Types of Countersinks
– Normal countersunk angles: 60°, 82°, 90°, 100°, 110°, 120°
– Types of thread: American inch screws (UNC, UNF, UNS), ISO metric, British imperial inch screws (BA, BSF, BSW, etc.), Unified National (i.e. inch size) Aviation fasteners
Machining Countersinks
– Countersinks can be used in drills, drill presses, milling machines, and lathes
– Cross-hole countersink cutter: cone-shaped tool with a cutting edge provided by a hole that goes through the side of the cone
– Fluted countersink cutter: used to provide a heavy chamfer in the entrance to a drilled hole
– Back countersink: two-piece countersink used on tough-to-reach areas
– Speeds, feeds, and avoiding chatter: shorter and more rigid setups reduce chatter, better-quality fluted countersink cutters have irregular pitching to reduce undulated surfaces
Form Countersinking
– Form countersinking, also known as dimpling, is a countersink formed into sheet metal to increase the strength of a structure
– Coin dimpling and modified radius dimpling are two processes for producing formed countersinks
– Dimples in thick sheet metal can be tapped to yield a threaded hardpoint on the sheet
Related Concepts
– Counterbore: creates a flat-bottomed hole
– Speeds and feeds: factors to consider when using countersinks
– Spotface: creates a smooth, flat surface around a hole
References and Bibliography
– Warrendale, PA (2013). Automated/mechanized drilling and countersink of airframes. ISBN 978-0-7680-7646-2.
– MIL-STD-1515A, MILITARY STANDARD: FASTENER SYSTEMS FOR AEROSPACE APPLICATIONS
– Reithmaier 1999, p.90
– Reithmaier 1999, p.91
– Reithmaier, Lawrence W. (1999), Standard aircraft handbook for mechanics and technicians (6th ed.), McGraw-Hill Professional, ISBN 978-0-07-134836-2. Source: https://en.wikipedia.org/wiki/Countersink
This article needs additional citations for verification. (November 2009) |
In manufacturing, a countersink (symbol: ⌵) is a conical hole cut into a manufactured object, or the cutter used to cut such a hole. A common use is to allow the head of a countersunk bolt, screw or rivet, when placed in the hole, to sit flush with or below the surface of the surrounding material (by comparison, a counterbore makes a flat-bottomed hole that might be used with a socket-head capscrew). A countersink may also be used to remove the burr left from a drilling or tapping operation, thereby improving the finish of the product and removing any hazardous sharp edges.
The basic geometry of a countersink (cutter) inherently can be applied to the plunging applications described above (axial feed only) and also to other milling applications (sideways traversal). Therefore, countersinks overlap in form, function, and sometimes name with chamfering endmills (endmills with angled tips). Regardless of the name given to the cutter, the surface being generated may be a conical chamfer (plunging applications) or a beveled corner for the intersection of two planes (traversing applications).
