What is a Core Bit?

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  • Written By: Terrie Brockmann
  • Edited By: Melissa Wiley
  • Last Modified Date: 11 November 2019
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A core bit is a specialized drilling tool. Often an operator uses it to remove an intact core sample from something, such as a rock sample. In other applications, core bits drill large diameter holes such as sink cutouts and passages for wires. Core bits are useful in various commercial and research applications, including geological surveys and oceanic studies. Other types of core bits enlarge pre-drilled or cast holes, but these are solid bits that do not remove intact cores.

One of the uses of a core bit is to collect samples. As it is being cut, the core sample or plug passes through the hollow drill bit into the core barrel. Engineers use core samples to test the strength of construction materials, such as concrete. Scientists use them to study rock formations in search of precious metals or substances, such as oil.

Another use of a core bit is to drill large holes for passages. Often this is useful in construction where wires, conduit, or pipes need to pass through substances such as concrete, masonry, and other construction materials. Typically, electricians use core bits to drill out wooden studs to run electrical and data wiring. Plumbers use different sizes of core bits, from small ones for sink plumbing to large ones for toilet drainage.


The type of core bit that does not collect a core or plug of material is used to enlarge existing holes. Generally, these core bits do not have a tip that will start a hole; therefore, an operator must pre-drill a hole with another type of bit. These core bits are similar to reamers, but reamers shave only a little material from a hole. A core bit may double the size of the hole.

There are different methods for setting up and using core bit drilling systems, depending on the application. Rotary systems use a drilling motion to power the bit. Piston-type systems use a hammering motion that is usually hydraulic-powered.

In order to drill through strong materials such as granite or engineered stone, manufacturers use industrial diamonds and synthetic diamonds for heavy-duty bits. When a worker is using a bit with diamonds, it is necessary to apply light pressure while the bit is working. Allowing the bit to spin freely may cause the diamonds to round off, and the bit segments may heat up and glaze over. This typically ruins bits, which may be rather expensive. Additionally, applying too much pressure may ruin the bit by causing it to crack or warp.

Manufacturers design core bits to use with hand drills, in core bit drill stands, or even mounted on a truck for large, specialty applications. Sometimes the size of the desired core determines the type of tool used. Often mineral core samples may be several feet long. The diameter of the core bit also determines the tool type. While plumbers and electricians use small hand-held drills, core bits that can drill out large diameter cores, such as for manholes, need stronger support.


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