US20130225050A1

US20130225050A1 - Localized spot lapping on a larger work surface area

Info

Publication number: US20130225050A1
Application number: US13/612,791
Authority: US
Inventors: Collin Chan; Brian Miehm; Simon Lancaster-Larocque; Ryan M. SATCHER
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2012-02-24
Filing date: 2012-09-12
Publication date: 2013-08-29

Abstract

An apparatus for lapping a portion of an exterior surface of a housing is described. The apparatus includes at least a lapping tool arranged to execute a lapping operation. The lapping tool takes the form of a lapping pad which includes a conduit through which slurry can be transported for local deposition on the housing during a lapping operation. The apparatus also includes a stage on which a workpiece in the form of a housing is mounted. During the lapping operation, slurry is passed through the slurry conduit in the lapping tool, the lapping tool and the housing are moved in various motions. In this way, a gradual transition region is created between an accessory region and the remainder of the housing.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application Ser. No. 61/603,177, filed Feb. 24, 2012, entitled LOCALIZED SPOT LAPPING ON A LARGER WORK SURFACE AREA, the entire disclosure of which is hereby incorporated by reference in its entirety and for all purposes.

BACKGROUND

1. Technical Field
The present invention relates generally to the polishing of a three dimensional metal alloy object. More particularly, a method and an apparatus are described for polishing a portion of an exterior surface of a housing of a portable electronic device to form a visually continuous flat top edge surface.
2. Related Art
The proliferation of high volume manufactured, portable electronic devices has encouraged innovation in both functional and aesthetic design practices for enclosures that encase such devices. Manufactured devices can include a housing that provides an ergonomic shape and aesthetically pleasing visual appearance desirable to the user of the device. Exterior surfaces of housings of portable electronic devices can be shaped by computer numerically controlled machinery and can include combinations of flat regions and curved regions as well as accessory regions such as logos and the like. Irregularities in the surface of the surface between the accessory region and the remainder of the housing can result in an unacceptable appearance due to visual artifacts caused by physical transitions between the two regions. For example, if the accessory region and the remainder portion of the housing are separated by an abrupt change in surface finish, then this change can be visible rendering an unappealing transition between the accessory region and the rest of the housing.
Thus there exists a need for a method and an apparatus for polishing a surface of a housing resulting in a surface with a consistent surface variation within a tolerance required to achieve a desired surface appearance upon finishing.

SUMMARY

The embodiments relate to a system, method and apparatus for creating a gradual transition region between a polished accessory region and the remainder of a surface portion of a metal housing.
In one embodiment, an apparatus for creating a gradual transition region between an accessory region and a surrounding exterior surface region of a housing is disclosed. The apparatus includes a lapping tool. The lapping tool includes a lapping pad. The lapping pad includes at least the following: (1) a centerpoint surrounded by a central portion, and (2) a peripheral portion. During a lapping operation the centerpoint of the lapping pad is compelled to follow a lapping path, the lapping path includes a number of lapping segments. Each lapping segment substantially crosses the accessory region at an angle different than a preceding lapping segment and each lapping segment puts a peripheral portion of the lapping pad in tangential contact with a central area of the accessory region, thereby creating the gradual transition region.
In another embodiment a manufacturing method is disclosed. The manufacturing method includes at least the following steps: (1) mounting a housing to a stage, where the housing includes at least a first region, a second region surrounded and defined by the first region, and a transition region disposed between the first region and the second region; (2) positioning a lapping tool in physical contact with a portion of the second region during a lapping operation, the lapping tool including a lapping pad having a central portion and a peripheral portion; and (3) finishing the transition region by causing the lapping pad to follow a lapping path, the lapping path comprising a number of lapping segments, each lapping segment substantially crossing the second region at an angle different than a preceding lapping segment and each lapping segment putting the peripheral portion of the lapping pad in tangential contact with a central area of the second region.
In yet another embodiment a lapping assembly is disclosed. The lapping assembly includes at least the following: (1) a lapping tool comprising a rotating lapping plate coupled to a lapping pad; (2) a force sensor coupled to the lapping tool for regulating pressure exerted by the lapping tool; and (3) a stage configured to maneuver a housing in a plane substantially parallel with the lapping pad during a lapping operation, the housing having an exterior surface with an accessory region and a surrounding surface region. During a lapping operation the lapping pad is compelled to follow a lapping path, the lapping path includes a number of lapping segments, each lapping segment substantially crossing the accessory region at an angle different than a preceding lapping segment and each lapping segment putting a peripheral portion of the lapping pad in tangential contact with a central area of the accessory region, thereby creating a gradual transition region between the accessory region and the surrounding surface region.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which:

