Carbide Drills (Bits and Tips) – An Introduction


Carbide drills are among the best types of drills one can get in terms of durability and cutting ability. The tungsten carbide drill is the most common, and is generally just referred to as a carbide drill. There are however other types aside from tungsten. These drills are made of material that is very hard and strong, and so are able to drill into just about any kind of material, even high density ones like stainless steel. They are however fairly expensive compared to their steel counterparts. Carbide drills also have other advantages, which we will look into.

Drills and Drill Bits Terminology

First it would be beneficial to review some of the terminology pertaining to drills, before we look more in depth at carbide drills. The term drill can refer to the drilling machine itself that has the motor to spin the bit that bores the holes. It can also refer to the drill bit, which as just mentioned, is what is used to interface with the surface and do the actual boring or cutting. The other side of the drill bit is called the shank. For the purposes of this article, the terms drill and drill bit will be used synonymously unless clearly indicated otherwise.

Drill Wear and Tear – Carbide Drills last longer

Each time a drill is used to bore an object, there is some deterioration to the bit itself. The friction between the bit and the surface on which it is impacting, causes heat to be generated, which wears down the bit causing it to become dull over time. Eventually it will need regrinding (which can only be done a limited number of times) and replacing altogether. It is also known that the structural integrity of the drill bit can also get compromised with the continual heating and cooling experienced in the bit. Carbide drill bits generally last longer and stay sharper than other bit kinds. For example, they can last up to 25 times longer than the average steel bits.

Drilling Tolerance -carbide drills have lowest tolerances

One of the major factors that determine the type of drill needed for a particular job is the tolerance associated with the particular drill. Tolerance basically gives an idea of how close the drill will come to producing the required hole size. It is the difference between the diameter of the drill bit being used, and the diameter of the largest hole one could expect from using this drill bit. The smaller the hole, the smaller the tolerance. Carbide drill bits have the lowest tolerances, which means they tend to be more accurate than other drills.

Carbide Drill Bit Types

When one refers to a carbide drill, it is possible that one is referring to a carbide coated drill, a solid caribide drill bit, a brazed drill with a carbide tip, or an exchangeable drill bit tip that uses a carbide crown. It is important to understand what is meant by each, as this will impact the choice of drill to use for a particular job.

Carbide Coated Drills

These drills are technically not carbide drills. They are usually steel or high speed steel coated with carbide. This increases the life span of the drill by approximately 2 to 3 times and can be used to drill thin metals.

Solid Carbide Drills

These drill bits are wholly carbide. It is not just coated steel, or an adjoining of steel and carbide. Solid carbide drill bits tend to be brittle and so are at risk of breaking if usage requires some flexibility of the bit, such as on lathes. On the plus side, this stiffness allows them to have the lowest tolerance measures among carbide drills, making them the most accurate. Note though, they happen to also be the most expensive.

Brazed Carbide Tipped Drills

A brazed tipped drill is essentially a drill bit that has another metal type welded to the end by means of a filler metal or alloy. A brazed carbide drill is usually a steel bit drill with a carbide tip brazed on. This is cheaper than a solid carbide drill and is still fairly accurate. The tolerance is just about twice that of the solid carbide drills for comparable drill diameters. The steel body of this drill allows enough flexibility that the solid carbide does not, and so can work on lathes. Brazed drills have a self-centering geometry, as they have two symmetrical edges for cutting. This is a very stable design that makes it possible for the drill to bore materials at top feedrates, except where the entrance might be angled, in which case, the feed should be reduced by up to 50% both when entering and exiting.

Exchangeable Carbide Drill Bit Tip

There are drills available that allows the tip to be replaced as needed. This type of drill is similar to the brazed in that the head or tip (also called the crown) of the drill can be of a different metal than the main drill body, such as a carbide crown. However, the tip is not brazed on, but can be replaced. Various size crowns are available, so with just one drill, it is possible to drill varying size holes. Replacing a crown costs almost the same as regrinding a brazed or solid drill. As mentioned earlier, regrinding can only be done a very limited number of times. But with a drill where the crown can be replaced, the drill bit will last much longer, as there is no need to do any regrinding. This makes this type of drill very economical. Regrinding diminishes the precision and overall performance of the drill, as it is very difficult to replicate the precise shape and other relevant details in the regrinding process. The exchangeable crown drill does not have this problem, as the crown is simply replaced when necessary. Another benefit of this kind of drill is that, like the brazed drill, it has self-centering geometry and can enter materials at full feedrates.

Having looked at the different types of carbide drills, and seeing their advantages and disadvantages with respect to each other, as well as their benefits over other types of drills (like steel or high speed steel), one can see that it makes sense to get a carbide drill if one can afford it. They are more accurate, they last longer, and they are able to bore into very hard materials. If one intends to cut metal, then a carbide drill might be the most effective option, and when it comes to high density materials like stainless steel, it might be the only option.

You can learn more about carbide drills at this site.

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