How to Choose a DTH Rig for 110–150 mm Blast Holes

Most buyers open the rig catalogue first. In a granite bench that's the wrong end of the problem. Hole diameter decides the hammer and the bit, bench depth decides the rod string and the rig class, and the air package falls out of those two. Pick the rig first and you'll spend the next month hunting for a tool string that fits it.

Here's how the numbers stack up on 110–150 mm bench holes, using published specs from our surface mining rig, hammer, bit and compressor lines.

The hole diameter settles the tool family

A 110–130 mm hole and a 135–150 mm hole are not the same hole. They are a 4-inch hole and a 5-inch hole, and the two families don't share hammers.

**4-inch class (110–130 mm)**

• **K4** — 110–130 mm, working pressure 1.0–2.5 MPa, 31 Hz at 1.7 MPa, 22–35 r/min, air 6/10/15 m³/min, API 2 3/8" REG, 40 kg
• **K40** — 105–130 mm, 1.2–2.0 MPa, ≥31 Hz, 22–35 r/min, air 5/9/14 m³/min, API 2 3/8" REG, 31.5 kg
• **K40C** — 105–130 mm, 1.2–2.0 MPa, 34.5 kg
• **K46** — 105–130 mm, 1.2–2.0 MPa, ≥30 Hz, 34 kg

**5-inch class (135–150 mm)**

• **K5** — 135–165 mm, 1.0–2.5 MPa, 28 Hz, 20–35 r/min, air 7/14/19 m³/min, API 2 3/8" or 3 1/2" REG, 67 kg
• **K50** — 135–165 mm, 1.0–2.5 MPa, 28 Hz, 63 kg

Bits, matched to the same series: K4 bit 105–130 mm, K40 bit 115–150 mm, K50 bit 140–178 mm, K5 bit 135–216 mm.

Two things to read carefully. First, frequency: the K4 strokes 31 Hz at 1.7 MPa while the K5 runs 28 Hz — the 4-inch tool hits faster, the 5-inch hits heavier, which is exactly why the 5-inch family exists at the top of your range. Second, the crossover: the K40 hammer is rated 105–130 mm while the K40 bit is offered 115–150 mm. Where the two ranges overlap you're safe, but if your pattern sits between the 4-inch ceiling at 130 mm and the 5-inch floor at 135 mm, settle the bit diameter against the hammer you actually order before you commit.

Every hammer listed above is high-pressure class. In granite that matters more than it does in softer rock: you want the hammer running at the top of its pressure band, not at the bottom of it.

Bench depth picks the rig class

Bench height plus subdrill is your hole depth, and a rig's rated maximum depth is what it drills **in one pass**, without stopping to add rods. That number is what separates the classes:

A typical granite bench of 15–20 m plus 1.5–2 m of subdrill lands inside a 25 m single-pass class: KG430 at 90–152 mm or KG520 at 105–152 mm, weighing 5,250 kg and 6,500 kg. Go deeper and the weight climbs fast — KT12 drills 115–152 mm to 28 m at 17,500 kg, while KT11 and ZT11 reach 32 m at 90–140 mm and 90–130 mm. That's a haul-road and transport question as much as a drilling one.

A wider hole range is not automatically better. KG430 spans 90–152 mm, but if your pattern is fixed at 115 mm you're paying for range you'll never use.

Size the air from the hammer, then confirm at the rig

Air is where mismatches hide. The hammer tells you the pressure and volume it needs at the face; the rig's specified air demand tells you what the whole package must supply, including the annular return that lifts cuttings out of the hole.

Hammer consumption sits in the tables above: K40 at 5/9/14 m³/min across its 1.2–2.0 MPa band, K4 at 6/10/15, K5 at 7/14/19.

Our own recommended pairings:

Check the pressure your compressor actually holds against the hammer's rated band. K40 works between 1.2 and 2.0 MPa — 12 to 20 bar. An 18 bar machine covers the bottom of that band with margin and the top with barely any; the 21 and 23 bar units are what let a 4-inch or 5-inch hammer run at full pressure in hard granite, which is the whole reason to choose them. Lower-pressure machines exist in the range — KSCY-550/13 at 13 bar and 15 m³/min — and our smaller rigs are paired to them; that's fine for those rigs, but it isn't the package to put behind a K40 in granite.

If the site is at altitude, say so before quoting. Thin air cuts what a diesel compressor can deliver, and the fix is more machine, not a different hammer. Read more on high-altitude drilling.

Rods and the tool string

Rod diameter has to match the hole and the hammer thread:

• **KG420B** — Φ64×3000 mm or Φ76×3000 mm, 3" (K3) / 4" (K4) hammer
• **KG430** — Φ76×2000 mm + Φ76×3000 mm, 4" (K4) hammer
• **KG520** — Φ76×3000 mm or Φ89×3000 mm, 4" (K4) hammer
• **KT12** — Φ76 or Φ89×4000 mm, 4" / 5" hammer
• **KT11** — Φ64 or Φ76×4000 mm, 3" / 4" hammer
• **KT9D** — Φ76×3000 mm, 5" hammer

Stock rod sizes run 76 mm, 89 mm, 102 mm and 114 mm, plus coupling sleeves and shank adapters. Thread is not interchangeable: K40 and K4 carry API 2 3/8" REG, while K5 is offered in 2 3/8" or 3 1/2" REG. Order shank adapters to the hammer's thread, and rods to the string length you need — not the other way round.

Five mistakes worth avoiding

• **Choosing the rig before the hole size.** The rig is the last decision; it has to carry the tool string and the air, not define them.
• **Confusing one-pass depth with total hole depth.** A 25 m rating is a 25 m single-pass rating. Deep benches push you into the 17,000–17,500 kg class for 28–32 m.
• **Reading compressor volume and ignoring pressure.** 19 m³/min at 18 bar and 19 m³/min at 25 bar are different packages for different hammers.
• **Mixing tool families.** A 4-inch hammer under a 5-inch bit is a lost-energy combination. Keep hammer and bit in the same series.
• **Assuming a top hammer will do.** At the bottom of your range it can: KL511 covers 64–127 mm to 25 m with an integrated HC150/HC160 hydraulic rock drill and T45/T51×3660 mm rods at 10 bar working pressure. Past 127 mm you're buying DTH — see top hammer vs DTH drilling.

What to send us

Hole diameter and whether it's fixed or flexible; bench height plus subdrill; rock type; site altitude; and any haul-road limit on machine weight. Those five lines let us point at one rig, one hammer, one bit, one compressor and one rod string instead of a brochure.