How To Counter Bore A Hole
A counterbore in a metal plate
A counterbore (symbol: ⌴) is a cylindrical apartment-bottomed hole that enlarges another coaxial hole, or the tool used to create that feature. A counterbore hole is typically used when a fastener, such as a socket caput cap spiral or fillister head screw, is required to sit affluent with or below the level of a workpiece's surface.
Whereas a counterbore is a apartment-bottomed enlargement of a smaller coaxial pigsty, a countersink is a conical enlargement of such. A spotface often takes the grade of a very shallow counterbore.
As mentioned above, the cutters that produce counterbores are oft also called counterbores; sometimes, to avoid ambiguity, the term counterbore cutter is used instead.
The symbol is Unicode character U+2334 ⌴ COUNTERBORE.
Description [edit]
Comparison of countersunk and counterbored holes.
Counterbore cutter marked 'Eastward
A counterbore hole is usually used when the caput of a fastener, such as a hex head or socket head capscrew, is required to be flush with or below the level of a workpiece's surface.
For a spotface, fabric is removed from a surface to make it flat and smooth, usually for a fastener or a bearing. Spotfacing is ordinarily required on workpieces that are forged or cast. A tool referred to as a counterbore is typically used to cutting the spotface, although an endmill may likewise be used. Merely enough material is removed to make the surface flat.[1]
A counterbore is also used to create a perpendicular surface for a fastener head on a non-perpendicular surface. If this is not feasible and so a cocky-aligning nut may be required.
By comparison, a countersink makes a conical hole and is used to seat a flathead screw.
Standards exist for the sizes of counterbores, especially for fastener head seating areas. These standards tin vary between corporations and between standards organizations. For case, in Boeing Pattern Manual BDM-1327 section iii.5, the nominal bore of the spotfaced surface is the aforementioned equally the nominal size of the cutter, and is equal to the flat seat bore plus twice the fillet radius. This is in dissimilarity to the ASME Y14.5-2009 definition of a spotface, which is equal to the apartment seat diameter.
Machining [edit]
2 types of counterbore tools
Counterbores are made with standard dimensions for a certain size of spiral or are produced in sizes that are not related to any particular screw size. In either case, the tip of the counterbore has a reduced bore section referred to as the pilot, a feature essential to assuring concentricity between the counterbore and the hole being counterbored. Counterbores matched to specific screw sizes generally have integral pilots that fit the clearance hole bore associated with a particular screw size (e.yard., .191 inches for a number 10 machine screw). Counterbores that are not related to a specific spiral size are designed to take a removable pilot, assuasive any given counterbore size to be adapted to a variety of pigsty sizes. The pilot matters piddling when running the cutter in a milling setup where rigidity is assured and pigsty center location is already achieved via X-Y positioning.
The uppermost counterbore tools shown in the prototype are the same device. The smaller top detail is an insert, the eye shows another three-fluted counterbore insert, assembled in the holder. The shank of this holder is a Morse taper, although there are other machine tapers that are used in the industry. The lower counterbore is designed to fit into a drill chuck, and beingness smaller, is economical to brand as one piece.
See too [edit]
- Countersink
Notes [edit]
- ^ Degarmo, Black & Kohser 2003, p. 606.
References [edit]
- Degarmo, E. Paul; Blackness, J T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, ISBN0-471-65653-4 .
Source: https://en.wikipedia.org/wiki/Counterbore
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