the.com/countersink
the cone-shaped grave dug so a screw head can lie flush and dignified.
means To bore a cone-shaped recess at the mouth of a hole so that a screw or bolt head sits flush with or below the surface — or the tool that does it.
from A transparent compound of "counter-" (against, opposite, in response to) and "sink" (to make something go down or below a level). The "counter-" comes via French from Latin "contra," while "sink" descends from Old English "sincan," to subside or settle downward. The word does exactly what it says: you sink a recess to receive what would otherwise stand proud, the carpentry sense settling into place by the 18th–19th century as fastener-heads multiplied.
- the angle
- Most are 82 or 90 degrees by standard
- vs counterbore
- Counterbore is flat-bottomed; countersink is conical
- chatter problem
- Odd flute counts reduce vibration marks in metal
- naval roots
- Flush rivets cut drag on aircraft and ships
- double duty
- Also deburrs holes after drilling
countersink drill bit — tapered cutting tool used to create conical recesses in wood, metal, or plastic for flush screw installation
countersink angle — typically 82° or 90° cone angle standard in iso 14587 for screw head accommodation