Rock Drills: Drilling Anchor and Blast Holes in Hard Material

A rock drill is not a hammer with a bit on it. It combines percussion - the hammer blow that fractures material at the bit face - with rotation, which indexes the bit so each blow lands on fresh material. Get the balance wrong and you either polish the hole or snap steels.

We build the KT-RD75 in the 65 lb class, and stock parts for 30 lb, 60 lb and 65 lb class drills.

What rock drills are for

• Anchor holes in concrete and rock - guardrail posts, tie-backs, rock bolts, foundation anchors.
• Blast holes in quarry and excavation work.
• Dowel holes for slab tie-ins and structural repair.
• Utility and pole work where the ground is rock rather than soil.
• Foundation and underpinning work in hard material.

If the material is soil or clay, you want a clay digger, not a rock drill - see the KT-CD series. Rock drills are for material that fractures.

Flushing: the part that decides everything

Cuttings have to come out of the hole. If they do not, the bit grinds the same material repeatedly, penetration collapses, and heat destroys the bit.

Air flushing blows cuttings out through the drill steel. Simple, effective, and it generates dust - which in concrete or silica-bearing rock is a serious respiratory hazard requiring control.

Water flushing carries cuttings out as slurry and suppresses dust at the source. Slower to set up, and it makes a mess, but it is frequently the compliant option and it is easier on bits.

Dust collection is the third path - capture at the hole. We stock dust collection equipment for exactly this.

Whichever you use: if penetration rate drops suddenly, check flushing before you check anything else. It is the cause far more often than the tool.

Steels and bits

Drill steel is a system - shank, rod and bit have to match the drill and each other.

• Keep bits sharp. A dull bit does not just drill slowly; it transmits shock back into the steel and the drill, and that is how you break things.
• Retire bent steels. A bent rod puts the blow off-axis, wears the chuck, and will eventually snap.
• Match length to the hole. Excess length flexes and wastes energy.
• Inspect shanks for mushrooming and cracking every shift.

Technique

Collar the hole carefully. Start slow, at reduced percussion, until the bit is seated. Starting at full power lets the bit wander and can snap a steel.

Keep the drill aligned. Once the hole is started, the drill has to follow it. Forcing an angle binds the steel.

Steady feed pressure. Too little and the bit bounces without cutting; too much and you stall rotation and bind. The tool tells you - listen to it.

Back out periodically in deep holes to clear cuttings.

Air supply

Rock drills are among the highest CFM consumers on any job, and flushing air is on top of the drilling air. Size the compressor for the drill plus flushing, use adequate hose ID, and expect a marginal compressor to cost you real penetration rate.

Safety

Silica dust is the significant hazard here and it requires engineering controls - wet drilling or dust collection - plus respiratory protection. Hearing protection and eye protection are mandatory. Watch hand placement around rotating steel, and keep bystanders clear of the flushing path.

Browse rock drills and parts by class: 30 lb, 60 lb, 65 lb.