The three numbers that decide the rig
Hole diameter sets the hammer and bit family. Bench depth sets the rod string and the rig class. Rock hardness sets the required impact energy, which sets the air pressure. Get these three right and the rest of the configuration follows.
Everything else — carrier class, rod string, compressor, bit face, transport method — is downstream of those three. When a DTH spread underperforms on site, the cause is usually that one of the three was estimated rather than measured.
What the rig actually does
In down-the-hole drilling the hammer travels with the bit. The piston strikes the bit directly at the bottom of the hole, so impact energy is not carried through the rod string and does not leak away at every joint the way it does with a top hammer. The rig's job is to hold the hole straight, feed the string with the right force and rotate it, while the compressor supplies the air that drives the piston, flushes the cuttings and cools the bit.
Three consequences follow from that division of labour, and they explain most selection mistakes:
- Penetration rate is set by the hammer and the air supply, not by the carrier. A heavier rig does not drill faster if the hammer is undersized or starved of air.
- Flushing matters as much as impact. If annular air velocity is too low, cuttings are re-drilled instead of lifted, and the extra grinding destroys button life. This is why air demand grows faster than hole diameter: a 4 inch hole and an 8 inch hole differ in area by four times, but the 8 inch hammer family (K8, K80) asks for 12–35 m³/min against 5–15 m³/min for the 4 inch family (K4, K40, K46).
- Rock strength decides how much energy is needed per blow, and therefore pressure. Soft, fractured limestone can be drilled with a mid-pressure hammer at 6–10 bar; hard, abrasive granite wants a high-pressure hammer running at 17–25 bar so that each blow breaks rock instead of polishing it.
The second point is visible in our own range: the 3 inch class hammers (K3, K30C, M30C, M3A) cover 90–110 mm holes and consume 4.8–14 m³/min, while the 10 inch class (K10) covers 254–311 mm at 22–65 m³/min. At that point what changed was the air, not the carrier.
Match the rig to your hole and depth
The table below lists our current open-pit range with published hole range, maximum depth and air demand. Pick the machines whose hole range covers your diameter, then filter by depth.
Our open-pit rig range (published parameters)
| Model | Hole diameter | Max depth | Air demand |
|---|---|---|---|
| KAISHAN KL511 | 64–127 mm | 25 m | — |
| KG430 | 90–152 mm | 25 m | 13.0–20.0 m³/min |
| KG420B | 90–130 mm | 25 m | 10.0–17.0 m³/min |
| KZ5 | 90–115 mm | 21 m | — |
| KT5C | 90–115 mm | 25 m | — |
| KT5H | 90–127 mm | 24 m | — |
| KT11 | 90–140 mm | 32 m | — |
| ZT11 | 90–130 mm | 32 m | — |
| KG520 | 105–152 mm | 25 m | 15.0–22.0 m³/min |
| KZ9 | 115–165 mm | 21 m | — |
| KT12 | 115–152 mm | 28 m | — |
| KT9D | 115–165 mm | 24 m | — |
| KT15C | 140–190 mm | 36 m | — |
| KT25 | 152–203 mm | 35 m | — |
Two notes on reading that table. The air demand column is what the hammer in that hole range consumes; a blank means the machine carries its own compressor. The depth column is single-pass capability.
