What is Deep Hole Drilling? Process, Tools, & Applications 

Deep hole drilling 

In the manufacturing industry, any drilled hole with a depth-to-diameter ratio greater than 1 is referred to as a deep hole. Heat exchangers, fuel rails, hydraulic systems, and many other mechanical products need deep holes for their functionality. 

With standard drilling bits used in CNC Drlling Services, you can not drill these types of engineering holes. Regular bits struggle to reach the desired depth. Therefore, specialized tooling, such as gun drilling and BTA drilling, is used to create the deep holes. 

Furthermore, we will discuss the deep hole drilling process, required tools, variations of drilling machines, and where deep holes are used.

What is Deep Hole Drilling? 

First, let’s start with the definition of drilling: it is the process of creating holes, where a rotating drill bit enters from the surface and removes material until the desired depth is achieved. Typically, the diameter of the hole matches the corresponding drill bit size. Now, when is the hole called deep? It is called a deep hole if the depth is more than 10 times the diameter. 

The deep hole drilling is different from regular drilling as it needs pressureized coolant flow in the machining area continuously. The exact chip removal mechanism depends on the type of tooling used in the proces. 

Carbide drills with spiral flutes are a common choice for drilling deep holes. They offer both sharp cutting edges and effective coolant reach.

. 

The Deep Hole Drilling Process

The deep hole drilling process works by rotating the tool (or both the workpiece and the tool), while the sharp tip penetrates the material of the workpiece. Then, the rotating deep hole drilling tools continue to move downward until the desired depth is achieved.

Steps of the deep hole drilling process are;

1. 1. Tool Selection and Setup: Clamp the chosen shape and size of tool on the spindle and work on the machine bed. Also, align the workpiece and the hole drilling tool before running the machine.
   2. Tool or Workpiece Rotation: As the CNC program runs, either the tool or the workpiece starts to rotate. 
   3. Coolant Apply: Application of a high-pressure coolant removes the chips and counters the heat buildup.

• Steady Advance of Drill: The drill tool advances deep into the material at a steady rate, removing the material and creating the desired hole. 

Deep Hole Drilling Machines 

Gun drilling and STS are two types of machines for deep hole drilling. They have a distinct chip removal mechanism and can create holes of various sizes. 

Gun Drills or Gun Drilling 

Unlike twist carbide drills, gun drills are a thin tool with a straight, full-edge: this tool provides greater accuracy and efficiency over the traditional method. You can drill deep holes up to 50 mm in diameter and a 20:1 depth-to-diameter ratio.

Gun drilling machines are used in mold toolings, medical components, automotive fuel systems, and many other applications that require deep and straight holes.  

STS/BTA Drilling

STS refers to a single tube system, in which the coolant is applied through the hole inside the tool. The tool also features grooves outside the tool, extending across its length, and chips are removed from these grooves. 

Chip evacuation is the main challenge in drilling deep holes. The design of STS enables efficient evacuation and allows for higher depths. You can drill holes up to 200mm in diameter with the STS drilling system. This deep hole machining is mainly suitable for hydraulic systems, turbine shafts, and coolant channels in industrial components.

If you are confused about which one is best for your project, you can contact the experts in the industry, like ProleanTech, where you can get insights from professionals to refine your project outcomes. 

Applications of Deep Holes  

Industries like automotive, energy, die & tooling, medical, and electronics require various components with deep holes. The table below outlines applications in various industries, along with relevant examples. 

Conclusion

Deep hole drilling is a crucial machining process in manufacturing, requiring the careful selection of machines and tools, as well as precise drilling parameters. Additionally, a high level of expertise is required to counter challenges such as chip evacuation, coolant flow, and runout.

You can choose between STS and gun drilling, depending on the hole diameter, depth, and the ratio between them. STS is more favourable for large and deep holes. 

FAQs

What is a deep hole drilling?

The machining process that creates holes with a depth greater than 10 times its diameter (D> 10x D) is called deep hole drilling. 

What type of drill is used for deep holes?

Specialized tools, such as gun drills and BTA/STS systems, are used to drill deep holes. Gun drill is suitable for small diameters, and BTS works best for deeper and larger diameter holes. 

Is gun drilling the same as deep hole drilling?

Yes, gun drilling is a type of deep-hole drilling that can create long, small-to-medium diameter bores (typically ~1–40 mm).

What is the drilling technique commonly used when drilling deep holes?

Gun drilling and BTS/STS (single tube system) are two commonly used techniques for drilling deep holes.

What is the best drill bit for deep holes in wood?

Although long-flute ship augers are standard for wood drilling, the exact type of tool to drill a deep hole in wood depends on the size of the hole and other requirements. 

How accurate is a gun drill?

A gun drill can make deep holes with high straightness and accuracy down to ±0.0076 mm.