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Drilling Deep Holes: Things to Keep In Mind

Drilling deep holes is a complicated process. Unless you know the right methods, chances are, you will fail. Read this article to learn more.

Drilling is a cutting method in which a drill is used to make a deep circular hole in the ground or solid materials. When it comes to drilling deep holes, the process can get complicated as it involves precision and expertise.

However, the definitions of drilling are not absolute anymore. The question has changed from how deep the hole is to how to reach greater depths with newer, more advanced, machinery.

Special equipment is necessary to maintain the straightness and tolerances of these holes. Roundness and surface polish are two further factors to consider. The purpose of this article is to explain what drilling deep holes is all about.

What Is Deep Hole Drilling?

A deep hole is defined as possessing a depth-to-diameter ratio of approximately 10:1.

Deep hole drilling is employed in a wide range of industrial applications, but its origins may be traced back to the necessity to drill very precise and straight gun barrels, in which the depth-to-diameter ratio might reach 20:1.

Deep hole drilling necessitates the use of specialized cutting tools, which allow for a greater volume of coolant to be poured into and out of the hole to remove chips.

Many deep hole drilling operations demand the use of specialized machinery to accommodate the specific tools. The machines include two spindles that rotate the workpiece as well as the cutting tool, resulting in exceptionally precise and clean drilling.

Horizontal directional drilling is one of the most efficient and widely used methods of deep drilling used in the construction and energy sector. It gives the drilling experts increased steerability, superior penetration, reduced air requirement, increased durability, and high operational frequency, compared to many other methods of deep drilling.

Horizontal directional drilling products come in many shapes and sizes, depending on the task at hand. Many experts prefer this method of drilling simply because of its efficiency and utility.

As for the basic types in general, deep hole drilling can be classified into 2 versions: BTA drilling and gun drilling. The following sections explain them in more detail.

BTA Drilling

The Boring and Trepanning Association was the first organization to introduce BTA drilling back in the 1940s. The idea behind this method is quite straightforward. A BTA drill is a hollow tool that enables a pressurized coolant to gush into the areas of the hole that are outside of the drill. The chips are evacuated via the hollow chamber within.

An indexable cutter head, connected by a thread, is attached to the hollow tube of the drill when the intended depth of the hole is quite substantial. The effective diameter range of a BTA drill falls between 20 to 200 mm, or 0.9 to 8 inches. However, the drill is capable of perforating holes that are as deep as 400 mm or 16 inches.

Gun Drilling

The introduction of gun drills took the drilling game to a whole new level. This sophisticated method of drilling can reach astonishing depths, as even a depth-to-diameter ratio of 400:1 is possible using this method.

The process of gun drilling involves an elongated and sharp cutting device that is capable of producing extremely accurate and fully linear holes. While this might sound like most other conventional drilling techniques, in reality, the difference in quality is vast.

Gun drills have an internal coolant hole, through which, pressurized coolant is transferred. The chips are taken out via a single flute that is located along the shank. Most small-scale gun drilling projects can be performed on a standard CNC device. However, know that larger projects would require heavier machinery to complete.

Ideal Tips to Follow When Drilling a Deep Hole

Digging a deep hole is not an easy task – regardless of any state-of-the-art machinery that you might possess. On top of that, even if you do attempt to dig a deep hole, there remains the possibility of mistakes happening and ruining the project for good.

Certain deep drilling projects can be so vulnerable, that even the slightest misplacements of the drill can damage the hole and increase costs significantly. The following sections mention some aspects that you should be aware of, before attempting anything significant in your drilling project.

Go Slow on a Deep Drill

When dealing with a deep hole, drills and bits experience intense stress and pressure that seemingly keeps rising as you go further into the material. The best way to approach this is to go slow – agonizingly slow. This will give the equipment time to cool down and will reduce the number of pull outs that you would have to make during the project.

You need to have patience. Drilling gets boring as you go deep. However, if you do not have a firm plan, chances are, the consequences would not be worthwhile. Bits can burn or break off anytime during the drilling.

Although this is quite normal, this happening at greater depths is exponentially more problematic than the same happening near the surface. The deeper your drill is, the more expensive it gets to fix the problems that you face. Thus, slow and careful drilling is the way to go.

Keep the Drilling Equipment Well Maintained

Ensure that all the drilling equipment is properly maintained. The inner tube is where most damages occur over time. Make sure you check the integrity and functionality of specific drill parts like the core case, core spring, bearings, joints, spearhead, latch, and pins.

Check if any of these parts need to be lubricated or cleaned. If it gets difficult to fully clean any of them, try using a degreaser. The more lubricated these devices are, the higher the overall efficiency of the system. The functionalities of these devices are no small feat. Thus, you must keep an eye on their health and usability at all times.

Implement Higher Crowns

Many drilling professionals might suggest you use higher crowns in your drilling project. Although they would not be wrong in suggesting that, as higher crowns reduce the probability of pull outs by a staggering 50 percent, there is a catch in this.

Using a higher crown requires an in-depth understanding of the surface through which you intend to perforate a deep hole. If you do not have that, chances are, in the event of digging multiple holes, none of them would be similar and consistent with each other.

Bit life is also improved when going with a higher crown. Standard transitions can be from 13 mm to a 20 or 26 mm crown.

Avert Deviation

As the hole gets deeper, the possibility of unexpected complexities also goes higher. Deep holes are drilled with a specific target in mind. In most cases, a particular region is intended to be reached. However, if the target is too deep, drill deviation may occur.

This is when the drill diverts from its intended path and takes a slightly new trajectory altogether. This can be an extremely expensive ordeal. It is always better to prevent such mishaps as it saves a ton of time, money, and effort.

Pick the Right Core Bit

Choosing the right core bit is key when it comes to drilling deep holes. In these cases, experts prefer the durability of the drill bit over its effective penetration rate.

Although it all depends on the hardness and rigidity of the surface, full-face crowns tend to improve the lifetime of drill bits. Deeper holes can greatly benefit from this, making life easier for the experts with the task of drilling them.

Choose the Right Rods

Older or imperfectly built rods generally tend to be bent, curved, or simply worn out. However, for an ideal drilling job, the drill rods need to be straight. Unless this is ensured, you would have next to no control over the drilling process as the rod would not hit the right spots despite you aligning everything perfectly.

You need to select the rods carefully as that would determine the quality of your work. Ensure that a high-quality thread compound is being used. Try to select one that contains at least 50% zinc. If not, go for alternatives that are of similar quality levels.

Make Use of Additives

The right additives can make or break your drilling project – especially when it comes to deep holes. Run a mud program even if things look to be going smoothly. Different ground formations have different requirements and need specific forms of additives to ease up.

Additives like polymers and drilling fluids are commonly used in many construction and energy industries around the world.

Final Thoughts

Modern technologies have begun to take deep drilling to a whole new level. These days, artificial intelligence is being used in this process. Do not be surprised if you witness a whole new dynamic of deep drilling in the future.

We believe this article has been able to provide you with a clear idea of how deep drilling works, and the many tips that you can follow to carry out your project with the utmost perfection.

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