Drill bit

Drill bits are the cutters of drill tools. Bits are interchangeable, meaning that they can be removed from the end of the drill, either to replace a worn part or to change the size of the part.

Core drill

A core drill bit (as pictured) is used to enlarge an existing hole. The existing hole may be the result of a core from a casting or a stamped (punched) hole.

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The name of this bit may be somewhat confusing.

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• A diamond core drill bit cuts a cylindrical core, cutting an annulus in the workpiece. The diamond core bit is cylindrical.
• A core drill bit is named because its first use was in drilling out the hole left by a foundry core, a cylinder placed in a mould for a casting that leaves an irregular hole in the product. This core drill bit is solid.

Core drill bits are similar in appearance to reamers as they have no cutting point or means of starting a hole. They have 3 or 4 flutes which enhances the finish of the hole and ensures the bit cuts evenly. Core drill bits differ from reamers in the amount of material they are intended to remove. A reamer is only intended to enlarge a hole a slight amount which, depending on the reamers size, may be anything from 0.1 millimeter to perhaps a millimeter. A core drill bit may be used to double the size of a hole.

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Using an ordinary two-flute twist drill to enlarge the hole resulting from a casting core will not produce a clean result, the result will possibly be out of round, off center and generally of poor finish. The two fluted drill also has a tendency to grab on any protuberance (such as casting flash) which may occur in the product.

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