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deep hole drilling

Everything You Should Know About Deep Hole Drilling

Deep hole drilling is a popular metal-working process in many fields, especially in producing firearms or heavy ordinances. This operation is perfect for most high-precision drilling projects because it provides highly accurate, repeatable holes with superior surface finishes. Therefore, it is crucial to understand everything about deep hole drilling to achieve the best results.

This guide discusses everything you need to know about deep hole drilling, its benefits, applications, and standard techniques. You’ll also learn helpful tips for effective deep-hole drilling. Let’s dive in!

What Is Deep Hole Drilling?

what is deep hole drilling
What Is Deep Hole Drilling?

Deep hole drilling is a process of machining a hole ten times deeper than the hole diameter. A deep hole is characterized by at least a depth-to-diameter ratio of up to 10:1. It is suitable for creating holes of desired depth in different CNC machining materials ranging from aluminum to the strongest super-alloys.

Deep hole drilling is a widely used technique in many industry applications. However, it originated from the need to drill straight gun barrels with high accuracy in which the required depth-to-diameter ratio can reach 20:1.

Later on, the technology advanced and extended to other applications, including making automotive parts like cam-shafts, crank-shafts, fuel rail, and fuel injector bodies, creating lo holes in injection molding, aerospace parts like landing gear, different parts in the oil and gas sector, general engineering components like hydraulic cylinders, etc.

Importance of Deep Hole Drilling in Modern Industries

medical device deep hole drilling
Medical Device Deep Hole Drilling

Modern industries like aerospace benefit a great deal from deep-hole drilling. Here are the typical roles this operation plays in respective applications:

Aerospace and Defense

Deep hole drilling techniques offer the tight tolerances and high accuracy required in machining aerospace components such as landing gear and turbine blades. Deep drilling processes produce holes exactly to tolerances to ensure optimal performance and low weight of these components.

Meanwhile, the defense industry is another primary field where deep-hole drilling is widely embraced. Manufacturers in this field use this drilling strategy to make accurate holes in the gun barrel with the preferred surface finish.

Automotive Applications

Engineers and product designers in the automotive field rely on deep-hole drilling to achieve preferred tolerances in machining automotive parts and components. For instance, the fuel injectors in vehicle engines require small and highly accurate holes to inject fuel into the combustion chamber efficiently. Also, the crankshafts and cylinder blocks require precise deep holes to function effectively.

Also, deep-hole drilling is pivotal in machining hydraulic cylinders for engineering vehicles and other industrial applications. These hydraulic cylinders are crucial for bulldozers, forklifts, excavators, etc. Deep hole drilling is ideal for making holes with the desired precision to ensure seamless motion.

Oil & Gas Exploration

custom deep hole drilled petroleum logging instruments
Custom Deep Hole Drilled Petroleum Logging Instruments

The oil and gas industry benefits from deep-hole drilling because it helps make boreholes for oil and gas extraction. The process offers extreme depth-to-diameter ratios in long workpieces without compromising wall thickness or accuracy in roundness. Deep hole drilling is perfect for making holes with a depth-to-diameter ratio of up to 20:1.

Key Benefits of Deep Hole Drilling

deep hole drilling machine
Deep Hole Drilling Machine

Below are some of the common benefits of deep hole operations:

Precision and Accuracy

Since deep hole drilling operations are automated, they allow precise and accurate depth-to-diameter ratios in drilled holes. Hence, deep drilling is ideal for attaining holes with dimensions that are exact to requirements in industries such as aerospace and defense.

Improved Surface Finish

Deep hole drilling processes offer a better surface finish than conventional methods done with twist drills. Deep drilling involves the use of specialized tools and setups for high-pressure coolant flow and effective chip evacuation, ensuring the superior surface quality of the hole. Consequently, this excellent surface finish mitigates friction and wear, ensuring the durability and proper performance of moving parts.

