A spotface or spot face is a

machined Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...

feature in which a certain region of the workpiece (a spot) is faced, providing a smooth, flat, accurately located surface. This is especially relevant on workpieces

cast Cast may refer to: Music * Cast (band), an English alternative rock band * Cast (Mexican band), a progressive Mexican rock band * The Cast, a Scottish musical duo: Mairi Campbell and Dave Francis * ''Cast'', a 2012 album by Trespassers William * ...

forged Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which it ...

, where the spotface's smooth, flat, accurately located surface stands in distinction to the surrounding surface whose roughness, flatness, and location are subject to wider

tolerances Engineering tolerance is the permissible limit or limits of variation in: # a physical dimension; # a measured value or physical property of a material, manufacturing, manufactured object, system, or service; # other measured values (such as t ...

and thus not assured with a machining level of precision. The most common application of spotfacing (spot facing) is facing the area around a bolt hole where the bolt's head will sit, which is often done by cutting a shallow

counterbore A counterbore (symbol: ⌴) is a cylindrical flat-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 head cap screw or fillister head ...

, just deep enough "to clean up"—that is, only enough material is removed to get down past any irregularity and thus make the surface flat.. Other common applications of spotfacing involve facing a pad onto a

boss Boss may refer to: Occupations * Supervisor, often referred to as boss * Air boss, more formally, air officer, the person in charge of aircraft operations on an aircraft carrier * Crime boss, the head of a criminal organization * Fire boss, a ...

, creating planar surfaces in known locations that can orient a casting or forging into position in the assembly; allow part marking such as stamping or nameplate riveting; or offer machine-finish visual appeal in spots, without the need for finishing all over (FAO). The cutters most often used to cut spotfaces are

cutters and

endmill An end mill is a type of milling cutter, a cutting tool used in industrial milling applications. It is distinguished from the drill bit in its application, geometry, and manufacture. While a drill bit can only cut in the axial direction, most m ...

s. In manual machining especially, the former is useful because its pilot guides the cutter into the correct location (established by the bolt hole), and its cutting lips are perpendicular to the hole axis with no relief angle, meaning that a plunging cut, moving in only the Z-axis, will leave a flat surface. In contrast, most general-purpose endmills have a relief angle such that a plunging cut (Z-axis-only toolpath) will leave a very slightly convex surface. But in

CNC Numerical control (also computer numerical control, and commonly called CNC) is the automated control of machining tools (such as drills, lathes, mills, grinders, routers and 3D printers) by means of a computer. A CNC machine processes a ...

machining this is irrelevant, because the flat spotface is left by circular interpolation of the endmill as it traces a circular toolpath in the XY plane. Zero-angle cutters obviate this, functioning similarly to the traditional counterbore cutters of manual machining but needing no pilot. Spot facing of larger planar surfaces sometimes employs face mills. Backspotfacing (back spot facing) is analogous to backboring, meaning that the tool manages to reach to the far side of the workpiece (away from the spindle side) and cut back toward the spindle. Such operations can be done with

boring bar A boring bar is a tool used in metalworking and woodworking. Boring is a technique used in many aspects of building. Woodworkers have used boring as a form of drilling for centuries. In woodworking, the boring tool is static in size and used to ...

s reaching through a hole while shifted off-center, then shifting onto center for the cut (for example, in the G76 fine boring cycle), or with back-deburring style tools whose cutting edges open and close in umbrella-like or check-valve-like fashion. Such back-cutting operations can obviate second operations, with their attendant setup time and part rehandling time. Sometimes the limiting factor in applying this advantage is the difficulty of

chip Chromatin immunoprecipitation (ChIP) is a type of immunoprecipitation experimental technique used to investigate the interaction between proteins and DNA in the cell. It aims to determine whether specific proteins are associated with specific genomi ...

clearance; the operator needs to intervene because chip nests prevent the tool from passing freely and opening and closing freely. In such cases, improved chipbreaking via different inserts in the main operation may help, and backspotfacing tools powered by coolant pressure and using through-tool coolant feed may succeed where others cannot (opening, cutting, and retracting despite some chips), not only obviating a second operation but also making the main operation less reliant on operator intervention and program stops ( M00 or M01) than a lesser backspotfacing tool would. Some fastener designs can obviate spotfacing for some applications. For example, a

self-aligning nut A flange nut is a nut that has a wide flange at one end that acts as an integrated washer. This serves to distribute the pressure of the nut over the part being secured, reducing the chance of damage to the part and making it less likely to loosen ...

allows the nut to find its own perpendicularity to the thread axis by floating via a pair of spherical bearing surfaces (a ball-in-cup arrangement).

Standards Standard may refer to: Symbols * Colours, standards and guidons, kinds of military signs * Standard (emblem), a type of a large symbol or emblem used for identification Norms, conventions or requirements * Standard (metrology), an object th ...

exist for the sizes of spotfaces, especially for fastener head seating areas. These standards can vary between corporations and between

standards organization A standards organization, standards body, standards developing organization (SDO), or standards setting organization (SSO) is an organization whose primary function is developing, coordinating, promulgating, revising, amending, reissuing, interpr ...

s. For example, in

Boeing The Boeing Company () is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, telecommunications equipment, and missiles worldwide. The company also provides leasing and product ...

Design Manual BDM-1327 section 3.5, the nominal diameter of the spot-faced surface is the same as the nominal size of the cutter, and is equal to the flat seat diameter plus twice the fillet radius. This is in contrast to the

ASME The American Society of Mechanical Engineers (ASME) is an American professional association that, in its own words, "promotes the art, science, and practice of multidisciplinary engineering and allied sciences around the globe" via "continuing ...

Y14.5-2009 definition of a spotface, which is equal to the flat seat diameter.

Notes

References

*{{Citation , last = Degarmo , first = E. Paul , last2 = Black , first2 = J T. , last3 = Kohser , first3 = Ronald A. , title = Materials and Processes in Manufacturing , publisher = Wiley , year = 2003 , edition = 9th , isbn = 0-471-65653-4. Machining Metalworking terminology

See also

Notes

References