Electric rotary shaver

An electric rotary shaver including a substantially circular disk form outer cutter, which has hair entry openings, and an inner cutter, which rotates while making sliding contact with the inner surface of the outer cutter; and the inner cutter including an inner cutter base, which is made of a synthetic resin and comprised of a boss that engages with a rotary shaft of the shaver and cutter blade supports that extend radially outward from the boss, and a plurality of cutter blade sections, which have a cutter blade and are installed on the cutter blade supports. The cutter blade sections can be formed in a shape of a ring to make a cutter blade ring so that the cutter blade ring is disposed on the cutter blade supports.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric rotary shaver that includes an inner cutter that rotates while making sliding contact with the inner surface of a substantially circular disk form outer cutter that has a plurality of openings formed on the top surface.

2. Prior Art

In a typical electric rotary shaver, numerous small hair entry openings (e.g., slits) are formed in the top surface of a substantially circular disk form outer cutter that has in its inside a circular track (groove), and an inner cutter is provided so that it rotates while causing its blades (cutter blades) that are integrally disposed on this inner cutter to make sliding contact with the inner surface of this outer cutter. Such an electric rotary shaver is disclosed in, for instance, Japanese Patent Application Laid-Open (Kokai) No. 06-238070.

More specifically, in the conventional inner cutter disclosed in the above prior art, an inner cutter main body made of metal is fastened to a boss that is made of a synthetic resin.

FIG. 10is a perspective view of the inner cutter disclosed in the above-identified prior art.FIG. 11is a perspective view of the outer cutter that is used with this inner cutter10.FIG. 12is a side view of the inner cutter with a part of the inner cutter omitted.FIG. 13is a partially sectional side view of this inner cutter.FIG. 14is a cross sectional side view of an assembled inner cutter and outer cutter of the prior art.

The outer cutter12is, as seen fromFIG. 11, made of metal and in a substantially circular disk shape. In other words, this outer cutter12is made so that a circular plate is bent at the circumferential edge so as to have a shallow substantially dish-form shape or substantially inverted dish-form shape, numerous small hair entry openings constituting slits14are formed in this outer cutter12in a radial pattern, and an annular groove16is further formed in this outer cutter. This groove16extends across the slits14in the vicinity of the midpoint of each slit14. As a result, the outer cutter12has two annular sections (or annular tracks)12A and12B (seeFIG. 14) on either side of this groove16. A structure in an outer cutter that has such two tracks12A and12B is called a double track structure.

The boss18(seeFIG. 10) of the inner cutter10is made of a POM (polyoxymethylene) resin, e.g., “Delrin” (Registered Trademark), a product of DuPont, etc.; and the lower portion of the boss18has an inverted dish form portion that opens at the bottom. As seen fromFIG. 12, an engaging hole22with which a rotary shaft (not shown in the drawings) of the shaver is engaged from below is formed in this inverted dish form portion20. A columnar center projection24is disposed in the center of the upper surface of the boss18.

The inner cutter main body26(seeFIG. 10) is obtained by stamping and bending a metal plate, and it has a substantially pinwheel-form shape. More specifically, the inner cutter main body26has ten mutually separated raised portions30, which are raised from the outer circumference of a circular plate portion28, and blade portions32, which are formed by further bending the raised portions30in the radial direction of the boss18. The center projection24of the boss18passes through the center of the circular plate portion28and is securely fastened by hot-crimping to the upper surface of the inverted dish form portion20of the boss18.

The upper portion of each one of the blade portions32of the inner cutter main body26is formed into a bifurcated shape, and the ends of the bifurcated blade portions respectively form cutter blades34. The two cutter blades34are respectively set from below (i.e., from the inside) in the two annular sections12A and12B of the double-track outer cutter12. Accordingly, when the inner cutter10comprising substantially the boss18and inner cutter main body26is rotated by the rotary shaft (not shown in the drawings) connected to the motor installed in the shaver main body (not shown in the drawings), the cutter blades34run while being in contact with the inner surfaces12aand12bof the annular sections12A and12B of the outer cutter12(seeFIG. 14). As a result, hair (whiskers, etc.) entering through the slits14of the outer cutter12is cut by the cutter blades34of the rotating inner cutter11.

The upper end portions of the cutter blades34of the inner cutter10shown here are inclined so that these upper end portions are offset further in the direction of rotation of the inner cutter10than the lower portions of the blade portions32. In other words, the upper end portions are inclined toward the front in terms of the rotating direction of the inner cutter10.