FIG. 1A-1B illustrate a housing with an accessory region;

FIGS. 1C-1E illustrate cross-sectional view of accessory regions;

FIG. 2 illustrates one embodiment of a lapping machine assembly;

FIG. 3 illustrates a perspective view of one embodiment of a lapping tool;

FIG. 4A illustrates a cross-sectional view of a lapping tool;

FIG. 4B illustrates a lapping tool configured to deliver slurry to a number of slurry conduit branches distributed across the surface of a lapping plate;

FIG. 4C illustrates a lapping tool configured with a variable flexibility lapping plate;

FIG. 4D illustrates a lapping tool with an externally arranged slurry delivery conduit;

FIG. 5 illustrates a top view of one possible center weighted pattern that can be employed during a lapping operation;

FIG. 6 illustrates alternative center weighted paths that can be used with previously described embodiments; and

FIG. 7 illustrates a flow chart detailing a representative lapping process in accordance with the other previously described embodiments.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The present invention relates generally to the polishing of a three dimensional metal alloy object. More particularly, a method and an apparatus are described for polishing an exterior surface of a metal alloy housing of a portable electronic device to form a combination of a flat top edge surface, a curved edge surface and a flat bottom surface.
In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the present invention.
High volume manufactured portable electronics devices can include computer numerically controlled (CNC) machined metal alloy parts with various geometrically shaped surfaces. Representative portable electronic devices can include portable media players, portable communication devices, and portable computing devices, such as an iPod®, iPhone° and iPad® manufactured by Apple, Inc. of Cupertino, Calif. Both the tactile and visual appearance of a portable electronics device can enhance the desirability of the portable electronic device to the consumer. Housings can be used that include metal alloys which can provide a lightweight material that exhibits desirable properties, such as strength and heat conduction well suited for housings of portable electronic devices. A representative metal alloy can include an aluminum alloy. Both the tactile and visual appearance of a portable electronics device can enhance the desirability of the device to the consumer. A cosmetic outer layer machined from a metal alloy can be cut to a desired shape and polished to a desired reflective and/or matte appearance. In some embodiments, a continuously smooth shape having a uniformly visually smooth appearance is desired.
High volume manufacturing can benefit greatly from minimized processing time. Machining an aluminum billet to form the exterior surface of a housing of a portable electronic device using a single cutting tool can reduce the processing time required. Machining with a single continuous optimized path can result in a “rough” cut surface that can require minimal sanding and polishing to produce a visually smooth finish with no visually discernible breaks between regions having different cross sections. Curved regions can transition smoothly into flat regions including along corner areas without any visual change in surface appearance. In some cases specific regions along an exterior surface of the housing require additional polishing operations to achieve a desired polishing effect across that surface. Since polishing operations generally result in material removal, polishing operations targeting a discrete area for a smoother or shinier finish can cause a surface variation in the previously continuous surface of the housing. Unfortunately, in some cases the variation can cause an abrupt change between surface areas that can mar the overall look and feel of the housing.
In one embodiment a lapping process can be utilized to create a gradual transition region between the aforementioned accessory region and the less thoroughly polished remainder of the housing. The process can be referred to as spot lapping as the lapping operation is focused on a particular portion of the housing. A lapping tool associated with the lapping process is aligned parallel with the surface of the housing and maneuvered with respect to the surface of the housing during the lapping operation by a stage. The stage permits maneuvering of the housing in a number of degrees of freedom allowing movement in at least an X-Y plane. The lapping tool can be a rotary polishing tool configured to spin an abrasive pad across the surface of the housing. By maneuvering the lapping tool along a lapping path with respect to the housing such that efficient material removal portions of the lapping tool spends more time over a central portion of the depression than over peripheral portions of the depression a gradual transition region can be established, thereby smoothing an abrupt visual or tactile change between the accessory region and the remainder of the surface of the housing.
Various embodiments of lapping methods suitable for establishing a smooth transition region across a portion of a surface of a metal substrate are discussed below with reference to FIGS. 1A-7. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes as the full extent of the embodiments goes beyond these limited descriptions.
