How to Make a Deep Hole and What It's For, Which Tools to Use

Deep drilling is a technique to be used only in specific circumstances and with appropriate tools. Usually, these activities take place mainly on construction sites and in mechanical workshops where processing must be subordinated to specific results.

To drill deep holes, however, you can't settle for just any bits: as you can well imagine, you need blades capable of reaching significant depths even on materials difficult to work. Before taking false steps that could ruin your operational course, you can read this article that explains what the best solutions are for you.

What is Deep Drilling and What is it Used For?

Deep drilling is a machining operation necessary for the creation of holes where the depth exceeds at least 10 times the diameter of the tool. It serves to create passages for fluids, structural lightening or fastening seats. This activity requires a tool with specific characteristics and advanced systems to guarantee debris evacuation, cooling and hole precision.

To simplify and alert those responsible, also based on our field experience, we can say that deep drilling is a process in which the variables involved - such as material evacuation, thermal control and hole axis drift - require the operator targeted choices regarding tools and operating parameters. Which, as we'll see in the following paragraphs, are not trivial.

What is Deep Drilling Used For: Useful Sectors

Deep drilling has precise structural requirements. In industrial mechanics and metal processing, this technology produces channels for the lubrication of mechanical sections, creates cooling channels in molds for plastic injection or die casting. The aerospace or automotive industry also uses this technique for different purposes.

In the construction and civil engineering field, however, the need to perform deep holes manifests itself mainly in structural consolidation activities with the insertion of steel bars or anchor ties in foundations and retaining walls. Deep drilling is also used to create passages for technological systems, piping and large-diameter cabling through floors or load-bearing walls.

The Relationship Between Diameter and Depth in Drilling

When can an operation be defined as deep? At the moment when the ratio between the length and the diameter of the hole exceeds a certain threshold. In general terms, deep drilling is spoken of when this ratio exceeds the value of 10:1 in standard mechanical machining, reaching beyond the ratio of 100:1 or even 150:1 with dedicated machines that use BTA/STS tools.

In construction, reference is made to drilling that crosses significant structural thicknesses or that require deep anchor ties. In these cases, however, we must also consider the necessary variants for drilling particularly hard materials, such as the use of a percussion drill and bits for drilling reinforced concrete. Which is always very difficult to work with.

The Tools for Deep Drilling

Everything depends on the context and the work to be carried out. The choice of the tool and the bit for deep drilling is connected to the production volume and the degree of precision required in terms of roughness and geometric tolerance. But also on the required depth. From these considerations you can consider whether to use a normal drill, a CNC machine or a lathe. In the first case, always remember to use helical bits with cross sharpening and special high-strength helix for deep drilling: cobalt models and with TiAlN coating are perfect in these circumstances.

Gun Drills

For example, if with diameters and lengths not too demanding you can use normal helical HSS bits - if you wish with cobalt inserts and/or titanium coating - for higher ratios but still medium diameters you can use gun drills. Here we have a single asymmetric cutting edge and a V-groove that runs along the entire length of the tool.

In the gun drill for deep holes, the coolant is injected at high pressure through an internal channel and pushes the chip outward along the groove. It requires a pilot hole with HSS bit to guarantee correct entry.

Insert Bits

Used on modern machining centers, these bits allow coverage of significant depths without the need for dedicated machines. This happens thanks to the flexibility of hard metal inserts (tungsten carbide) or coated with TiN. Insert bits and interchangeable tip bits can achieve high feed speeds, reducing times in series productions.

BTA Systems (Boring and Trepanning Association)

Ideal for large diameters, to be used only for professional applications. Unlike gun drills, the lubricating fluid is introduced externally, between the tool tube and the hole wall, while chips are forcibly evacuated from inside the tube itself. It is the solution for obtaining large bored shafts and hydromechanical cylinders.

Tools for Deep Drilling in Construction

Overcoming the resistance of heterogeneous and hard materials such as reinforced concrete, natural stone or solid brick requires tools that exploit the combined action of rotation and percussion, or diamond abrasion.

Bits with SDS-Plus and SDS-Max Attachment

For carpentry and heavy fastening, bits with SDS-Max shank and lengths that often exceed 500 mm or 1000 mm are used. The head geometry, often as four cutting edges in solid carbide, is designed to shatter the aggregate and metal reinforcement of concrete without undergoing deviations. The groove promotes the rise of dust and prevents the bit from jamming.

Diamond Crowns and Core Drills

When large diameters are required or when operating on structures with high reinforcement density without transmitting vibrations to the building, core drilling is the mandatory choice. Diamond crowns, mounted on special column motors, remove only a circular ring of material. The system can work dry (with dust extraction) or wet, where water acts as a coolant and transport fluid for drilling mud. This way you can perform deep construction drilling.