Top hammer drilling vs. Down-the-hole drilling


Top hammer vs. DTH Drilling

If you’re considering buying a new rock drill for your project or company, there are a number of things to take into consideration before taking the plunge. Rock and mining site conditions, budgets, anticipated future projects, noise, desired hole dimensions, existing equipment and available time are all factors that you should take into account before making that purchase. We’re going to outline some of the major differences between top hammer, or drifter drills, and down-the-hole, in-the-hole, or DTH drills.

The mechanical difference between the two types of drills is where the hammer is situated in the machine. The hammers applying repeated percussive pressure to the drill bits of DTH drills are situated in direct contact with the bit, and are thus actually ‘down-the-hole’. Top hammer drills, however, apply that pressure at the top of the drill string, outside of the hole.

sandvik rock drill di600 Sandvik DP1500 rock drill

While the main overall difference between the two technologies is that DTH drills are more accurate and efficient at depths over 20 m deep and more versatile, the other considerations are very important – like the fact that DTH drills are typically more expensive. Both types of drill can be used in soft, medium and hard rock but DTHs perform better in very hard rock, especially fractured hard rock. Neither drill, however, is an excellent performer in soft rock, when a rotary drill should be considered.

DTH drills are more energy-efficient as far less energy is lost in the transmission of force from the hammer to the drill bit. In top hammer drills, some energy is lost via its path down the drill string. This continual pressure from the hammer on the rods and couplings of top hammer drill strings wear those parts down over time, meaning that top hammer drills require more replacement of consumables in the long run. Because the hammer is outside the hole while drilling, top hammer drills make much more noise onsite than DTHs. While this noise can be reduced by adding a cab to a top hammer drill, this will increase the price. DTH drills are much quieter as the repeated percussion of the hammer is located in the hole.

Rockmore DTH hammer

Top hammer drills are well-suited to smaller, shallower holes (up to 20 m), drilling more quickly and efficiently than DTHs in such conditions. One drawback of DTH drills is that they have a minimum hole diameter of about 3 ½ in, while top hammer drills can drill holes with diameters from 2 in. However, for much wider holes – even up to 30 m- DTH drills can be used to create a pilot hole which can then be reamed further to the desired diameter.

The accuracy of top hammer drills pales in comparison to the highly accurate DTHs but drill tubes can improve this and reduce the deviance of top hammer drilling. Top hammer drills can also jam and lose a great deal of accuracy in hard rock, especially fractured hard rock, and are not recommended for this application. If you’re looking for accuracy at depth, especially in fractured hard rock, DTH is the way to go.

Sandvik drifter hl1010

From the specifications, it is obvious that DTH drills are much more versatile than top hammer drills. However, versatility comes at a price – slower drilling at less than 20 m deep and a higher capital cost. It’s also vital to consider what other applications you may require the drill for. If your site or anticipated future projects include conditions that can be effectively drilled with a top hammer drill, you could save a huge amount on capital costs by selecting a drifter/top hammer.

Our experts at Recon Drills are qualified and experienced in assisting clients with selecting the perfect drill for their company or specific applications. We understand that every site is different and every client has unique factors to consider when purchasing a drill. Get in touch with us and we’ll analyze your needs and budget to find the best solution.