FIG. 1A illustrates a housing with an accessory region. For exemplary purposes the housing will be referred to as an aluminum housing, but it should be noted that the embodiments described within this application can be applied to any substrate well suited to lapping operations. Aluminum housing 100 includes accessory region 102. Accessory region 102 in this embodiment is a finely polished or in some embodiments mirror polished region of aluminum housing 100. Consequently, aluminum housing 100 includes abrupt transition region 104 between accessory region 102 and surrounding surface region 106. Abrupt transition region 104 can arise from additional polishing operations targeted only at accessory region 102 of aluminum housing 100 for achieving the highly polished surface finish associated with accessory region 102. In one embodiment accessory region 102 can have a mirror polished finish while surrounding surface area 106 can have a matte, bead blasted, anodized consistency. Abrupt transition region 104 can mar the overall look and feel of the device. Depending on the size and abruptness of abrupt transition region 104, this region can cause a significant tactile disruption across an otherwise smooth and continuous surface of aluminum housing 100. Instead of experiencing a continuously smooth surface an abrupt change in surface consistency is encountered by anyone moving a finger between accessory region 102 and the more coarsely textured surrounding surface region 106. FIG. 1B illustrates a housing 100 after undergoing a lapping operation. Abrupt transition region 104 is replaced by gradual transition region 108, which expanding radially outward from accessory region 102. In this way a gentle tactile transition from a smooth to a more coarse texture can be established, thereby resulting in a more appealing look and feel to aluminum housing 100.
FIG. 1C illustrates a cross sectional view of aluminum housing 100 as defined in FIG. 1A along cross section A-A. In this depiction abrupt transition region 104 is embodied as a rapid change in texture between accessory region 102 and surrounding surface region 106. Surface region 106 includes multiple scalloped features associating a significantly less polished surface finish with surrounding surface region 106 than the surface finish disposed across accessory region 102. In some embodiments accessory region 102 can be disposed slightly lower than surrounding surface region 106 as a result of increased material removal resulting from additional polishing operations. FIG. 1D shows one embodiment of gradual transition region 108 achieved after a lapping operation. Gradual transition region 108 can be spread over a relatively short distance in this embodiment. As will be discussed below this can be achieved by varying a lapping path of a lapping tool used to create gradual transition region 108. This embodiment can be desirable when a shorter lapping operation is desired, and/or when only a minimal amount of material removal is desired. In some embodiments a short gradual transition region can result in a more noticeable transition than the one similar to gradual transition region 108 as depicted in FIG. 1E. FIG. 1E shows a relatively more gradual transition region 108. While a longer transition region results in additional material removal it can also beneficially allow for a more seamless gradual transition region 108. Such an effect can be desirable when such a surface should have little or no tactile cues to a holder of aluminum housing 100 of changes in surface finish.
FIG. 2 illustrates one embodiment of lapping machine assembly 200. Lapping machine assembly 200 includes lapping tool 202. In this embodiment of lapping machine assembly 200 lapping tool 202 is mechanically coupled to tool holder 204. Tool holder 204 is configured to maneuver lapping tool 202 in the Z-axis. By maneuvering lapping tool 202 in the Z-axis lapping tool 202 can be put into direct contact with aluminum housing 100. Tool holder 204 can also be configured with sufficient power to exert force on aluminum housing 100 by lapping tool 202. Exertion of force upon aluminum housing 100 can be regulated by a force sensor. The force sensor is used to ensure a consistent amount of pressure is exerted between lapping tool 202 and aluminum housing 100. The force sensor can be any force sensor capable of regulating pressure between lapping tool 202 and aluminum housing 100 such as for example a weight based, spring based or even pneumatically driven force sensor. Aluminum housing 100 can be mechanically coupled to stage 206. Stage 206 can be configured to translate aluminum housing 100 in any direction within an X-Y plane during a lapping operation. The X-Y plane can be defined as a plane parallel to the surface of housing 100. In some configurations in addition to translation of aluminum housing 100 within the X-Y plane stage 206 can be configured to rotate housing 100 during the lapping operation. This rotation motion can maintain a surface portion of aluminum housing 100 within the X-Y plane while the stage also maneuvers aluminum housing 100 in an X-direction, a Y-direction or a combination of both directions during a lapping operation. Rotation of aluminum housing 100 can be in an axis of rotation not in alignment with an axis of rotation associated with lapping tool 202. By establishing a small mismatch between the rotational axes of aluminum housing 100 and lapping tool 202 while simultaneously maneuvering housing 100 along a lapping path within the X-Y plane, the resulting path of lapping tool 202 across the surface of aluminum housing 100 can be randomized. For example, moving aluminum housing 100 in a star shaped or spiral pattern while aluminum housing 100 is being rotated can result in a randomized, lapping path.
