How to Choose the Right DTH Hammer and Drill Bit
Hammers and bits are bought to replace out tools, and that is exactly when mistakes get made: the order is placed by diameter and price, and the new tool either does not fit the shank, or fits it and ruins the drilling because it was designed for a different rock or a different air supply. A hammer and bit are part of a matched system: hammer ↔ bit shank ↔ bit design ↔ rods ↔ air supply ↔ rock.
1. Start with the finished hole diameter
Define the diameter you need to hold, not only the nominal size. Gauge wear means a bit that starts at nominal size tends to drill an undersized hole as it wears, which becomes visible when rods, pipes or wire loops no longer pass. Ask for the bit size appropriate to the finished-hole requirement and check resharpening or replacement intervals accordingly.
2. Confirm the shank and connection — before anything else
The bit shank must match the hammer's interface, and the hammer must be matched to the rig and air supply. Compatibility is defined by the shank family (DHD/QL/SD/COP/Mission/NUMA and the various maker-specific families), not by nominal diameter:
- Identify the shank family accepted by your hammer's chuck — the hammer determines what fits, not the bit.
- Do not assume interchangeability from similar-looking splines or from the same nominal size class.
- Check the remaining chain: bit → hammer → rods/adapters → rig, including thread types.
- Two tools can share a diameter range and still not be compatible — the published compatibility matrix for the model is the reference.
3. Match the bit to the rock
| Design element | What it influences | Typical reasoning |
|---|---|---|
| Face shape (flat, convex, concave/drop-centre) | Penetration rate versus straightness control. | Convex and flat faces are generally chosen where directional stability at depth matters; more aggressive profiles are chosen where raw penetration rate dominates. |
| Button shape (spherical, ballistic/parabolic) | Aggressiveness and resistance to button breakage. | Spherical buttons tend to tolerate hard, broken or abrasive rock; more aggressive profiles can drill faster in suitable formations with shorter life. |
| Carbide grade | Wear resistance versus fracture toughness. | Harder carbide resists wear but chips more readily; the right grade depends on rock hardness and impact conditions. |
| Flushing arrangement | Cuttings removal and hole cleaning. | Extra or larger flushing holes help where the air volume is limited or cuttings are coarse. |
| Gauge protection | Holding hole size and avoiding an undergauge hole. | Matters wherever finished-hole tolerance is critical. |
Generalisation has limits: two quarries on "granite" can justify different bit designs. Use observed wear patterns — polished buttons mean the carbide is not failing early but may not be cutting; broken buttons point to too much impact energy or mismatch; rapid gauge wear reduces hole size. Follow the manufacturer's recommendation for the specific formation and verify against results.
4. Verify the air requirement
The hammer has a rated working pressure and an air consumption that rises with pressure and hammer size. Check that your compressor can deliver both — the volume at working pressure, not its rating at atmospheric pressure — plus margin for hose losses, leakage, hole cleaning and altitude. If air is the constraint, a slightly smaller hammer with lower air demand, correctly matched, will out- perform a large hammer that is starved.
5. Monitor wear and record the results
- Record metres drilled per bit, penetration rate, hole condition and the reason the tool was retired.
- Inspect bits and hammers to the manufacturer's procedure, including wear limits and regrinding intervals.
- Replace damaged components rather than running them: one lost button exposes the steel body and can start a cascade of failures.
- Compare alternatives on cost per metre with everything else equal — same rock zone, same rig, same air supply.
Conclusion
Treat rig, hammer, bit, rods and compressor as one matched system. Confirm diameter, shank family, thread and operating requirements before ordering replacements, and keep wear records so the next decision is based on your results rather than on habit.
Related KEENOVA pages
- How to Select a DTH Drilling Rig — the rig and compressor side of the same package.
- DTH Hammer BR, CIR-90 Hammer & Bits.
- DTH Hammer Bits, DHD3.5-90 DTH Drill Bit, Button Drill Bits, Mining Drill Bits.
- Rock Drilling Steel & Button Bits and Tapered Drill Rods.
- Drilling Equipment & Tools.
Send your hammer model, required hole diameter and rock description — ask KEENOVA for the matched hammer and bit.