Furthermore, as shown inFIGS. 12 and 13, recesses36are formed in the surfaces of the respective cutter blades34so that the recesses36face the counter-rotation direction, so that a part of each of the recesses36reaches the upper end surface (i.e., the cutting surface that makes sliding contact with the inner surface of the outer cutter12) of the each cutter blades34. These recesses36prevent shaving debris and dirt from adhering to the cutter blades34, and it also functions to decrease the area of contact between the cutter blades34and the outer cutter12, reducing the driving resistance (see the above-described cited prior art). In the present invention, however, the recess36can be omitted.

The above-described inner cutter10and outer cutter12make a pair; and, for instance, three pairs of such cutters are provided at the vertices of an equilateral triangle in the cutter head of a shaver. Three inner cutters10are rotationally driven by a motor installed in the main body of the shaver. A shaver with two pairs of inner and outer cutters and a shaver with only a single pair of such cutters are also possible.

As seen from the above, in the conventional inner cutter, the entire inner cutter main body26is made by press-stamping a single metal plate and then bending this plate approximately 90° at the two places A and B as shown inFIGS. 12 and 13and14. When the number of locations where such bending is performed is thus large, the distance from the center of the inner cutter10to the cutter blades34, especially the distance to the inner circumferential edges and outer circumferential edges of the cutter blades34, tends to become non-uniform, resulting in that the inner and outer circumferential edges of the cutter blades34contact the inner and outer circumferential walls12cand12dand the inner and outer circumferential walls12eand12fof the respective annular sections12A and12B of the outer cutter2. This leads to problems such as an aggravation of operating noise and deterioration in sharpness due to an expansion of the annular sections' width of the outer cutter12. Furthermore, it is necessary, for making inner cutters, to use a special metal material that has good pressing characteristics and that can be hardened.

Furthermore, in rotary shavers, a frictional resistance force generated by the sliding motion between the cutter blades34of the inner and the outer cutter12and a resistance force that generates when hair is cut are applied to the cutter blades34. Accordingly, the inner cutter main body26must have a sufficient thickness and a high rigidity so that the cutter blades34do not vibrate by such resistance forces. Ordinarily, an SUS420J2 metal plate with a thickness of 0.5 mm is used for inner cutters of rotary shavers. In cases where such a thick metal material is pressed (subjected to stamping and bending), the working precision tends to be poor, and problems such as the occurrence of vibration, increase in operating noise, deterioration of sound quality and deterioration of sharpness due to biased wear of the cutter blades tend to occur.

In order to increase the working precision, it is desirable to make the length of the bent portions (A, B) formed by pressing as small as possible. However, if the length of these portions is shortened, the width of the raised portions30is naturally reduced, which is disadvantageous from the standpoint of preventing vibration of the cutter blades34. If the distance between the tip end portions of the cutter blades34to which a resistance force is applied and the bent portions (A, B) is large, the stress applied to the bent portions (A, B) increases; and this is disadvantageous from the standpoint of vibration. However, in inner cutters having the conventional structure, there are limitations in shortening this distance.

Thus, because of the structural problems such as poor pressing precision, a large number of bent portions and the like, problems such as vibrations in the cutter blades, resonance of various parts, an increase in operating noise and a deterioration in sound quality have been unavoidable.

SUMMARY OF THE INVENTION

The present invention was made in light of the facts described above.

The object of the present invention is to provide an electric rotary shaver in which, with a new structure of the inner cutter main body, the pressing precision during the making of the inner cutter is high due to the reduced number of places where bending is performed by pressing, the deviation of rotation of the respective cutter blades of the inner cutter from a true circle is prevented, the operating noise is suppressed and the inner cutter's rotating sound quality is high due to the reduced vibration of the cutter blades, and a deterioration in sharpness of the cutter blades caused by biased wear of the cutter blades is prevented.

The above object is accomplished by a unique structure of the present invention for an electric rotary shaver that includes a substantially circular disk form outer cutter, which has hair entry openings in its top surface, and an inner cutter, which rotates while making sliding contact with the inner surface of the outer cutter; and in the present invention,the outer cutter is formed inside thereof with an annular track; andthe inner cutter is comprised of:an inner cutter base which is made of a synthetic resin and is comprised of a boss that engages with a rotary shaft of the shaver and cutter blade supports that extend outward from the boss, the boss and the cutter blade supports being formed integrally, anda plurality of cutter blade sections which are formed with a cutter blade that makes sliding contact with the annular track and which are provided on the cutter blade supports.

