11/25/19 - Zoro Staff
The answer to the question of how to select the right drill bit begins with the material you will be drilling. Another key consideration is the purpose of the hole you need to create. The following information will assist you in buying and using the right bit and could prevent:
- project delays
- ineffective processes
- broken tools or work pieces, and
- unsafe practices
No matter how standard or customized your drill, the success of your project will depend on whether you’ve chosen the proper drill bit for the material you will be drilling (the material is often referred to as the “substrate”), as well as the proper bit diameter for the hole you need to create.
Factors that influence the success of drilling a given substrate include:
- the type of metal the bit is made of
- the bit point tip
- the length of the bit, and
- how or whether the bit is coated
Choose a Drill Bit Made of the Right Material
The right drill bit material, or metal, is always determined by the factor of hardness. Choose a bit made of harder metal for harder substrates such as sheet metal, steel, masonry or even rock.
Choose a bit made of material that is harder than the substrate.
|Drill Bit Material||Application (substrate)|
|High Speed Steel (HSS)||For general purpose (wood or drywall), carbon steel, ferrous and nonferrous metals|
|Cobalt||For stainless steel, armor plating, and other hard metals|
For difficult or abrasive materials like cast iron, fiberglass, and nonferrous metals
Choose the Right Drill Bit Point Type
The point type used for most general-purpose applications is called the “conventional point”. Among conventional point drill bits, the 118° drill point angle is most common for drywall, wood and generally softer substrates. The next most common point is the 135° split point. This point is commonly used in heavy-duty applications. It is ideal for tight tolerance situations, and the increased angle bites into the substrate, preventing the bit from straying or “walking” across the substrate and possibly damaging it, or causing injury to the drill operator.
Choose the Right Length for Your Drill Bit
Drill bits come in 5 standard length groups:
- Jobber Length Drill Bits - these are the most common bits, used for general purposes and having flute lengths between 9 and 14 times the diameter of the drill.
- Taper Length Drill Bits - these are engineered for the purpose of pre-drilling pilot holes for the shanks of wood screws.
- Extra Length Drill Bits - also known as “aircraft-length” drill bits, a name carried over from their original purpose of drilling through an airplane fuselage.
- Mechanics Length Drill Bits - these bits have a shorter flute length and a shorter overall length than a standard jobber bit, making them less prone to breakage and suitable for harder drilling.
- Screw Machine Length Drill Bits - these are the shortest of the bits, having the lowest length-to-diameter ratio.
Note that bit diameter will determine overall length. For example, a ⅛” jobber bit will be shorter than a ¼” jobber bit.
Choose the Right Coating for Your Drill Bit
Some drill bit manufacturers provide a coating on their bits to extend bit life and enable performance advantages under certain conditions. The four most common coatings are:
- Black Oxide Coating - the most common coating, black oxide helps retain lubricants used for smoother, cooler drilling. It is not recommended for non-ferrous metals like aluminum.
- TiN Coating - a titanium nitride coating provides extra lubricity at the drill point, for higher drilling speeds and longer tool life.
- TiAIN Coating - titanium aluminum nitride coatings are most effective when higher drill speeds and feed rates are required. Works well on stainless steel, titanium, ferrous metals, and high-temperature alloys.
- Bright Finish - this term means the bit has no surface coating. The flutes are polished for improved chip removal. This option works well for nonferrous metals such as aluminum.
When working with drills, ensure your safety with protective eyewear.
Product Compliance and Suitability
The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.