DTH Hammer Selection Guide

The hammer is chosen by hole diameter

Each hammer has a working hole range. Choose the hammer whose range covers your diameter with the smallest overlap at the edges — too large a hammer on a small hole wastes air and breaks bits.

That rule sounds simple, and it is the one most often broken. The reason is that hole diameter is not a single number on a real site: it varies with bit wear, with reaming practice and with the ground. A bench specified at 115 mm with reaming may run 125–130 mm in practice, which puts it in a different hammer family. So the first step is not "what hammer covers 115 mm" but "what diameter will the bit actually cut, and how much of the time".

The second thing to understand is what the classification on the nameplate means. Low pressure, mid pressure and high pressure describe the air band the hammer is designed to run in, not its size:

• Low pressure (L2, L2.5): 0.5–0.7 MPa. Small holes, simple air, small compressor. L2 covers 68–88 mm at 5 m³/min.
• Mid pressure (M30C, M3A, M3AK): 0.6–2.5 MPa. Designed for the 90–110 mm band and tolerant of a wide pressure range, which makes them the usual choice where the air package is shared or where pressure at the hammer drops along a long hose.
• High pressure (K3 through K10): 1.0–2.5 MPa, with K80 at 1.7–3.5 MPa and K10 at 1.0–3.0 MPa. These are the production hammers.

The physics matters because it explains why the air consumption figure in the catalogue is a range and not a number. The hammer consumes air in proportion to how fast it cycles; push more pressure into the K5 and it hits harder and faster, consuming more air; reduce pressure and it consumes less, but penetrates more slowly and, in hard rock, starts to polish rather than chip.

Air consumption decides the compressor

The hammer table lists air consumption per model. That figure, plus a margin, is the minimum compressor free air delivery. Working pressure must also be covered — most modern DTH hammers run at 10–25 bar depending on size.

Read the consumption figure at the pressure you intend to work at, not at the bottom of the band. Our published data makes this visible: K3 consumes 4.8 m³/min at 1.0 MPa, 9.6 m³/min at 1.8 MPa and 12.6 m³/min at 2.4 MPa — the same hammer, 2.6 times the air, for the simple reason that a high-pressure hammer cycles faster and each cycle moves more air. If you size your compressor on the low figure and then work at the high figure because the rock demands it, the machine is undersized from the first shift.

Two rules of thumb follow: size for the top of your intended pressure band, then add 10–20% for leakage, hose loss and filter restriction (and more at altitude). A K5 at 19 m³/min plus margin lands in the 21–23 m³/min class, which is exactly where LGCY-21/21-23/18 and LGCY-23/23-25/18 sit.

Our DTH hammer range (published parameters)

Dimensions, connections and working bands

That table carries more information than its size suggests.

Weight is not a marketing figure; it is a handling constraint. A 12 kg L2 can be lifted by hand and swapped at the collar of the hole. A 304 kg K10 needs a crane or a rig with a handling arm, and the rod string behind it must be able to take that weight plus the feed force. If your site has no lifting arrangement for the hammer, you are choosing between hammer models and handling equipment, not just between models.

Length and outside diameter are limits as much as the hole range is. A hammer has to fit inside the hole with clearance for the cuttings to pass; an oversized barrel in a tight hole is a direct cause of stuck strings. That is why the outside diameter column and the hole range have to be read together.

The shank connection column is the single most useful line on the page. Our K4 uses the K4 shank, which is interchangeable with COP44 and DHD340 bits; the K6 uses K6, interchangeable with COP64 and DHD360; K8 uses K8 with COP84 and DHD380. This matters twice: when buying bits, and when a site already owns bits from another supplier. Cross-compatibility is the reason a customer can move to our hammer without scrapping a stock of bits — but it must be confirmed against the shank family, not assumed from the hole diameter. Two hammers that both drill 130 mm holes can take completely different bits.

Bit shank must match the hammer

The bit shank (for example K40, L3) is not interchangeable between hammer families. When you order bits, quote the hammer model and shank so the supplier ships the matching bit.

