80–150 meters | 20–40 meters |
| Service life in soft clay | 200–400 meters | 300–500 meters |
| Replacement difficulty | Moderate (holder system) | Easy (weld-on or bolt-on) |
| Energy consumption in rock | Lower | Higher |
| Energy consumption in soft soil | Higher | Lower |
The fundamental difference comes down to the cutting mechanism. Bullet teeth use a point-attack approach: the conical tip applies extreme pressure to a tiny area, cracking and fracturing the material. Flat teeth use a shearing approach: the wide edge slices through soft material like a blade. Point-attack is more effective in hard, brittle ground. Shearing is more effective in soft, cohesive ground.
When to Choose Bullet Teeth
Choose bullet teeth when your project involves any of the following conditions:
Ground conditions:
- Weathered rock above 15 MPa
- Hard rock above 60 MPa
- Gravel and cobbles
- Mixed formations with rock layers
- Dense or cemented soil
Tool types:
- Rock augers
- Rock drilling buckets
- Core barrels
- Casing shoes for rock penetration
Project characteristics:
- Deep foundations reaching bedrock
- Bridge piers and high-rise piles
- Projects with variable geology (soft overburden over rock)
Decision checklist:
- Ground investigation shows MPa values above 30
- Flat teeth are wearing out in under 50 meters
- Drilling speed has dropped below acceptable rates
- The rig is operating at high torque for extended periods
- Borehole depth requires penetration through rock layers
When to Choose Flat Teeth
Choose flat teeth when your project involves any of the following conditions:
Ground conditions:
- Clay below 10 MPa
- Sand and silt
- Soft fill and topsoil
- Unconsolidated alluvium
- Peat and organic soils
Tool types:
- Soil augers
- Cleaning buckets
- Soft-ground drilling buckets
- CFA (continuous flight auger) tools
Project characteristics:
- Shallow piles in soft ground
- CFA piling in clay or sand
- Utility augering
- Projects where borehole wall smoothness matters
Decision checklist:
- Ground investigation shows MPa values below 20
- High penetration speed in soft material is the priority
- Borehole wall quality affects pile skin friction
- Budget constraints favor lower-cost tooling
- The project does not require rock penetration
For more on soil drilling applications, see our soil auger drilling guide.
Hybrid Configurations: Using Both Together
Many projects involve mixed geology: soft clay over bedrock, or fill over gravel. In these cases, using both bullet and flat teeth on the same tool, or switching between tools during the bore, often delivers the best results.
Common hybrid configurations:
- Outer ring bullet teeth + center flat teeth on a drilling bucket. The bullet teeth on the outer ring cut the harder perimeter material, while the flat teeth in the center excavate the softer core. This works well in mixed ground where the outer formation is harder than the inner material.
- Pilot bullet tooth + flat flight teeth on an auger. The bullet pilot tooth breaks through hard spots or rock lenses, while the flat teeth on the flights carry the bulk of the soft material removal.
- Sequential use by depth. Start with flat teeth for the soft overburden (top 5 to 15 meters), then switch to bullet teeth when the auger reaches the rock interface. This avoids wasting expensive bullet teeth on material that flat teeth handle faster and cheaper.
A contractor in Malaysia used this sequential approach on a project with 12 meters of clay over granite bedrock. By drilling the clay with flat teeth and switching to bullet teeth only for the granite, the crew saved over $2,000 per pile compared to using bullet teeth from the surface.
Hybrid configurations make sense when the cost savings from using flat teeth in soft layers outweigh the time required to change tools. For custom tooth arrangements on your drilling equipment, see our custom drilling configurations page.
Cost-Per-Meter Analysis
Upfront cost tells you nothing. What matters is cost per meter drilled, which accounts for tooth price, service life, and drilling speed.
Upfront cost comparison:
| Tooth Type | Unit Cost Range | Typical Set (per bucket) |
|---|---|---|
| Bullet teeth (B47K22) | $12–22 per tooth | $96–176 (8 teeth) |
| Flat teeth (standard) | $4–8 per tooth | $32–64 (8 teeth) |
Cost-per-meter by formation:
| Formation | MPa Range | Bullet Teeth | Flat Teeth |
|---|---|---|---|
| Soft clay | Below 10 | $0.08–0.12/m | $0.04–0.08/m |
| Sand / silt | 5–15 | $0.10–0.15/m | $0.06–0.10/m |
| Gravel | 15–30 | $0.15–0.25/m | $0.30–0.50/m |
| Weathered rock | 30–60 | $0.15–0.25/m | $0.40–0.80/m |
| Hard rock | 60–100+ | $0.25–0.40/m | $0.80–1.50/m |
The break-even point is around 30 MPa. Below 30 MPa, flat teeth cost less per meter because they are cheaper per unit and last longer in soft ground. Above 30 MPa, bullet teeth cost less per meter because their longer service life in rock offsets the higher unit price.
Consider the full picture. A set of bullet teeth at 150 that lasts 120 meters in weathered rock costs 1.25 per meter for tooling alone. A set of flat teeth at 50 that lasts 30 meters in the same rock costs 1.67 per meter. Add the downtime for three extra tooth changes, and the flat teeth option becomes even more expensive.
Drilling Parameters by Tooth Type
Tooth type affects how you configure your rig. The differences are not dramatic, but they matter for optimizing performance and avoiding premature wear.