FIG. 3 illustrates a perspective view of one embodiment of lapping tool 202. Lapping tool 202 includes lapping pad 302. Lapping pad 302 is an abrasive pad suited to match desired surface characteristics of the surface of the substrate to which it will be applied. In one set of trials lapping pads having thicknesses of between about 1 and 5 mm and diameters of between 35 and 50 mm were used. Dimensions of lapping pad 302 ultimately depend upon the size of the area over which a polishing effect is desired. Polishing pad 302 is mechanically coupled to lapping plate 304. Lapping plate 304 has a lower surface sized to match lapping pad 302. Lapping pad 304 can be configured to spin at rotational speeds of between 400 and 1200 rpm, while in some embodiments aluminum housing 100 (not shown) spins relatively slowly at between about 10 and 30 rpm. Lapping plate 304 also includes slurry delivery channels which will be more fully detailed in subsequent drawings. Lapping tool 202 also includes slurry delivery fitting 306 which allows slurry to be delivered to a lapping surface by the lapping tool.
FIG. 4A illustrates a cross-sectional side view of lapping tool 400. Lapping tool 400 includes lapping pad 402 and lapping plate 404 as previously discussed. Lapping tool 400 also includes slurry conduit 406 with an accompanying slurry delivery inlet 408. Slurry conduit 406 routes slurry from slurry inlet 408 to lapping pad 402. This routing system can keep lapping pad 402 and a surface of aluminum housing 100 well covered in slurry during a lapping operation. However, through trials it was determined that a gravity feed alone is generally not enough to induce continuous flow of slurry to a lapping surface. When slurry conduit 406 is configured to run straight down the center of lapping tool 400 centrifugal force can cause the slurry to become trapped in slurry conduit 406. Consequently, slurry conduit branches 410 can be built into lapping tool 400. Slurry conduit branches arranged in a manner so that the branches are not perpendicular to rotation of lapping plate 404 can use the centrifugal force incidental to the spinning motion of lapping plate 404 to actually increase flow of slurry to a surface undergoing a lapping operation. In one embodiment a rate of between 50 and 100 mL/min of slurry was found to be sufficient for a lapping operation. It should be noted that in addition to gravity fed slurry delivery that pressurized slurry delivery can also be used to overcome problems with centrifugal force and through tool slurry delivery.
FIG. 4B illustrates lapping tool 450 configured to deliver slurry to an increased number of locations across a surface of lapping pad 402 by having a number of slurry conduit branches 410 distributed across the surface of lapping plate 404. In this way slurry delivery to lapping pad 402 can be accomplished in a more even manner. It should be noted that lapping pad 402 includes chamfered edges 412 as depicted. In a normal lapping operation lapping pad will be held substantially parallel to the surface upon which it is lapping. In the event of a small misalignment chamfered edges 412 can reduce the likelihood of an edge of lapping pad 402 putting a mark or blemish in a surface portion of aluminum housing 100. In some embodiments lapping plate 404 can have rounded corners 414 to further reduce the likelihood of scraping of aluminum housing 100 by lapping plate 404.
FIG. 4C illustrates a lapping tool 460 configured with a variable flexibility lapping plate 462. In one embodiment lapping plate 462 can be configured to have a rigid central portion 464 coupled to a flexible peripheral portion 466. In this way peripheral portions of lapping pad 402 can experience a reduced amount of force, thereby resulting in a smaller amount of material removal towards an edge portion of the cutting tool, thereby achieving a more gradual feathering effect than might otherwise be possible with a solid and rigid lapping plate 462. In another embodiment lapping plate 462 can be a composite plate having gradually decreasing rigidity moving from a central portion of lapping plate 462 to an outer edge portion of lapping plate 462, thereby achieving a similar increase in feathering performance. Furthermore, lapping pad 402 can assume a dome shape as illustrated, thereby reducing force applied by peripheral portions of lapping pad 402, thereby further increasing feathering performance of lapping tool 460.
FIG. 4D illustrates an embodiment in which lapping plate 482 is one solid metal material. For example, lapping pad 482 can be a single piece stainless steel lapping plate. Furthermore, slurry delivery conduits 408 can be arranged laterally outside the lapping tool. Slurry conduits 408 can deliver slurry around a peripheral portion of lapping tool 480, thereby covering the lapping path of the lapping tool with slurry prior to a lapping operation. While two slurry conduits are shown in this illustration it should be noted that any number of slurry conduits 408 can surround lapping tool 480 thereby evenly spreading slurry in any direction lapping tool 480 is traversing. Lapping pad 484 can be configured to have a broader diameter than lapping plate 482. Since this results in lapping pad 484 extending past an edge portion of lapping pad 482 a smaller amount of pressure can be asserted on an underlying portion of aluminum housing 100, thereby increasing a feathering effect of lapping tool 480.
FIG. 5 illustrates a top view of one possible center weighted path 502 that can be employed during a lapping operation. A stage can be configured to translate aluminum housing 100 in a manner matching lapping path 502 with respect to lapping tool 504. Lapping tool 504 makes a swath 506 as it translates across aluminum housing 100. Lapping path 502 works particularly well because it aligns an edge portion of lapping tool 504 with a central portion of accessory region 102. Since trials have shown that peripheral portions of lapping tool 504 remove material more quickly than central portions of lapping tool 504 this configuration results in hitting a central portion of accessory region 102 more heavily than outlying portions of accessory region 102. Furthermore, since lapping path 502 minimizes time spent by lapping tool 504 at various peripheral portions of aluminum housing 100 a smooth feathered pattern can be achieved across abrupt transition region 104, thereby creating a gradual transition region creating an illusion of a completely smooth surface for aluminum housing 100. Furthermore, in some cases even a complex shape like the one depicted may result in minor linear track marks being scribed into a surface portion of aluminum housing 100. By rotating aluminum housing 100 in direction 508 while path 502 is being traced lapping path 502 can be further randomized essentially creating curved lapping segments instead of straight lines paths into aluminum housing 100, thereby making lapping paths much more difficult to discern.