In the present invention, the boss and cutter blade supports are formed as an integral unit of the inner cutter base that is made of a synthetic resin and a plurality of cutter blade sections of metal-made are securely held on the cutter blade supports. Accordingly, the need to support the respective cutter blade sections on a circular plate portion or raised portions as in the conventional inner cutter main body is eliminated, and the formation of numerous press-bent portions (A, B) seen in the conventional inner cutter main body becomes unnecessary, and in addition the inner cutter has a high pressing precision by the reduction of the number of bent portions.

Furthermore, the present invention provides several advantages. Not only that the working precision is high but also the vibration of the cutter blades is reduced and a vibration absorbing effect by the synthetic resin made cutter blade supports is assured. Thus, operating noise is reduced, and the sound quality of the rotating inner cutter is high. Furthermore, biased wear of the cutter blades caused by vibration of the cutter blades is suppressed, and deterioration in sharpness is also prevented. Moreover, since the cutter blades tend not to vibrate, it is possible that the cutter blades have a reduced thickness, so that the amount of special expensive metal materials used is reduced.

The cutter blade supports can be formed by a plurality of arms that extend radially from the boss. This structure reduces the weight of the inner cutter; and since shaving debris, etc. made by the cutter blades drops between the radial arms, the shaving debris tends not to adhere to the inner cutter, facilitating the cleaning of the inner cutter and the shaver. The cutter blade supports, however, can be formed as a circular plate as a whole. Furthermore, the number of radial arms can be less than the number of cutter blades; and in this structure, each arm holds more than one (or a plurality of) cutter blade section.

For an electric rotary shaver that has an outer cutter formed inside thereof with a single annular track, the plurality of cutter blade sections can be connected in a ring form to form a cutter blade ring, and this formation of the cutter blade sections facilitates the working (forming) of the cutter blade sections and the attachment of the cutter blade sections to the cutter blade supports. In addition, by way of setting the portion near the cutter blade sections of the cutter blade ring to be held on the upper surfaces of the cutter blade supports, it is possible to prevent the cutter blade sections from vibrating more efficiently. For an electric rotary shaver that has an outer cutter formed inside thereof with a plurality of concentric annular tracks, each of the cutter blade sections has cutter blades that are disposed side by side in the radial direction of the inner cutter, and such cutter blade sections are connected to each other to form a cutter blade ring, and this cutter blade ring is provided on the cutter blade supports. Each of such cutter blade sections can be in a letter Y-shape, the cutter blades are provided in the bifurcated portions of this Y-shaped cutter blade section, and such cutter blade sections are connected to each other at their connecting portions thus forming the cutter blade ring.

The plurality of cutter blade sections can be respectively provided on the respective cutter blade supports. A plurality of cutter blade sections can be combined so as to form a group, so that a plurality of cutter blade groups are provided on the cutter blade supports. The cutter blade supports can be in the shape of a plurality of arms, so that the cutter blade sections in the same number of the cutter blade supports are respectively provided on the respective cutter blade supports. A plurality of cutter blade sections can be combined to form several groups, the cutter blade supports are formed in the same number as the number of groups. The cutter blade sections are provided on the cutter blade support by hot-crimping, or they can be insert-molded on the inner cutter base when the inner cutter base is formed by injection-molding. Furthermore, fastening of the cutter blade sections by means of a bonding material or a combined use of a bonding material is also possible. In addition, inner cutter holding members for holding the cutter blades can be inserted in the inner cutter base, so that the cutter blades are held on the inner cutter holding members.

When the cutter blade sections take the form of the cutter blade ring, the inner circumferential portion of this cutter blade ring can be held on or fastened to the boss. In this structure, since the cutter blade ring is held by the boss and by the cutter blade supports, the cutter blade sections are fastened much more securely, and the vibration of the cutter blades is reduced even further.

The outer cutter that is used with the inner cutter described above can be formed with numerous slits that extend in the radial direction of the outer cutter. An outer cutter in which the slits are obliquely oriented with respect to the radial direction of the outer cutter or an outer cutter in which the slits are curved or bent into a wave shape running more or less in the radial direction can also be used.

For an electric rotary shaver that has an outer cutter formed inside thereof with a single annular track, the inner cutter can be designed so that a part of the central portion of each one of the cutter blade sections of the cutter blade ring that is obtained from, for instance, a metal plate, is cut (by, for instance, press-die-stamping) in the circumferential direction of the cutter blade ring and bent upward to form the cutter blade. In the actual manufacturing process of such a cutter blade ring, the cutter blade ring is formed by press-die-stamping a metal plate into a substantially ring-form shape and by subsequently or simultaneously bending upward the portions that constitute the cutter blades.

