How Does a Drill Bit Work?


A drill bit is what actually cuts into the rock when drilling an oil or gas well. Located at the tip of the drillstring, below the drill collar and the drill pipe, the drill bit is a rotating apparatus that usually consists of two or three cones made up of the hardest of materials (usually steel, tungsten carbide, and/or synthetic or natural diamonds) and sharp teeth that cut into the rock and sediment below.


In contrast to percussion drilling, which consists of continuously dropping a heavy weight in the wellbore to chip away at the rock, rotary drilling uses a electric hammer drill bit to grind, cut, scrape and crush the rock at the bottom of the well. The most popular choice for drilling for oil and gas, rotary drilling includes a drill bit, drill collar, drilling fluid, rotating equipment, hoisting apparatus and prime mover.


The prime mover is the power source for the drilling, while the hoisting equipment handles lifting the drill pipe to either insert it into the well or lift it out of the well. Rotating equipment is what sets the whole system in motion. Before the early 1900s, drilling equipment was spun using livestock and a wooden wheel, but now, the rotating equipment is put in motion by a rotary table, which is connected to a square-shaped hollow stem, called a Kelly. Connected to the Kelly is the drill collar, which puts pressure and weight on the drill bit to make it drill through the rock and sediment. Capping off the drillstring is the drill bit, and encompassing the drilling process is drilling fluid, which helps to provide buoyancy to the drill string, lubricate the drilling process and remove cuttings from the wellbore.






Types Of Drill Bits


There are a number of different types of drill bits. Steel Tooth Rotary Bits are the most common types of drill bits, while Insert Bits are steel tooth bit with tungsten carbide inserts. Polycrystalline Diamond Compact Bits use synthetic diamonds attached to the carbide inserts. Forty to 50 times stronger than steel bits, Diamond Bits have industrial diamonds implanted in them to drill extremely hard surfaces. Additionally, hybrids of these types of drill bits exist to tackle specific drilling challenges.


Various drilling designs are also employed for different results, including core bits, which gather formation cores for well logging; mill bits, which help to remove cuttings from the well; and fishtail bits, which enlarge the drill hole above the drill bit.


Different configurations work better on different formations; so a number of different drill bits may be inserted and used on one well. Additionally, drill bits have to be changed due to wear and tear. Drilling engineers choose the drill bits according to the type of formations encountered, whether or not directional drilling is required, for specific temperatures, and if well logging is being done.


When a drill bit, like a masonry drill bit, has to be changed, the drill pipe (typically in 30-feet increments) is hoisted out of the well, until the complete drill string has been removed from the well. Once the drill bit has been changed, the complete drill string is again lowered into the well.


Cutting metal with cutting wheels


Plenty of manual cutting applications call for a hand-held grinder and cutting wheel. Cutting sheet metal, sizing a piece for fabrication, cutting out a weld to refabricate it, and cutting and notching in pipeline work are just a few examples of what can be accomplished using a grinder and cutting wheel.


Resinoid-bonded cutting wheels are a popular choice to achieve these types of cuts because they offer portability and allow you to cut in many different angles and orientations. The bonding agent, in this case resinoid, holds the wheel together so it can cut effectively. The bond wears away as the abrasive grains wear and are expelled so new sharp grains are exposed.


By following a few best practices, you can extend wheel life, promote safety, and improve productivity and efficiency within the process.


The Basics of Cutting Wheels


The main considerations in using resin cutting wheels include the cutting application, the tool being used—such as a right-angle grinder, die grinder, or chop saw—desired cutting action with diamond saw blade, the material being cut, and space. Wheels typically provide a fast cutting action, long life, and tend to be cost-effective.


The two main types of resinoid-bonded abrasive cutting wheels are Type 1, which are flat, and Type 27, which have a raised hub. Type 1 wheels generally are used for straight-on cutting on electric or pneumatic right-angle grinders or die grinders and chop saws, among other tools. Type 27 wheels are required when there is some type of interference and the wheel needs to be raised up from the base of the grinder, but personal preference also plays a role in the decision. They are most commonly used with electric or pneumatic right-angle grinders.


Resinoid-bonded abrasive cutting wheels are available in various sizes and thicknesses. The most popular range is 2 to 16 inches in diameter, and common thicknesses are from 0.045 in. to 1?8 in. Thinner wheels remove less material during the cut.


Some types of wheels cut faster than others. The abrasive material used in the wheel is one influencer on cut rate and consumable life. Wheels come in several grain options, such as aluminum oxide, silicon carbide, zirconia alumina, ceramic alumina, and combinations of these materials.


