Spotface

Last updated
Spotfacer is marked F. Similar to an endmill but with flat-bottom plunging ability. The tool at E, a counterbore, is also often used for spotfacing in manual machining (not so much in CNC machining). Machined Holes.svg
Spotfacer is marked F. Similar to an endmill but with flat-bottom plunging ability. The tool at E, a counterbore, is also often used for spotfacing in manual machining (not so much in CNC machining).

A spotface or spot face is a machined 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 or forged, 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 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, 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. [1] Other common applications of spotfacing involve facing a pad onto a boss, 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).

Contents

The cutters most often used to cut spotfaces are counterbore cutters and endmills. 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 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 bars 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, [2] with their attendant setup time and part rehandling time. Sometimes the limiting factor in applying this advantage is the difficulty of chip clearance; the operator needs to intervene because chip nests prevent the tool from passing freely and opening and closing freely. [2] 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), [2] 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. [2]

Some fastener designs can obviate spotfacing for some applications. For example, a self-aligning nut 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 exist for the sizes of spotfaces, especially for fastener head seating areas. These standards can vary between corporations and between standards organizations. For example, in Boeing 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 Y14.5-2009 definition of a spotface, which is equal to the flat seat diameter.

See also

Notes

  1. ↑ Degarmo, Black & Kohser 2003 , p. 606.
  2. 1 2 3 4 Hider, Julia, ed. (2018-03-15), "Back-spotfacing tool frees production from costly bottlenecks", Modern Machine Shop , retrieved 2018-03-16.

Related Research Articles

<span class="mw-page-title-main">Shaper</span> Machine tool which linearly cuts or grinds the workpiece

In machining, a shaper is a type of machine tool that uses linear relative motion between the workpiece and a single-point cutting tool to machine a linear toolpath. Its cut is analogous to that of a lathe, except that it is (archetypally) linear instead of helical.

<span class="mw-page-title-main">Metalworking</span> Process of making items from metal

Metalworking is the process of shaping and reshaping metals to create useful objects, parts, assemblies, and large scale structures. As a term it covers a wide and diverse range of processes, skills, and tools for producing objects on every scale: from huge ships, buildings, and bridges down to precise engine parts and delicate jewelry.

<span class="mw-page-title-main">Hobbing</span> Process used to cut teeth into gears

Hobbing is a machining process for gear cutting, cutting splines, and cutting sprockets using a hobbing machine, a specialized milling machine. The teeth or splines of the gear are progressively cut into the material by a series of cuts made by a cutting tool called a hob.

<span class="mw-page-title-main">Machining</span> Material-removal process; manufacturing process

Machining is a process in which a material is cut to a desired final shape and size by a controlled material-removal process. The methods that have this common theme are collectively called subtractive manufacturing, which utilizes machine tools, in contrast to additive manufacturing, which uses controlled addition of material.

<span class="mw-page-title-main">Drill bit</span> Type of cutting tool

Drill bits are cutting tools used in a drill to remove material to create holes, almost always of circular cross-section. Drill bits come in many sizes and shapes and can create different kinds of holes in many different materials. In order to create holes drill bits are usually attached to a drill, which powers them to cut through the workpiece, typically by rotation. The drill will grasp the upper end of a bit called the shank in the chuck.

Broaching is a machining process that uses a toothed tool, called a broach, to remove material. There are two main types of broaching: linear and rotary. In linear broaching, which is the more common process, the broach is run linearly against a surface of the workpiece to produce the cut. Linear broaches are used in a broaching machine, which is also sometimes shortened to broach. In rotary broaching, the broach is rotated and pressed into the workpiece to cut an axisymmetric shape. A rotary broach is used in a lathe or screw machine. In both processes the cut is performed in one pass of the broach, which makes it very efficient.

<span class="mw-page-title-main">Drilling</span> Cutting process that uses a drill bit to cut a circular hole into the workpiece

Drilling is a cutting process where a drill bit is spun to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at rates from hundreds to thousands of revolutions per minute. This forces the cutting edge against the work-piece, cutting off chips (swarf) from the hole as it is drilled.

<span class="mw-page-title-main">Grinding machine</span> Machine tool used for grinding

A grinding machine, often shortened to grinder, is a power tool used for grinding. It is a type of machining using an abrasive wheel as the cutting tool. Each grain of abrasive on the wheel's surface cuts a small chip from the workpiece via shear deformation.

<span class="mw-page-title-main">Countersink</span> To bevel the rim of a hole, so a fastener can be inserted flush with the surface

A countersink 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. 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.

<span class="mw-page-title-main">Counterbore</span> To enlarge the rim of a hole, so a fastener can be inserted flush with the surface

A counterbore 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 screw, is required to sit flush with or below the level of a workpiece's surface.

<span class="mw-page-title-main">Tool and cutter grinder</span>

A Tool and Cutter Grinder is used to sharpen milling cutters and tool bits along with a host of other cutting tools.

<span class="mw-page-title-main">Turning</span> Machining process

Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helix toolpath by moving more or less linearly while the workpiece rotates.

Milling cutters are cutting tools typically used in milling machines or machining centres to perform milling operations. They remove material by their movement within the machine or directly from the cutter's shape.

<span class="mw-page-title-main">Rotary table</span>

A rotary table is a precision work positioning device used in metalworking. It enables the operator to drill or cut work at exact intervals around a fixed axis. Some rotary tables allow the use of index plates for indexing operations, and some can also be fitted with dividing plates that enable regular work positioning at divisions for which indexing plates are not available. A rotary fixture used in this fashion is more appropriately called a dividing head.

<span class="mw-page-title-main">Boring (manufacturing)</span> Process of enlarging an already-drilled hole with a single-point cutting tool

In machining, boring is the process of enlarging a hole that has already been drilled by means of a single-point cutting tool, such as in boring a gun barrel or an engine cylinder. Boring is used to achieve greater accuracy of the diameter of a hole, and can be used to cut a tapered hole. Boring can be viewed as the internal-diameter counterpart to turning, which cuts external diameters.

In the context of machining, a cutting tool or cutter is typically a hardened metal tool that is used to cut, shape, and remove material from a workpiece by means of machining tools as well as abrasive tools by way of shear deformation. The majority of these tools are designed exclusively for metals.

<span class="mw-page-title-main">Hole saw</span> Cylindrical saw used to quickly cut holes

A hole saw, also known as a hole cutter, is a saw blade of annular (ring) shape, whose annular kerf creates a hole in the workpiece without having to cut up the core material. It is used in a drill. Hole saws typically have a pilot drill bit (arbor) at their center to keep the saw teeth from walking. The fact that a hole saw creates the hole without needing to cut up the core often makes it preferable to twist drills or spade drills for relatively large holes (especially those larger than 25 millimetres. The same hole can be made faster and using less power.

Surface finish, also known as surface texture or surface topography, is the nature of a surface as defined by the three characteristics of lay, surface roughness, and waviness. It comprises the small, local deviations of a surface from the perfectly flat ideal.

In manufacturing, threading is the process of creating a screw thread. More screw threads are produced each year than any other machine element. There are many methods of generating threads, including subtractive methods ; deformative or transformative methods ; additive methods ; or combinations thereof.

<span class="mw-page-title-main">Milling (machining)</span> Removal of material from a workpiece using rotating tools

Milling is the process of machining using rotary cutters to remove material by advancing a cutter into a workpiece. This may be done by varying directions on one or several axes, cutter head speed, and pressure. Milling covers a wide variety of different operations and machines, on scales from small individual parts to large, heavy-duty gang milling operations. It is one of the most commonly used processes for machining custom parts to precise tolerances.

References

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.