For the electric rotary shaver that has an outer cutter formed inside thereof with a single annular track, the inner cutter can also be designed so that a part of the outer circumferential edge of each one of the cutter blade sections of the cutter blade ring is cut in the circumferential direction of the cutter blade ring and bent upward to form the cutter blade in a somewhat cantilever configuration.

In addition, for an electric rotary shaver that has an outer cutter formed inside thereof with two annular tracks, the inner cutter can be designed so that the cutter blade ring is comprised of a plurality of cutter blade sections connected to each other to form a cutter blade ring, and a part of the outer circumferential edge of one of the cutter blade sections is cut in the circumferential direction of the cutter blade ring and bent upward to form the cutter blade and a part of the inner circumferential edge of the next cutter blade section is cut in the circumferential direction of the cutter blade ring and bent upward to form the cutter blade. In other words, the cutter blade sections of the cutter blade ring are alternately cut along the inner and outer circumferential edges, so that the cutter blade ring has the outer circumferential cutter blades and inner circumferential cutter blades that are alternately displaced.

DETAILED DESCRIPTION OF THE INVENTION

InFIGS. 1,2and3, the reference numeral100denotes the inner cutter according to one embodiment of the present invention, and this inner cutter100comprises an inner cutter base102and a cutter blade ring104that are joined to form an integral unit.

The inner cutter base102is comprised of a boss106and eight cutter blade supports108. The cutter blade supports108are in the shape of a plurality of arms that extend radially outward from the boss106. The boss106and the arm-shaped cutter blade supports108are integrally molded from a synthetic resin. A POM (polyoxymethylene) resin is an ideal material for the synthetic resin that is used for the boss and cutter blade supports. The tip ends of all of the arms or cutter blade supports108are bent upward, and the upper surfaces of the cutter blade supports108are on an imaginary plane Y that is perpendicular to the rotational axis X (FIG. 2) of the inner cutter100.

Projections110and112protrude from the upper surface of each one of the cutter blade supports108. The projections110secure the cutter blade ring104on the cutter blade supports108by hot-crimping, and the projections112are used for positioning the cutter blade ring104.

A columnar center projection114protrudes from the center of the upper surface of the inner cutter base102. The center projection114engages with a recessed portion (not shown in the drawings) formed in the center of the inner surface of the outer cutter (such as one shown inFIG. 9) when the inner cutter100is set in the outer cutter and thus prevents eccentricity of the inner cutter100with respect to the outer cutter. In other words, the center projection114prevents rotational wobbling of the inner cutter100.

As best seen fromFIG. 3, the cutter blade ring104is comprised of substantially Y-shaped cutter blade sections116connected in a ring shape; and each one of the substantially Y-shaped cutter blade sections116is comprised of a connecting portion120and a pair of cutter blades118that are to be positioned in two concentric circular sections (see, for instance,FIG. 14) of the outer cutter. The two cutter blades118in a bifurcated shape or letter Y-shape are tilted forward in the direction of rotation y of the inner cutter100, and a recess122is formed in the surface of each cutter blade118so that it faces the direction opposite from the direction of rotation y. The Y-shaped cutter blade sections116are connected to each other by the connecting portions so that the connecting portions extend between the bifurcated cutter blades118, thus forming the ring shape.

This cutter blade ring104is formed by press-die-stamping a metal plate into a substantially ring-form shape and subsequent or simultaneous bending of the portions constituting the cutter blades118. Furthermore, the recesses122are formed in the cutter blades118and cutter blade fastening holes124are formed in the cutter blades116; and this working for the recess and fastening holes is performed at the same time as the press die stamping, and it can be dome in a separate process.

Due to the structure described above, the cutter blade ring104is obtained with a small number of press-working. Furthermore, since the cutter blades118are bent (raised) upward by small angles as can be seen fromFIG. 3, the stress applied to the metal material for the cutter blade ring114is small, and the characteristics of the metal material (especially the press-working characteristics) are low. In the present invention, furthermore, as will be described below, since the cutter blade sections116are directly fastened to the cutter blade supports108, vibration of the cutter blade sections116is suppressed. Accordingly, thin metal plate can be used for the cutter blade ring114, and the press-working characteristics are high in this regard as well.