It should be noted that in some embodiments multiple accessory regions 102 can be present on one surface of aluminum housing 100. Given such a configuration a single lapping operation can be designed to cover multiple accessory regions 102 when they are in close proximity to one another. For example, in one embodiment an aluminum housing 100 with a shiny corporate logo proximate to a shiny line of text can be desired. When the text is in proximity to the logo abrupt transition regions 104 of both the logo and the text can be removed in a single lapping operation. It should also be noted that in a more complex configuration an extra degree of freedom can be added to a lapping machine assembly allowing a lapping operation to be applied across a three dimensional surface. For example, a spline or curve shaped surface can also include accessory regions. As with a flat surface, abrupt changes between a surface finish of an accessory region and the remaining portions of a housing can result in visual and tactile distractions. The extra degree of freedom in the stage can allow blending across an abrupt transition region, thereby allowing aforementioned techniques such as the lapping path to be applied to a three dimensional surface.
FIG. 6 illustrates alternative lapping paths that can be used with previously described embodiments. As depicted orbital, spiral, race track and figure eight patterns can all be used to apply more polishing effect on an inner portion of an accessory region while more lightly polishing peripheral portions of an accessory region, thereby creating a gradual transition region or feathering effect between coarser and smoother portions of an aluminum housing. In one embodiment, the rotational speed and the translational speed along the continuous path of the lapping tool can be fixed. In some embodiments, one or more properties of the lapping tool can be selected (fixed or variable along the cutting path) from the following: the properties can include but not limited to (1) feed rate (translational speed in one or more of the x-axis, or y-axis directions), (2) spindle speed (rotational speed), (3) lapping tool shape and size, e.g. diameter, and (4) lapping tool cutting material. The properties of the lapping tool can be chosen to affect the polishing time and resulting properties of the cut surface of aluminum housing 100. The rotational and translational speeds can be selected to minimize polishing time while ensuring a quality of surface cut by the polishing tool that can result in a preferred surface finish.
FIG. 7 illustrates a flow chart detailing a representative lapping process 700 in accordance with the described embodiments. Process 700 can begin at 702 by pre-measuring selected surface characteristics such as surface roughness. The measuring can be carried out by performing a 3D scan, for example, and taking various contour measurements. At 704, the surface area to be lapped is processed by a lapping tool. During the t lapping process, slurry can be transported through the lapping tool and selectively delivered to a portion of the spot lapping region during the spot lapping process. In one embodiment, the lapping tool can include force sensors used to monitor in real time a force applied by the lapping tool on the surface. In one embodiment, the lapping tool can have a lapping pad coupled to a lapping plate having a rigid central portion and a more flexible peripheral portion. A force applied by the lapping pad corresponding to the rigid central portion can be a maximum and the force can then be reduced at lapping pad portions corresponding to the more flexible peripheral portion. In one embodiment, the lapping tool can be translated along a lapping path with respect to the housing. A lapping path can include orbital motions and star shaped motions that can be used in conjunction with rotation of the housing to facilitate a smooth transition region between the spot lapping region and a remainder of the surface of the housing. At 706, surface characteristics are measured and if at 708 are determined to be acceptable then process 700 ends otherwise control is passed back to 704.
The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. Various aspects of the described embodiments can be implemented by software, hardware or a combination of hardware and software. The described embodiments can also be embodied as computer readable code on a computer readable medium for controlling manufacturing operations or as computer readable code on a computer readable medium for controlling a manufacturing line used to fabricate thermoplastic molded parts. The computer readable medium is any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include read-only memory, random-access memory, CD-ROMs, DVDs, magnetic tape, optical data storage devices, and carrier waves. The computer readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.
The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the invention. Thus, the foregoing descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.
The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.

