Drilling Equipment

Drilling is the first unit operation. Learn rotary, down-the-hole (DTH) and top-hammer drilling, bit types, penetration rate factors, drill cycle time, drill productivity per shift, fleet sizing, underground jumbos and longhole rigs, and automation.

Every tonne blasted starts as a drilled hole. Large open pits drill thousands of metres a day with rotary rigs (250–311 mm); underground mines use electro-hydraulic jumbos for development and longhole rigs for stoping. Drill accuracy affects fragmentation, walls and dilution.

An analogy

Choosing a drill is like choosing a power tool: a big rotary rig is a heavy auger for soft-to-medium rock at scale; a top hammer is a hammer drill for small, precise holes.

Drilling methods

Rotary (tricone or drag bits, high pull-down force) for large holes in soft to medium-hard rock. DTH hammers at the bottom of the rod for hard rock and straight holes (100–250 mm). Top-hammer (hydraulic drifters) for smaller holes (≤ 127 mm) and underground.

Penetration rate

Depends on rock strength and abrasivity, bit type and wear, pull-down force, rotation speed, air pressure/flushing. Measure-while-drilling (MWD) logs these to infer rock hardness for blast design.

Underground drills

Face jumbos (1–3 booms, 4–6 m rounds), longhole drills for ring/fan drilling up to 30–50 m, raise-bore machines for vertical openings, and rock bolters.

Automation

Autonomous surface drills (GPS navigation, auto-levelling, auto-drilling) operated remotely; underground jumbos with automated boom positioning to the drill plan improve accuracy and reduce overbreak.

Formulas

• Time per hole: t = L_h / PR × 60 + t_s (min)
• Metres per shift: m = shift h × U × 60/t × L_h
• Drill fleet: N = required metres / metres per drill

Worked example: Drill productivity

Given: PR 30 m/h, holes 17 m, set-up 4 min; 10-h shift, 75 % utilisation

Find: Metres per shift.

• t = 17/30 × 60 + 4 = 38 min/hole
• Holes = 450/38 = 11.8
• m = 11.8 × 17 = 201 m

Answer: ≈ 200 m per shift

Worked example: Fleet size

Given: Need 50 000 m/month; 2 shifts × 30 days

Find: Drills.

• Per drill = 201 × 60 = 12 080 m/month
• N = 50 000/12 080 = 4.1

Answer: 5 drills (4.1 rounded up)

Common mistakes

• Wrong: Ignoring set-up and tramming time. — Right: Non-drilling time often exceeds 30 % of the cycle.
• Wrong: Running worn bits. — Right: Bit wear cuts penetration rate and hole quality.

Applications

• Open-pit production: Rotary and DTH rigs on benches.
• Development: Twin-boom jumbos for drives.
• Exploration & grade control: RC and diamond rigs.

Key takeaways

• Rotary, DTH, top-hammer.
• t = L/PR + set-up.
• Productivity → fleet size.
• Accuracy matters for blasting.

Going further

• Autonomous drilling: Remote multi-rig operation.
• Bit selection: Matching bit to rock UCS and abrasivity.
• Hole deviation: Measurement and correction for longholes.