DTH Drill Rig Buying Guide: 7 Key Factors to Consider
Hole Diameter and Depth Set Every Other Specification
Start with the finished hole. A 90-130 mm blast hole to 20 m is a different machine from a 165-250 mm water well to 200 m. Diameter drives hammer size, and depth drives rod string weight, feed stroke and pull-up capacity. A rig rated for 150 mm at 30 m will not hold 200 mm at 150 m without losing penetration rate and rod life. Write down the maximum diameter and maximum depth you expect in the next three years, not just the first job.
Rock Formation and Hardness
Hard, abrasive rock such as granite or quartzite needs a high pressure hammer and more impact energy per blow. Softer or fractured formations can be drilled with lower pressure and often benefit from a larger bit and higher rotation speed. Abrasiveness matters as much as hardness: it sets bit life and therefore cost per metre. Ask for the rock's uniaxial compressive strength and, if available, a petrographic description before selecting the hammer class.
Air Requirement: Pressure and Free Air Delivery
High pressure DTH hammers typically run at 17-24 bar, with 24 bar becoming common in hard rock. The compressor must deliver that pressure at the hammer's rated free air delivery, plus extra volume to clean the hole. Insufficient bailing air leaves cuttings at the bottom, which re-grinds them and destroys the bit. As a rule, plan for the hammer's rated air consumption plus a margin for hole cleaning and altitude; at 2,000 m elevation, a compressor loses roughly 20 percent of its rated free air delivery. Undersized air is the most common and most expensive mistake in a DTH package.
Feed Force, Rotation Torque and Pull-Up Capacity
Feed force keeps the bit on the rock. Too little and the hammer bounces; too much and you bend rods and wear the bit shank. Rotation torque must turn the string through broken, blocky ground without stalling. Pull-up capacity must lift the full rod string plus the hammer from the deepest hole with margin. Check these three figures against your deepest planned hole, not the average one.
Carrier Type
- Crawler: best on rough, soft or sloping ground; low ground pressure; slower road moves.
- Truck mounted: fast between sites on public roads; needs firm, level ground to set up.
- Wheeled: quick relocation on hard, prepared surfaces such as quarry benches and concrete pads.
Match the carrier to how often you move and over what terrain. Frequent long moves favour truck or wheeled; unstable ground and short moves favour crawler.
Rod Handling and Automation
A mechanised carousel changes rods without a person at the mast. That reduces crew size, removes the most dangerous manual task and shortens each rod change, which matters on deep holes with many rods. Manual handling suits shallow holes and lower capital cost, but it needs a trained, alert crew and adds time per rod. Consider the total cost of the extra crew over the rig's life, not just the purchase price.
After-Sales Support
Confirm parts availability for hammers, bits, shanks and feed components, and ask for the service response time in writing. Operator training is part of the package: correct feed pressure and rotation speed settings protect the bit and the hammer. A rig with no local parts is a stopped project.
Comparing Quotations
Compare the matched package, not the rig alone. Price the rig, compressor, hammer and bits together, and check that the compressor's pressure and free air delivery actually match the hammer at your altitude. A cheaper rig is often the more expensive project when the air package is undersized.
Send Kaishan your hole diameter, depth and rock type, and our engineers will recommend a matched rig, compressor and hammer combination.
Frequently Asked Questions
What air pressure does a DTH hammer need?
Most high pressure DTH hammers operate at roughly 17-24 bar, with 24 bar common in hard rock. The compressor must supply that pressure at the hammer's rated free air delivery, plus extra volume to clean cuttings from the hole. Always check the hammer's published air consumption at your working pressure and add a margin for hole cleaning and site altitude before sizing the compressor.
How do I choose between a crawler and a truck mounted DTH drill rig?
Choose crawler when ground is rough, soft or sloping, because it has low ground pressure and good stability but moves slowly between sites. Choose truck mounted when you move often on public roads and can set up on firm, level ground. Wheeled carriers suit fast relocation on hard, prepared surfaces such as quarry benches. Match the carrier to how often you move and over what terrain.
Why is an undersized air compressor a problem for DTH drilling?
If the compressor cannot deliver the hammer's rated pressure and free air delivery, bailing air is insufficient and cuttings stay at the hole bottom. The bit then re-grinds them, which cuts penetration rate and shortens bit and hammer life. Because the compressor is a large part of the package cost, buyers sometimes reduce it first, but that usually raises cost per metre over the project.
What should I compare when reviewing DTH drill rig quotations?
Compare the matched package: rig, compressor, hammer and bits together. Check that compressor pressure and free air delivery match the hammer at your altitude, that feed force, rotation torque and pull-up capacity suit your deepest hole, and that spare parts and service response are confirmed in writing. A lower rig price with an undersized air package is usually the more expensive project overall.