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Twist Drill Bits
Twist drills are one of the most common types of drill bits and usually used to cut through metal. They often have two cutting edges and two flutes to remove chips as the hole is cut. Several factors should be considered when selecting a twist drill bit as the drill's material, point, length and coating all determine whether it is suitable for a light-duty general purpose project or a heavy-duty, challenging application. AFT is pleased to offer twist drills in all shapes and sizes from HTC, Milwaukee and Norseman Drill & Tool. With so many options, you're sure to find the right tool for the job.
Selecting a Twist Drill Bit
Point Style
A conventional 118-degree point is the most common and useful for general purpose applications. The more heavy-duty 135-degree split point offers speed and accuracy because it penetrates quickly at the drill site without "walking" and without the need for a center punch.
Length
Twist drills are classified into five standard length groupings. Jobber drills fall into the middle of the spectrum and are considered the standard length within the industry. Because of this, they are the most common drill bit size and have a wider selection available. Moving up the length spectrum, you'll find taper length and then extra length drills. These drills offer longer overall length for applications that require extra reach or an extra deep hole. On the descending side of the spectrum, Mechanics length drill bits are shorter than jobber drills and screw machine length drill bits are the shortest. Shorter drill lengths offer added rigidity and sturdiness. It should be noted that a drill's diameter is directly correlated to its length. Meaning that the thicker the diameter, the longer the drill will be in that group and vice versa, unless the group has a fixed length, such as Silver & Deming drills.
Material
The material that a drill bit is manufactured from dictates the speed and toughness of the drill as well as what applications a drill is suited for.
High Speed Steel is a non-carbon alloy steel that offers high hardness, heat and abrasion resistance that equates to faster drilling speeds than carbon alloy steel. It is recommended for general purpose drilling in carbon steel, ferrous and nonferrous metals.
Cobalt steel is a high speed steel alloy with added carbon that results in higher red hot hardness and therefore faster speeds in comparison with standard HSS bits. It is suitable for drilling stainless steel, hardwoods, titanium alloys and other hard metals or high tensile strength materials.
Carbide steel offers extreme hardness that can drill most materials while keeping its edge. It is more brittle than steel, however. It is ideal for difficult or abrasive materials such as cast iron, fiberglass and nonferrous metals.
Coatings
The most common and economical coating is Black Oxide which offers heat resistance, lubricity and corrosion resistance while extending tool life.
Titanium Nitride (TiN) is a hard ceramic coating material that extends tool life by three times and offers lubricity that increases speed.
Titanium Aluminum Nitride (TiAin) is similar but superior to TiN coatings and extends tool life up to five times.
A bright finish means that no surface coating is applied. Rather, flutes are precision polished for improved chip removal and suitable for drilling nonferrous metals, wood and plastics.
