A drill rod is a common term in the machinery and manufacturing industries. You can use drill rods to manufacture various tools such as cutters, hot-work tools, machine parts, punches, files, and more. But, do we know how to choose the right drill rod for our needs?

Drill rods differentiate in regards to toughness, durability, temperature resistance, and applications. With so many different material grades and types to choose from, how do we ensure we choose the correct drill rod?

That’s where we come in – this is the only guide you’ll ever need to drill rods, their uses, and applications. This guide is suitable for complete beginners as well as professionals in the industry.

Let’s see some of the most frequently asked questions on the subject of drill rods!

What Is a Drill Rod?

Simply put, a drill rod is a lengthier steel piece of easy-to-mold tool steel that you can use for machining to produce different tools and parts.

Typically, drill rods are round. However, there are some square ones, such as the square kellys you’ll see below. Drill rods are generally soft enough to be machined into their final form.

Drill rods need to have a clean and smooth surface. To manufacture them in this way, we usually use precision grinding.

What Is a Drill Rod Used For?

Drill rods have many different applications. Producers usually use drill rods for manufacturing drilling bits, shafts, dowel pins, reamers, punches, taps, hammers, files, cutting tools, hot-work tools, etc.

Different grades of drill rods are best suited for specific uses. For example:

W1 is suitable for cold-work tools, hand-held tools, cutting tools, punches, dies, etc.;

O1 grade is best for punches, dies, and gages;

A2 and D2 can be suitable for hobs, rolls, knurls, coining dies, punches, dies, etc.;

S7 gade is perfect for knock-out pins, drift pins, stamps, grippers, track tools, river sets, mandrels, circular pipe cutters, and more;

H13 (or V44) is suitable for hot-work tools, plastic molds, die-casting tools, core pins, ejector pins, and more;

Types of Drill Rods According to the Manufacturing Process

According to the manufacturing process they go through, there are three different types of drill rods: air-hardening, water-hardening, and oil-hardening. Each of these drill rods has various uses and applications. Let’s explain something about each of these different types of manufacturing processes and drill rods & casing.

Air-Hardening

We’re starting from the toughest category of tool steel – the air-hardened drill rod. Air-hardened steel has more alloy, and this is what makes it so hard and resistant. After heat treatment, you can leave air-hardening types of drill rods to harden in still air.

Air-hardening drill rods have superior machinability and wear resistance when compared to oil or water-hardening rods. Furthermore, air-hardening is safer than water or oil-hardening in regards to distortion and dimensional stability.

Oil-Hardening

Oil-hardening drill rods are second in line when it comes to their hardness and durability. Although oil-hardening rods have less alloy than air-hardening rods, they’re still rich enough to withstand welding. On top of that, oil-hardening steel is suitable for machining.

If you’re not sure what the term “oil-hardening” means, it implies heating the rod until it’s glowing red and then dipping it into a pool of warm oil. With this, the steel becomes hard and ready for machining or welding.

Water-Hardening

And finally, we have the water-hardening drill rods, which portray the lowest alloy content but are excellent for machining. However, they’re deficient in alloy content, which signifies that they’re not structurally suitable for welding purposes.

To harden a drill rod with water, we first heat the steel until it becomes glowing red, and then we plunge it into a pool of water to cool off. Once the metal is hard, it can be easily machined but not welded. You can usually use water-hardening drill rods for the manufacturing of files or hammers.

Types of Drill Rods According to Different Threads

We can classify drill rods into three different types according to different threads: ordinary drilling rigs, square kelly rods, and heavy-weight drill pipes.

The Ordinary Drill Rod

We can easily recognize the ordinary drill rod since it’s the central or basic part of the drill stem. At the top, the ordinary drill rod connects to the square kelly (explained below), and at the bottom, it’s attached to the drill collar.

In borehole digging, the function of the ordinary drill rod is to deepen the hole, transmit torque, and move the drill up and down.

Drill Bit Material Types & Coating – Types of Drill Bits

1. Carbon Steel Drill Bit

– Low carbon steel: this is the cheapest option for making a drill bit, due to their poor tempers, low carbon steel drill bits are usually used for drilling softwood and some plastics, and require to be sharpened often to extend the lifespan.

