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.

Left-hand bit

Left-hand bits are almost always twist bits and are predominately used in the repetition engineering industry on screw machines or drilling heads. Left handed drills allow a machining operation to continue when the spindle either cannot be reversed or where the design of the machine makes it more efficent to run left handed. With the increased use of the more versatile CNC machines their usage is less common than when specialised machines were required for machining tasks.

Related Topics:
Repetition - CNC

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They may also be used as an aid in the removal of right-hand screws. Since the rotation of the drill bit is such as it would loosen the screw, using it to drill into the damaged screw head will usually remove the screw, providing the bit "grabs" the damaged material successfully.

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Another type of left-hand bit is an extraction tool used expressly for removing broken or siezed screws, other than by drilling. It has a highly tapered thread structure on it, and is inserted into a drilled hole (of the recommended size) in the damaged screw. If a left hand drill bit is used initially, and the act of drilling the hole does not release the screw, this tool may remove it. In use, the extractor is rotated and the action of the taper and spiral digs into the damaged material causing it to lock tightly and hopefully applies enough pressure to remove the screw. The tool has a tendency to continue winding in while being turned and this may cause the extractor to expand the screw in the hole causing it to bind further, leading to failure of the process or breakage of the extractor. Because of this an alternative extractor has four parallel edges, which tends not to self tighten.

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Image:Left_hand_drill_bit.jpg|An 1/8in left-hand drill bit

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Image:Damaged_screw_removers.jpg|Three sizes of damaged screw removal bits

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Image:ScrewExtractors-square.jpg|square shank, screw extractors

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