What each machine carries (published parameters)
| Model | Weight | Engine | Onboard air | Recommended hammer | Rod spec |
|---|---|---|---|---|---|
| KAISHAN KL511 | 17,500 kg | 194 kW | — | HC150/HC160 hydraulic rock drill | T45/T51 × 3660 mm |
| KG420B | 4,150 / 4,350 kg | 58 kW (Yuchai YC4DK80-T302) | — | 3" (K3) / 4" (K4) | Φ64 × 3000 mm or Φ76 × 3000 mm |
| KG430 | 5,250 / 5,700 kg | 73 kW (Yuchai YC4DK100-T304) | — | 4" (K4) | Φ76 × 2000 mm + Φ76 × 3000 mm |
| KG520 | 6,500 / 7,000 kg | 73.5 kW | — | 4" (K4) | Φ76 × 3000 mm or Φ89 × 3000 mm |
| KG550 | 6,200 kg | 73.5 kW | — | K4, K5, K6, K8 | Φ76 / Φ89 / Φ102 mm |
| KG940A | 6,450 / 6,900 kg | 58 kW | — | 3"–6" | Φ76 × 3000 mm |
| KZ5 | 7,900 kg | 73.5 kW | — | 3" (K3) | Φ64 × 3000 mm |
| KT5C | 8,000 kg | 162 kW | 12 m³/min @ 15 bar | 3" | Φ64 × 3000 mm |
| KT5H | 9,500 kg | 162 kW | 13 m³/min @ 18 bar | 3" | Φ64 × 3000 mm |
| KZ9 | 9,300 kg | 86 kW | — | 4" / 5" | Φ76 (Φ89) × 3000 mm |
| ZT11 | 13,000 kg | 235 kW | 18 m³/min @ 22 bar | 3" / 4" | Φ64 / Φ76 × 4000 mm |
| KT9D | 13,000 kg | 295 kW | 20 m³/min @ 22 bar | 5" | Φ76 × 3000 mm |
| KT11 | 17,000 kg | 242 kW | 18 m³/min @ 20 bar | 3" / 4" | Φ64 / Φ76 × 4000 mm |
| KT12 | 17,500 kg | 264 kW | 20 m³/min @ 22 bar | 4" / 5" | Φ76 / Φ89 × 4000 mm |
| KT15C | 24,800 kg | 298 kW | 22 m³/min @ 24 bar | 4" / 5" / 6" | Φ89 / Φ102 × 4000–5000 mm |
| KT25 | 28,100 kg | 372 kW | 31 m³/min @ 25 bar | 5" / 6" | Φ102 / Φ114 / Φ127 × 5000–6000 mm |
| KT30 | 33,930 kg | 563 kW | 36 m³/min @ 35 bar | 8" (K8) | Φ140 × 9000 mm |
This table is where the split/integrated decision is usually settled. Machines with an onboard air end (KT5C through KT30, and the ZT/KZ families where fitted) drill from one unit; the KG family and the KL511 are carriers and need a mobile compressor sized to the hammer.
Weight is the number that surprises buyers. The same hole range can come on a 4.2 t carrier (KG420B) or a 17.5 t integrated machine (KT12). Matching rig weight to haul roads and transport limits is part of the technical choice.
Choosing by hole diameter
The hole diameter you blast is fixed by the fragmentation and loading plan; what you choose is the hammer class that covers it, and that decision transfers directly into the rig. In our range, 90–115 mm is served by KZ5, KT5C and KG420B with the 3 inch hammer class; 90–152 mm is the widest-used band in quarries and small open pits, covered by the KG430 and KT5H; 105–165 mm needs the 4–5 inch class in the KG520, KZ9, KT9D or KT12; 140–203 mm belongs to the KT15C and KT25 with 6 inch hammers; and 195–254 mm is KT30 territory with an 8 inch hammer.
The hole range and the hammer range must overlap by design. If your diameter sits at the very top of a hammer's range, the bit works at its maximum diameter and the machine at the edge of its air budget.
Choosing by bench depth
Depth drives the rod string, and the rod string drives handling time. Up to roughly 25 m most of our open-pit machines drill in a single pass; beyond that the answer is usually more rods rather than a different rig. Two things follow. Rod diameter has to grow with depth to keep the string stiff — our 4 inch class machines run Φ76 mm rods in 3000 mm lengths, while the 6–8 inch class moves to Φ89, Φ102, Φ114 and Φ127 mm in 4000–6000 mm lengths, and KT30 runs Φ140 × 9000 mm. And every joint is a place where alignment and thread wear show up: thread connections are rated for a hammer size, so running a 6 inch hammer on a string specified for 4 inches is a consumable-life problem no operator skill fixes. If depth in your pit is likely to grow, choose the carrier on the depth you expect in three years.