RPM recommendations:
- Bullet teeth: 15 to 30 RPM in rock; higher RPM in soft ground risks unnecessary carbide wear
- Flat teeth: 25 to 45 RPM in soft ground; lower RPM in harder formations to reduce tooth stress
Crowd pressure:
- Bullet teeth require higher crowd force to achieve effective point loading on rock
- Flat teeth work with lower crowd pressure in soft ground; excessive force causes the teeth to dig in and stall the rotation
Torque requirements:
- Rock drilling with bullet teeth typically demands 60 to 100 percent of the rig’s rated torque
- Soft ground drilling with flat teeth usually requires 30 to 60 percent of rated torque
These parameters also influence kelly bar selection. Projects that use bullet teeth in hard rock benefit from friction-type kelly bars that absorb torque spikes, while interlocking kelly bars provide the consistent crowd force needed for deep rock drilling. For kelly bar specifications, see our kelly bar torque ratings guide.
Installation and Maintenance Differences
Bullet and flat teeth use different holder systems and have different maintenance requirements.
Bullet teeth holders:
- B43H: Weld-on holder for B47K series teeth; used on heavy-duty rock augers and buckets
- B85/2: Bolt-on holder for B47K series; allows field replacement without welding
- C30: Weld-on holder for C31HD series teeth; used on large-diameter rock tools
Bullet teeth snap into their holders and are secured by the tooth’s tapered shank. Replacement requires a removal tool or hydraulic press. Inspect bullet teeth every 4 to 8 hours in rock drilling to check for carbide chipping, body wear below the holder lip, and seized rotation.
Want to learn more about the bullet teeth series? Please check out our article on B47K, C31HD, and BK Series Bullet Teeth.
Flat teeth holders:
- Weld-on: The tooth body welds directly to the auger flight or bucket lip
- Bolt-on: The tooth attaches with bolts through a flat mounting plate
Flat teeth are simpler to replace, often requiring only a wrench or grinder. Inspect flat teeth daily in soft ground and every 4 to 8 hours in mixed or abrasive conditions. Watch for edge wear exceeding 50 percent, cracks at the weld, and loss of cutting angle.
Real-World Decision Scenarios
Scenario 1: Mixed Geology (Clay Over Rock)
A foundation crew in the Philippines faced 10 meters of soft clay over weathered limestone at 45 MPa. They started with flat teeth for the clay and switched to B47K22 bullet teeth for the limestone. Cost per pile: 180 in tooling. If they had used bullet points from the surface, the cost would have been 260 per pile, with slower penetration through the clay.
Scenario 2: Pure Rock Formation
A bridge project in Turkey required drilling into limestone at 55 MPa. The crew used B47K22H bullet teeth from the start. Each set lasted 100 meters. Their previous experience with flat teeth in similar rock produced only 25 meters per set. Drilling speed improved by 30 percent, and the total tooth cost dropped from 2.40 per meter to 0.80 per meter.
Scenario 3: Soft Soil Only
A residential piling project in Vietnam involved 20 meters of soft clay with no rock. The crew used flat teeth throughout. Each set lasted over 400 meters. Penetration rate was fast, borehole walls were smooth, and the total tooth cost was under $0.05 per meter. Bullet teeth would have offered no advantage and cost four times as much.
If you want to know a detailed comparison of Bullet Teeth and Roller Bit, please check out our article on Bullet Teeth vs Roller Bit.
FAQ: Bullet Teeth vs Flat Teeth
Can I use bullet teeth in soft soil?
Yes, but it is not cost-effective. Bullet teeth will work in soft soil, but their conical geometry moves less material per rotation than flat teeth. You pay more per tooth and drill more slowly. Flat teeth are the better choice for soft ground.
Do flat teeth work in rock?
Flat teeth can drill through very soft or weathered rock (below 20 MPa), but they wear out quickly in harder formations. In rock above 30 MPa, flat teeth may last only 20 to 40 meters per set compared to 80 to 150 meters for bullet teeth.
How do I know when to switch from flat to bullet teeth?
Use the 30 MPa threshold as your starting point. If your geotechnical report shows rock or dense formations above 30 MPa, plan for bullet teeth at that depth. If flat teeth start wearing out in under 50 meters, that is a field signal to switch to bullet teeth.
Are bullet teeth worth the extra cost?
In rock and hard ground, absolutely. The higher unit cost is offset by longer service life, faster drilling, and fewer changeouts. In soft ground, flat teeth are more cost-effective.
Can I mix bullet and flat teeth on the same tool?
Yes. Hybrid configurations are common on drilling buckets used in mixed geology. Bullet teeth on the outer ring handle harder perimeter material, while flat teeth in the center excavate softer core material efficiently.
Conclusion
The bullet teeth vs flat teeth decision comes down to one factor: ground conditions.
Use the 30 MPa threshold as your primary decision point. Below 30 MPa, flat teeth deliver faster penetration, lower cost per meter, and smoother borehole walls. Above 30 MPa, bullet teeth outperform flat teeth in every metric that matters: service life, drilling speed, and total cost of ownership.
For mixed geology, hybrid configurations give you the best of both worlds. Use flat teeth for soft overburden and switch to bullet teeth when you hit rock. This approach saves money on every pile without sacrificing performance.
If you need help selecting the right tooth for your project, our engineering team can review your geotechnical report and recommend the optimal configuration. Contact Changsha Mingyi for a free tooth selection consultation.
