Lathe Drilling, Countersinking, and Reaming - 7: Chamfering/Countersinking
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
The terms "countersink" and "chamfer" are sometimes used interchangeably.

Countersinking is usually used to provide a nest for the top a flat head screw.

Chamfers are used after a hole has been drilled and a small chamfer is desired on the edge of the hole. Chamfers are a must when the hole is going to be tapped or reamed. The chamfer provides a start for the next tool, as well as eliminates tool impact shock to the reamer or tap.

Although it is not important for engineering purposes, it should be noted that 99% of the countersinking done is for flat head screws so that their heads will fit below the surface of the part. Most flat head screws are either 80°, 82°, or 100°. Therefore some machinists call these cutter angles countersinking tools and all other angles chamfering tools. R.S.
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label: lathe drilling, countersinging, reaming, tailstock alignment, indicating, center drilling, chamfering