Enhanced Tool Life

The tools used in deep-hole drilling are usually durable since they are made of super-strong materials and have unique geometries. As such, these tools can withstand wear and prevent consistent tool changes. Hence, the extended tool life of deep-hole drilling machines helps to save costs while ensuring peak productivity.

Common Techniques in Deep Hole Drilling

deep hole drill principle
Deep Hole Drill Principle

Product manufacturers and designers rely on different deep-hole drilling processes to achieve superior-quality final products while controlling costs. This section discusses the standard techniques used in deep hole drilling:

Gun Drilling process

gun drilling bta drilling
Gun Drilling & BTA Drilling

This deep-hole drilling method uses a machine with a thin cutting tool to achieve highly accurate and straighter holes in a workpiece. The introduction of gun drills transformed the drilling game because they offer higher accuracy than conventional-style drills.

The gun drill comprises a straight flute cutting edge and a single internal coolant hole. As such, you can supply pressurized coolant through the inner holes while you remove chips through the single-flute gun drills within the shank. Hence, material removal occurs at the same time as the drilling.

However, you might be able to perform the deep hole operations with a standard CNC gun drilling machine, depending on the hole’s depth-to-diameter ratio. However, you can use special tools to achieve higher precision. A specialized deep-hole drilling system can achieve larger diameters of about 400:1.

BTA Drilling

The Boring and Trepanning Association introduced the BTA drilling in the 1940s. This process involves inserting a special hollow tooling in the hole pushing pressurized coolant into the hole on the outside of the drilling tool during the operation. Then, it removes the chips through the hole within the drill.

Besides, the BTA tooling or single tube system comprises a hollow drill tube fastened to a threaded indexable cutter head, depending on the diameter and depth of the hole that requires drilling. The diameter range of the BTA tools ranges from 0.80 – 8.00 inches (20 – 200mm) and can attain depths of about 16.00 inches (400mm).

Ejector Drilling

Ejector drilling or a double-tube system is often used on machining centers and conventional machine tools. It provides drilling depths of about 100 x D. Despite being a BTA drilling system variant; it has no sealing to prevent the metal-working fluid at the workpiece from exiting. Therefore, this drilling technique is suitable for oblique boring or discontinuous parts since covering up the metal-working fluid circuit is impossible.

Moreover, you must feed the metal-working fluid through an annular space between the inner and drill tubes. Then, the fluid comes out from the side of the drilling head, flowing over the drill head to cool and lubricate it. The fluid pushes the chip through the internal cavity of the inner drill rod for efficient removal. Introducing some of the fluid into the thinner tube ring nozzle would be best.

Considerations for Tools and Equipment for Deep Hole Drilling

deep hole drilled petroleum logging instruments parts
Deep Hole Drilled Petroleum Logging Instruments Parts

Deep hole drilling can be quite complex, irrespective of the sophistication of the machinery. Also, there are higher chances of errors when drilling a deep hole. However, here are some helpful considerations for effective hole drilling:

Choosing the Right Drill Bit

Using the appropriate drill bit to drill straight holes is essential to avoid drill deviation or inaccuracies. Drilling deep holes with incompatible drill bits can result in expensive mishaps. As such, manufacturing experts often prioritize the drill bit’s compatibility and durability.

However, full-face crown drill bits exhibit improved lifespan even though it is subjected to the hardness and rigidity of the material’s surface. Therefore, it is advisable to use the right drill bits to drill precise and accurate holes easily.

Importance of Coolants

Coolants are crucial in deep hole drilling because they ensure proper cooling and lubrication of the hole drilling operation. These coolants help to maintain moderate temperatures, ensuring longer tool life.

These high-pressure coolants are also responsible for efficient chip evacuation from the cutting zone, preventing surface damage and chip removal strokes that may take time. Coolants allow the drilling process’s productivity and improve the hole quality.

Modern Innovative Equipment

Manufacturers often use specialized equipment designed explicitly for deep-hole drilling procedures. These innovative equipment are set up to optimize the hole drilling operation for straightness and efficiency.