A shank that is close but wrong will not seat. The failure mode is not a clean refusal to fit: the bit may enter partway, splines may engage on a fraction of their length, and the hammer then works with impact energy transferred through too little contact area. The result is cracked shanks, broken bits and, in bad cases, a bit left at the bottom of a hole. Quote the hammer model and the shank code together, every time, including in reorders.

The same discipline applies to the rod thread. The thread column above runs from square 48×10 on the small hammers through API 2 3/8" REG and 3 1/2" REG to API 5 1/2" REG on the K10. These are not interchangeable, and adapters exist but add a joint to the string and a weak point to the string's alignment.

Choosing inside a band

Within a band, more than one model often covers the same hole diameter, and the choice is about air and duty rather than diameter. Three examples from our own range:

• 90–105 mm: K3 and K30C. Both cover the same holes; K30C asks for more air at low pressure (8.5 m³/min at 1.0 MPa against 4.8 m³/min for the K3) because it is tuned to cycle faster. If your compressor is fixed at the smaller end, K3 is the better match; if you have air to spare and want penetration, K30C uses it.
• 105–130 mm: K4, K40, K40C and K46. K4 has the widest pressure band (1.0–2.5 MPa) and the largest barrel at 985 mm, while the K40 family is shorter and lighter, which suits tight benches and rigs with limited feed travel.
• 195–254 mm: K8 and K80. K8 works at 1.0–2.5 MPa with 12–31 m³/min; K80 shifts the band upward to 1.7–3.5 MPa and 12–35 m³/min for hard rock where the extra pressure converts directly into penetration.

Note the rotation speed and blow rate data that sits behind these figures: the K family runs at 20–35 r/min, while the smaller mid-pressure hammers run 25–40 r/min, and blow rates move from 28 Hz on the K30C and M30C down to 20 Hz on the K10. Slower, heavier blows for bigger holes; faster, lighter blows for smaller ones. Operators who run a small hammer at the rotation speed of a large one destroy bits without understanding why.

Selection steps

• Confirm the hole diameter as it will actually be drilled, including reaming and bit wear.
• Decide the pressure band from the rock: mid pressure for soft and broken ground, high pressure for hard and abrasive rock.
• Read the hammer air consumption at the top of that pressure band.
• Check that your compressor's free air delivery covers it with margin at working pressure.
• Match the bit shank and diameter to the hammer (see the bit guide for face and button choice).
• Confirm the rod diameter and thread against the hammer connection.
• Check handling: weight, lifting arrangement, and whether the rig can feed the hammer and string.
• Plan consumables: bits per hammer, regrinding capacity, spare parts lead time.

Checklist

• Confirm hole diameter and variation. 2) Read hammer air consumption at working pressure. 3) Confirm compressor free air delivery. 4) Match bit shank and bit diameter. 5) Check rod diameter and thread. 6) Plan consumables.

Common mistakes

• Choosing the hammer from the hole diameter alone, without checking the air available at pressure.
• Sizing air from the low end of the consumption range and then working at the high end.
• Buying bits by hole diameter and ignoring the shank code.
• Assuming cross-compatibility between shank families. Our K4 fits COP44/DHD340 bits; a K40 does not.
• Ignoring hammer weight when there is no lifting equipment on site.
• Mixing rotation speeds across hammer sizes without adjusting feed and rotation settings.
• Treating the pressure band as a preference rather than a limit. Below the minimum, buttons polish; above the maximum, seals and shanks fail early.

Conclusion

Pick the hammer by hole diameter, then let rock and air decide the pressure band; the K4 family for 105–130 mm, K5/K50 for 135–165 mm, K6 for 155–190 mm and K8/K80 for 195–254 mm cover the great majority of quarry and open-pit work, while L2 and the M30C/M3A/M3AK mid-pressure hammers handle the small-diameter and low-air situations. Match the shank and thread next, sizing the compressor from the hammer at working pressure with margin. Everything downstream — bits, rods, regrinding schedule — follows from those two decisions.

Next: DTH bit selection for bit shank, face and button selection, best compressor for DTH drilling for the air package, and how to choose a DTH drilling rig for the carrier. Full hammer range: DTH hammers.