5 Things to Know Before Buying 5 Inch DTH Hammer

The wide range of applications and drilling conditions suitable to down-the-hole pneumatic percussion technique requires consideration of more than one type of tool to drill efficiently and profitably.

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Choosing the Correct Hammer

The selection of hammer size is largely determined by the hole diameter and type of rock formation. The optimum blasthole range for DTH drilling is 3½ to 10 inches. Smaller holes are typically drilled with a top hammer rather than DTH hammer, and larger holes generally use the rotary drilling technique, mainly with the focus on hole straightness.

As a general rule, the smallest hole diameter a DTH hammer can drill is its nominal size. A 4-inch hammer is optimally designed to drill a 4-inch hole. The closer the hole diameter is to the hammer&#;s diameter, the more restricted the hole&#;s evacuating airflow is. Drilling holes at the nominal size leaves adequate space for cuttings to evacuate the hole up the annulus between the hammer and drill pipe diameters and the internal diameter of the hole&#;s wall.

Maximum bit size for production drilling is the nominal hammer diameter plus 1 inch. For instance, a 4-inch hammer&#;s maximum bit size is regarded to be 5 inches in diameter. Pipe diameter should be close to the hammer diameter to provide optimum flushing, reducing the chances of getting stuck in the hole.

Pipe (tubes) made from cold-drawn tubing provide a superior surface finish and tolerance compared to tubes made from hot-rolled tubing. A better finish reduces the risk from metal chips from the tubes, called scaling. Scaling that flows through the hammer is a major cause of premature hammer failure.

Friction-welded joints add strength. Heat treating the threads of end-pieces ensures optimum durability and strength of the thread profile. Preserving the thread profile keeps coupling and uncoupling smooth, without adding time to the average rate of penetration.

Selecting the Correct Bit

The bodies of quality bits are precision machined from alloy steel, heat treated to a specified hardness, providing surface compression for fatigue resistance, and then fitted with precision carbide buttons.

Convex-faced, ballistic-button designs are preferable for fastest cuttings removal. This bit design cuts clean with minimal re-crushing, making it ideal for soft to medium, non-abrasive formations.

In hard and abrasive formations, flat-front designs offer best bit life, especially those that feature strong gauge rows with large spherical buttons that are easy to regrind and maintain. An alternative in these conditions is a concave design with spherical buttons.

Concave bit faces work well in medium to hard, fractured formations. In this type of application, a concave bit minimizes hole deviation.

Premium or Economy

A fundamental question is whether one needs a reliable, low-cost hammer or a premium hammer. Buying more than one less-expensive hammer to achieve the same drill feet of a single premium hammer is false economy.

Application Considerations

Manufacturers design DTH hammers to address the challenges presented by the full array of rock types and applications. For deeper hole applications, hammers are designed to work with different air requirements as bailing velocity requirements change.

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Quarrying projects are long-term jobs that will easily outlast the hammer. Frequently replacing hammers would be cost-prohibitive. Dimensional stone quarrying demands consistently straight holes. DTH hammers offer more precision to hole straightness than top hammers.

Mineral exploration generally requires robust hammers capable of running high pressures, often in dirty, remote environments. Operators tend to prefer simple, reliable designs in this application.

Reverse circulation with specialized DTH hammers is less expensive than diamond coring technique. The RC hammers use the same engineered technology and components as standard DTH hammers, but use RC tubes with inner and outer walls for direct airflow to allow the cuttings to pass up through the pipe to a cyclone for collection bags, rather than the typical hole cleaning up the hole&#;s annulus.

Like quarries, open pit mines typically have high equipment utilization, drilling most of the working day.

Some premium hammers for these applications can now be rebuilt twice before replacement.

Properly training drillers to recognize and maintain optimum drilling parameters prevents premature failure of hammers.

Hammer value involves more than component material and design. Additional factors must be taken into consideration. The market offers a range of quality in both economy and premium hammer selections. The hammer must not only be durable enough to be reliable throughout its anticipated lifespan, but its cost of operation figures in. The greater the hammer efficiency, the better the savings in fuel and energy, resulting in lower cost per drilled foot.

Additionally, drillers should consider the manufacturer&#;s product support. A consultation from the manufacturer provides advice on DTH requirements. A knowledgeable product support specialist will also help determine which hammer provides the highest profitability for a project.

Having the right tools for the job is essential for successful water well drilling. Rotary bits can handle soft to medium soil formations. But when you find yourself between a rock and a hard place, you need specialized equipment designed to power through rock formations. 

A down-the-hole hammer may be your solution. If you&#;ve ever (quite literally) hit rock bottom when drilling a water well, you know the value a DTH hammer brings to the table. If you are on the fence about whether a DTH hammer is right for you, consider a few things.

• You can&#;t do some jobs without one. Mud rotary and tricone bits easily drill through soft to medium soil formations, but quartzite, granite, basalt, limestone and sandstone are all too much for standard drill bits. 
• The cost of replacing drill bits adds up. Drag bits and various other bits can wear out prematurely when operators try to use them for applications or rock formations incompatible with that type of bit. 
• You&#;ll need one when it&#;s inconvenient. The nature of water wells is that they tend to be needed in remote or hard-to-access locations. In some instances, gaining access to the water well site is fairly simple. But in most cases, operators won&#;t be traveling on clean, well-paved roads but rather transporting their rig over uneven terrain or unmaintained roads. This is especially true for portable Lone Star drills that are often used to bring water to communities in developing countries &#; far from the nearest supplier. Getting caught in such a location without the proper tool for the job could delay the job for weeks until another bit arrives or result in costly delivery expenses. 
• They&#;re easy to set up. Lone Star&#;s DTH hammer needs only a 185-cfm air compressor to work effectively. Compressors of this size are compact and portable, adding minimal burden to equipment transport. They also happen to be the most common size available at rental centers. Operators can drill even faster with the 3-inch hammer by using it with an air compressor that provides up to 375 cfm.
• They require proper anchoring. For heavy, trailer-mounted rigs, anchoring isn&#;t always necessary. But for compact, lightweight drilling equipment, anchoring stabilizes the drilling platform and helps force drill bits and DTH hammers through soil and rock. Some drills require 30-inch-long anchors for drilling into clay, loamy and sandy soils. If the drill site is on rocky terrain, drillers must find alternative methods for anchoring the drills, such as placing water-filled tanks or barrels packed with rocks onto the unit. This anchoring force is crucial to pushing the DTH hammer, as well as heavy-duty drill bits, through rocky material. 

Lone Star DTH hammers are air-powered with percussive operation, a design that allows the hammer&#;s carbide teeth to methodically shatter rock surfaces. In other words, it&#;s like a small, spinning jackhammer that fits inside a borehole. Aided by the percussive power of the DTH hammer, Lone Star hydraulic rigs can drill as deep as 300 feet through hard rock formations. The DTH hammers, available in 2- 3-, 4-, and 5-inch diameters, are compatible with the full line of hydraulic drills.

Choosing the best drill for a water well is no easy task and matching it closely to the soil conditions can impact efficiency. Work with a manufacturer who will help you choose the ideal rig for your next project and consider a DTH hammer that&#;ll make you ready for rock.

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