The technological advancement of drilling equipment allows you to attain a certain depth-to-diameter ratio since a computer controls the process. Similarly, there are different deep-hole drilling techniques with varying modes of operation. Hence, choosing the one that fits your project demands best is essential.

Challenges and Solutions in Deep Hole Drilling

deep hole drilling cutter
Deep Hole Drilling Cutter

Here are some of the challenges you may encounter during deep hole drilling operations and helpful ways to overcome them:

Avoiding Common Mistakes

Machinists often encounter common mistakes like misalignment or drill bit incompatibility, resulting in scrapped parts, poor surface finish, and excessive machine tool wear. Consequently, you may have to incur additional machining costs and experience delayed production.

Solution: Partner with a service provider with vast knowledge of the techniques and tools used in deep-hole drilling. Similarly, it is advisable to implement process documentation and quality control measures to mitigate human errors and detect mistakes early.

Ensuring Workpiece Stability

Deep hole drilling is a complex metalworking process that involves making long, straight holes in components. As such, workpiece deflection can occur when the workpiece is not properly held in position, resulting in inaccuracies. Therefore, it would be best to ensure workpiece stability when making holes.

Solution: Use special fixturing mechanisms to steady the workpiece, mitigate deflection, and ensure drilling accuracy. Also, it is advisable to plan the drill entry point carefully to reduce impact and mitigate chances of deflection.

Overcoming Material Challenges

Although deep hole drilling has extensive material compatibility, each material poses challenges. Certain materials, such as plastics, may experience deformation, while rigid materials like titanium may cause consistent machine tool wear during deep hole drilling.

Solution: Using drill bits with the correct geometry, material, and coating on the workpiece material would be best to avert this challenge. You can use drill bits with solid carbide or diamond coatings for better wear resistance. However, optimize feed rates, speed, and coolant selection to mitigate heat and ensure proper cutting frequency.

Why Choose AT-Machining for Your Deep Hole Drilling Needs?

at machining metal cnc machining service 1
Your One-Stop CNC Machining Services From China

AT-Machining is the right machining partner for your CNC and deep-hole drilling needs. We leverage our range of hole-drilling machines with our machinists and product engineer expertise to achieve preferred tolerances and outstanding accuracy in your final products and prototype machining. We have years of experience offering reliable deep-hole drilling services across all fields.

As your trusted manufacturing partner, we are committed to serving you superior quality products with high precision at cost-effective prices. Our quality control experts ensure your products meet strict quality standards. We promise expert machining solutions within the shortest possible time.

Experience our cost-effective and reliable machining services as we handle your next project! Our clients have enjoyed long-term partnerships as we consistently offer expert solutions. We are a top custom parts manufacturer, deep hole drilling services, and surface finishes provider across different sectors.


Deep hole drilling is a versatile process that benefits various applications with stringent requirements and unique challenges in machining rigid materials with tight tolerances. This operation offers the preferred depth-to-diameter ratio for your hole-drilling projects. However, it would help to understand everything about the process to effectively exploit its benefits in achieving high-quality products.

FAQs about Deep Hole Drilling

How Does Deep Hole Drilling Differ from Drilling?

Deep-hole drilling differs from regular drilling since cooling lubricant must be passed to the cutting edges in high volume and under high pressure, depending on the intended drilling technique and diameters.

What Is the Best Drill Bit for Drilling Deep Holes in Wood?

The typical drill bits for making deep holes in wood are Auger bits. These drill bits have a helical or spiral shape and comprise a sharp point on their tip, allowing drilling efficiency. This tip efficiently pulls the bit through the drilled wood to achieve the preferred depth.

What Is the Standard Ratio for Deep Hole Drilling?

Generally, a normal drilling process has a length-to-diameter ratio usually smaller than 5. Hence, deep-hole drilling is characterized by a length-to-diameter ratio greater than 5.

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