Claims

What is claimed is:

1. An apparatus for creating a gradual transition region between an accessory region and a surrounding exterior surface region of a housing, the apparatus comprising:

a lapping tool, the lapping tool comprising:

a lapping pad, comprising:

a centerpoint surrounded by a central portion, and

a peripheral portion,

wherein during a lapping operation the centerpoint of the lapping pad is compelled to follow a lapping path, the lapping path comprising a plurality of lapping segments, each lapping segment substantially crossing the accessory region at an angle different than a preceding lapping segment and each lapping segment putting the peripheral portion of the lapping pad in tangential contact with a central area of the accessory region, thereby creating the gradual transition region.

2. The apparatus as recited in claim 1, wherein the created gradual transition region provides a gradual transition between a fine finish associated with the accessory region and a coarser finish associated with the surrounding exterior surface region.

3. The apparatus as recited in claim 2, wherein a geometric configuration of the polishing path causes the peripheral portion of the lapping pad to come in more frequent contact with the central area of the finished accessory region than with any other portion of the surrounding exterior surface region.

4. The apparatus as recited in claim 3, wherein the lapping tool further comprises a lapping plate mechanically coupled to the lapping pad, the lapping plate comprising:

a rigid central portion; and

a flexible peripheral portion mechanically coupled to the rigid central portion,

wherein the flexible peripheral portion allows a greater force to be applied across the central portion of the lapping pad and smaller force towards the peripheral portion of the lapping pad during a lapping operation.