Choosing by rock
Rock enters the decision twice: through hardness, which sets working pressure, and through abrasiveness, which sets bit face and regrinding interval.
- Hard, abrasive rock (granite, basalt, quartz-bearing porphyry): high-pressure hammer class. The K family runs 10–25 bar, with K80 at 17–35 bar and K10 at 10–30 bar, so each blow chips rock instead of dusting it.
- Medium rock (limestone, sandstone, most marble): mid-pressure hammers such as M3A, M3AK and M30C at 6 bar and above cover 90–110 mm holes at 5.5–12 m³/min, which keeps the compressor small and the fuel bill low.
- Soft, broken or weathered ground (L2 class, 68–88 mm, 5 m³/min at 5 bar): low pressure is enough; forcing a high-pressure hammer into weak rock mainly produces deviation and over-drilling.
Abrasiveness decides how often you pull the string: a flat button polishes rather than breaks, so the figure that matters is metres between regrinds, from your own records.
Tooling and air are part of the same decision
A rig without the right hammer, bit, rod and compressor is not a working system. Once the rig is chosen, size the compressor to the hammer air consumption, not to the rig.
Only two of those three pairings are usually checked at the buying stage, and the one that gets skipped — hammer consumption against compressor delivery — decides whether the rig ever reaches its rated penetration rate. The full sizing method is in our guide to choosing a compressor.
Selection steps, in order
- Fix hole diameter and its expected variation (bit wear, reaming, ground conditions).
- Fix bench depth and the drilling pattern you will run.
- Name the rock type and its hardness and abrasiveness.
- Convert your production target into holes per day, then into metres per hour — that number tells you how much rig and how much air you actually need.
- Decide split or integrated: integrated if the rig moves between benches weekly, split if a compressor can be shared across rigs.
- Size the air package from the hammer consumption at working pressure, then add margin.
- Confirm the consumable chain: hammer model, bit shank and diameter, rod diameter and thread.
- Check the site and the service chain: altitude, temperature, access roads, transport weight, and who supplies bits, rods and hammer spares.
Common mistakes
- Sizing the compressor from the rig's air connection rather than from the hammer's consumption figure.
- Running an oversize hammer in a small hole. It wastes air, breaks bits and does not improve penetration.
- Mixing shanks. Bit shank, hammer and rod thread must belong to the same family.
- Buying the machine without a consumables plan. Bits and rods are the recurring cost; on a long import lead time, the site stops before the machine wears out.
Checklist before you order
- Hole diameter and expected variation. 2) Bench depth and drilling pattern. 3) Rock type and hardness. 4) Required metres or holes per day. 5) Altitude and site conditions. 6) Whether you already own a compressor. 7) Rod and bit consumables plan.
Where to go next
- Best compressor for DTH drilling — how to size the air package to the hammer
- DTH hammer selection guide — hole ranges, air consumption, shanks
- DTH bit selection — shank, diameter, face and buttons
- Drilling cost per metre — what actually drives your cost
- Open-pit mining drilling, quarry drilling and high-altitude drilling — configurations by application
- Surface mining drilling rigs — the full open-pit range
Conclusion
Choose the hammer family from the hole diameter, the rod string and carrier class from the depth, and the pressure from the rock. Then size the air package from the hammer, not from the rig, and treat the consumable chain — bit shank, rod thread, regrinding capacity — as part of the same purchase. The KG430, KG520 and KT11 fall in the 90–152 mm band where most quarry and open-pit work happens; the KT15C and KT25 take over above 140 mm, and the KL511 covers the small-diameter band. Send us the hole diameter, depth and rock type and we will size the whole system as one package.