– High carbon steel: a better material than low carbon steel, high carbon steel drill bit can keep their shape and effectiveness longer, so it can be used to cut stronger materials, like hardwood and soft metals.

2. High Speed Steel Drill Bit

Compared with carbon steel bits, high-speed steel drill bit is a more popular choice on the market now. HSS is a special type of carbon steel, maintaining structural integrity while bearing high temperature is a marking advantage of the HSS drill bit, what’s more, high speed steel bit has higher wear resistance and hardness, it can also work well at a normal temperature. HSS drill bits are suitable for most of the wood and metal drilling process, including CNC drilling. Titanium nitride and other types of coatings can be applied on the HSS tool to increase lubricity and reduce friction.

3. Titanium Coated Drill Bit

Titanium is not only a popular aerospace and medical material, but also a versatile drill bit coating material, which can make the drill bit last longer. Due to its high corrosion resistance, good fatigue limit, heat limit, relatively light weight, and longer service life, titanium coated drill bit is perfect for repetitive mass production of drilling into steel, iron, wood, plastic and various surfaces, it allows a faster RPM and shorter cycle time. The most common types of titanium coatings are Titanium Nitride (TiN), Titanium Aluminum Nitride (TiAN) and Titanium Carbon Nitride (TiCN). TiAN and TiCN are considered superior to TiN as they can increase the lifespan to a considerable degree. The drawback of drill bit coating is that once the tooling becomes blunt, it can’t be sharpened to avoid the coating material being worn away.

4. Cobalt Drill Bit

Cobalt is another type of coating for the drill, cobalt drill bit is used for cutting materials that HSS bit can’t, such as stainless steel and other difficult materials, it can retain hardness at much higher temperatures than HSS and not affected by extremely high heat. But cobalt is a too brittle coating.

5. Carbide-Tipped Drill Bit

Carbide-Tipped drill bit is very hard, easy to dissipate heat and can hold an edge longer than other type bits. Similar to the cobalt drill bit, it’s very brittle as well and maybe broken up in improper use. Carbide bits are applicable for drilling fiberglass reinforced plastic and nonferrous heavy metals.

Reaming shells are used to maintain the diameter of the bore hole and to make sure other drilling equipment does not get stuck down the hole. The outside surface of the reaming shell has natural and synthetic diamonds embedded in a resistant matrix.

Reaming shells come in 6, 10 and 18 inches. How do you know when do you use each size?

6 inch reaming shells

The 6 inch reaming shell is the standard that is used for every kind of rock hardness or ground condition and is the minimum reamer requirement to provide minimum stabilization. Since the 6’’ has only one diamond pad, the vibrations from the rods and outer tube can be conducted easily and make deviation more likely.

When drilling is done in difficult ground conditions, such as swelling clay, a shorter reamer is a good choice as it can get through the ground without catching.

10 inch reaming shells

You need to consider a longer reaming shell once deviation becomes an issue. A 10’ inch reamer is a good compromise between the 6 inch and the 18 inch. The 10 inch has two diamond pads so it will provide better stabilization. A 10 inch reamer is a good choice for underground drilling where adequate space can be a challenge. It will do the job in shallower holes requiring stabilization and where an 18 inch reamer may be just a bit too much.

10’’ is also mainly used with 3m core barrels, so you can still pull your 3m inner tube + extension in one shot.

18 inch reaming shells

You should switch to an extended reaming shell when you have to keep your hole on direction and avoid deviation. The more diamond pads that you have on the reaming shell, the more control you will have on deviation and on hole diameter. The 18 inch gives you 4 pads. The front diamond pads will help you stabilize the core barrel and control the direction while the pads in the back will help maintain the diameter of the hole.

You can use an 18 inch reaming shell on the front end and a diamond type locking coupling on the back to make sure you have good stabilization of the core barrel. You can also use two 18 inch reamers when you have a longer core barrel (6 meters or more). It can act as a core barrel extension allowing you to get more core in the tube at one time.