While not as sharp as other grains, aluminum oxide provides toughness and good performance for cutting on steel. Silicon carbide, on the other hand, is a very sharp grain but not quite as tough, making it suitable for cutting nonferrous metals. Zirconia alumina is a self-sharpening, tough, durable grain that holds up well in a range of demanding applications. Ceramic alumina also is designed to self-sharpen as it “breaks” at predetermined points to maintain a consistent cut rate and long life.


When selecting a resinoid-bonded abrasive wheel, consider that products made with a mixture of zirconia or ceramic alumina with a harder bond typically cost more but offer durability and longer consumable life.


Make sure to refer to the manufacturer’s recommendations, product descriptions, and RPM ratings to select the proper wheel size and bonded abrasive material for your application. Matching the size and RPM rating of the tool to the size and RPM rating of the wheel is critical for safe and effective usage. Choosing the tool with the greatest amperage or amount of torque while staying within size and RPM requirements of the wheel will increase performance.


The kind of tool and the tool guard that you use also are factors that play a role in the type of wheel that can be used for an application. A larger-diameter wheel works best if you’re cutting deep into metal or need to cut a piece with a large diameter, for example, because it eliminates the need to rock the wheel back and forth during the cutting process. Look for a wheel with the diameter designed for the size and thickness of material being cut.


Thin wheels, on the other hand, tend to remove less metal during the cut and have shorter life spans, but provide a quicker cut. There are some exceptions to this as different versions of thin wheels are lasting longer, so be sure to do your research before you make a final decision to ensure the wheel you select maximizes efficiency.


Specialty cutting wheels are also available that are designed for use with certain materials, such as stainless steel and aluminum.


Proper Positioning and Other Tips


In addition to paying attention to designations for RPM rating, size, and material, you should also follow these tips when using resinoid-bonded abrasive cutting wheels.




Use the cutting wheel at a 90-degree angle, perpendicular to the work surface.




Apply the proper amount of pressure—not too much, not too little—to allow the cutting wheel to do the work. Always avoid pushing too hard on the wheel, which can cause the grinder to stall or kick back or give you a much less efficient cutting action. It also increases the chances that you will slip or lose control of the tool, which can cause damage or injury.




Choose a grinder with the highest torque or amperage available for the application, as this will help the wheel to do more of the work. For example, instead of using a 4.5-in. wheel on a 6-amp grinder, use a 4.5-in. wheel on a 10-amp grinder. The RPM rating remains the same, but the tool will provide more torque to cut into the metal.




Choose a tool and consumables that offer quick, consistent cutting, which typically provides the most efficient performance.




Remember, the thinner the cutting wheel, the more susceptible it can be to side loading, which is a term that describes when the wheel bends while moving side to side in the cut. This can turn dangerous if you lean too hard on a wheel, which can cause the wheel to break or jam in the cut. It can also reduce the efficiency of the wheel and increase the cut time.




Store the wheel in a clean, dry environment, and avoid placing it in water or mud. This helps minimize environmental effects that could degrade its performance or cause it to crack or wear prematurely. The performance of resinoid bond tends to deteriorate when the wheel is stored for extended periods of time, so be sure to use FIFO (first in, first out) when using wheels.




Inspect the wheel and consumable before each use to check for signs of damage or wear. Cutting wheels can become harder to control as they wear down. If you can no longer make a safe cut because the wheel’s diameter is worn so thin, then the best course of action is to replace it.




Hole saw basics


Spade bits are the tool of choice for drilling holes up to about 1-1/4 in. in diameter for running electrical wiring and other uses. But when it comes to drilling really big holes for locksets or plumbing pipes, reach for a HSS hole saw. A hole saw is a steel cylinder with saw teeth cut into the top edge. Hole saws don’t cut as quickly as large boring bits driven by a pro’s powerful 1/2-in. drill. But boring bits are expensive ($30 plus drill rental). Hole saws, on the other hand, are readily available at hardware stores and home centers for as little as $5 and work with a standard 3/8-in. drill. Cutting clean holes with hole saws requires a little skill and practice. Here are the key techniques that will make the task safer and give you the best results.


Proper setup is important
Mount the correct-size hole saw in the arbor. If your concrete hole saw has an adjustable center bit, make sure it protrudes past the toothed edge of the saw about 3/8 in. (Photo 2). If the center bit has a flat spot on its shank, align this with the setscrew. Then tighten the setscrew to secure the bit. Finally, tighten the holesaw in the chuck of a corded 3/8-in. variable speed drill. Cordless drills won’t have enough power unless they’re 18 volts or larger.


Start slowly and hold on tight
Photos 1 – 4 show how to drill a hole in a wood door for a lock or door handle, but the same techniques apply for drilling other holes. When you need a clean, splinter-free hole, drill in from both sides (Photos 1 and 4). The key to getting a perfectly straight hole is to ensure even contact at the start. That will put your drill at a right angle to the door (Photo 3).