5. The apparatus as recited in claim 3, wherein the lapping tool further comprises a lapping plate mechanically coupled to the lapping pad, the lapping plate comprising:

a composite plate having a rigid central portion and a more flexible periphery, the change in rigidity occurring gradually between the rigid central portion and the periphery.

6. The apparatus as recited in claim 3, wherein the housing is mechanically coupled to a stage having at least four degrees of freedom, the stage configured to maneuver the housing substantially parallel with respect to the lapping pad, the maneuvering of the stage compelling the lapping pad to follow the lapping path with respect to the housing.

7. The apparatus as recited in claim 6, wherein the stage is configured to rotate around a first axis offset from a second axis of rotation associated with the lapping plate as it continues to compel the lapping tool to follow the lapping path by translation in X and Y axes,

wherein the offset between the first and second axes randomizes the lapping path.

8. The apparatus as recited in claim 7, wherein the lapping path has a star shaped geometry.

9. The apparatus as recited in claim 7, wherein the housing includes a plurality of accessory regions and the polishing path causes the lapping pad to create a gradual transition region covering the plurality of accessory regions.

10. The manufacturing method as recited in claim 6, wherein a diameter dimension of the lapping pad is between about 35 and 45 mm.

11. A manufacturing method, comprising:

mounting a housing to a stage, the housing comprising:

a first region,

a second region surrounded and defined by the first region, and

a transition region disposed between the first region and the second region;

positioning a lapping tool in physical contact with a portion of the second region during a lapping operation, the lapping tool comprising a lapping pad having a central portion and a peripheral portion; and

finishing the transition region by causing the lapping pad to follow a lapping path, the lapping path comprising a plurality of lapping segments, each lapping segment substantially crossing the second region at an angle different than a preceding lapping segment and each lapping segment putting a peripheral portion of the lapping pad in tangential contact with a central area of the second region.

12. The manufacturing method as recited in claim 11, wherein the finished transition region provides a gradual surface texture transition between the second region and the first region.

13. The manufacturing method as recited in claim 12, further comprising:

performing a three dimensional scan of the housing prior to beginning a lapping operation,

wherein the lapping path can be adjusted to target the transition region.

14. The manufacturing method as recited in claim 12, wherein after a lapping operation a subsequent lapping operation is performed if the transition region is not completely finished.

15. The manufacturing method as recited in claim 12, wherein the finishing the transition region comprises rotating the housing in an axis of rotation offset from the lapping tool axis of rotation while the lapping path is being followed.

16. A lapping assembly, comprising:

a lapping tool comprising a rotating lapping plate coupled to a lapping pad;

a force sensor coupled to the lapping tool for regulating pressure exerted by the lapping tool; and

a stage configured to maneuver a housing in a plane substantially parallel with the lapping pad during a lapping operation, the housing having an exterior surface with an accessory region and a surrounding surface region,

wherein during a lapping operation the lapping pad is compelled to follow a lapping path, the lapping path comprising a plurality of lapping segments, each lapping segment substantially crossing the accessory region at an angle different than a preceding lapping segment and each lapping segment putting a peripheral portion of the lapping pad in tangential contact with a central area of the accessory region, thereby creating a gradual transition region between the accessory region and the surrounding surface region.

17. The lapping assembly as recited in claim 16, wherein the stage has at least 6 degrees of freedom, and wherein the degrees of freedom of the stage allow the lapping tool to establish the gradual transition region across a three dimensional curved surface portion of the housing.

18. The lapping assembly as recited in claim 16, wherein the lapping tool has a chamfered edge portion configured to prevent scratching of the metal housing when a misalignment between the lapping tool and the metal housing takes place.

19. The lapping assembly as recited in claim 16, wherein the lapping tool further comprises a slurry delivery conduit having a plurality of slurry delivery branches configured within the lapping plate,

wherein the rotational motion of the lapping tool draws slurry down through the slurry conduit as a result of a geometrical configuration of the plurality of slurry delivery branches.

20. The spot lapping assembly as recited in claim 16, wherein the housing is an aluminum housing and the accessory region has a mirror finish prior to the lapping operation.