The cutter blade ring104described above is fastened to the cutter blade supports108of the inner cutter base102by hot-crimping. More specifically, the cutter blade ring104of the shown embodiment has a total of eight inner cutter fastening holes124formed at positions that correspond to the projections110of the arms or cutter blade supports108, and these projections110are passed through the inner cutter fastening holes124of the cutter blade ring104, and the upper ends (protruding ends) of the projections10are crimped (hot-crimped) by compressing these upper ends while applying heat thereto. InFIGS. 1 and 2, the reference numeral110A indicates the hot-crimped portions. The other projections112on the cutter blade supports108are used for positioning the cutter blade ring104by being contacted the side edges of the connecting portions120as shown inFIG. 1.

After the cutter blade ring104has thus been fastened in place, the tip ends of all of the cutter blades118are ground to form cutting edges. Of course, the cutter blade ring104is heat-treated at an appropriate time following the press-working.

The boss106of the inner cutter base102of the inner cutter100is formed with an engaging hole126(seeFIG. 2) that is to be engaged with a corresponding rotary shaft (not shown in the drawings) of the shaver; and after being covered by the outer cutter (seeFIG. 9), the inner cutter is rotationally driven in use of the shaver.

In the above embodiment, the cutter blade supports108extend radially or they are spacedly provided in the circumferential direction of the inner cutter100; and when the cutter blade ring104is provided on the inner cutter base106, a pair of cutter blades118are located between two adjacent cutter blade supports108. Accordingly, the shaving debris made by the cutter blades118smoothly fall down through the gaps between the cutter blade supports118, so that shaving debris tends not to adhere to the cutter blades118, and cleaning is facilitated.

FIGS. 4 and 5show another embodiment of the present invention

As shown inFIG. 4, in the cutter blade ring202of this embodiment, the portions that correspond to the cutter blade sections116inFIGS. 1 and 3are connected and integrated by a flange portion204located on the inner side of the ring202.

A small-diameter portion206which is formed into a substantially cup-form shape by deep-drawing is formed in the center of the flange portion204, and an opening208is formed in the bottom of this small-diameter portion206. In the edge of this opening208, as seen fromFIG. 4, two different circular arcs are alternately formed at equal intervals, with four of each of these two types of circular arcs being formed. Cutter blades210, connecting portions212and cutter blade fastening holes214are formed in the cutter blade ring202in the same manner as those in the cutter blade ring104shown inFIGS. 1 and 3.

As shown inFIG. 5, the inner cutter base216has cutter blade supports220and projections222. The cutter blade supports220radially extend from the boss218, and the projections222protrude from the upper surfaces of the tip ends of the cutter blade supports220. The cutter blade ring202is carried on the cutter blade supports220with the cutter blade fastening holes214aligned with the projections222. The tip ends of the projections222that protrude from the cutter blade fastening holes214are hot-crimped so that they hold the cutter blade ring202.FIG. 5shows the state after the hot-crimping of the projections222is done. A columnar center projection224of the boss218is passed through the central opening208of the cutter blade ring202, and the inner circumferential rim of the opening208is fastened to the projection224by hot-crimping. The reference numeral226inFIG. 5indicates the hot-crimped portion.

In the structure shown inFIGS. 4 and 5, when the cutter blade ring202is mounted on the inner cutter base216, the portion of the cutter blade ring202located near the outer circumference is supported from beneath by the cutter blade supports220, and the portion located near the inner circumference is fastened to the vicinity of the boss218. Accordingly, the connection of the cutter blade ring202and the inner cutter base216is greatly strengthened, and the anti-vibration effect of the cutter blade ring202is high.

FIG. 6shows, in cross-section, still another structure of the inner cutter of the present invention.

In this structure, the cutter blades302of the inner cutter300are in an individual form and do not formed into a cutter blade ring, and the individual cutter blades302are inserted in a circular cutter blade support306provided on the inner cutter base304. More specifically, all of the cutter blades302are fixed in place in the mold prior to the resin-molding of the inner cutter base304, and the inner cutter base304is injection-molded in this state (insert-molding).

FIG. 7shows, in cross-section, still another structure of the inner cutter of the present invention.

In the structure ofFIG. 7, each one of the cutter blades352of the inner cutter350are fastened by way of hot-crimping to the cutter blade support356of the inner cutter base354. More specifically, the lower portions352A of the cutter blades352are bent so that the lower portions352A take a horizontal configuration and come into contact with the upper surface of the cutter blade support356, and projections358formed on the upper surface of the cutter blade support356pass through holes formed in the lower horizontal portions352A of these cutter blades352, and the protruding ends of the projections358are hot-crimped.FIG. 7shows the state after the hot-crimping of the projections358is completed.

When individual cutter blade sections302and352are provided on the inner cutter base as shown inFIGS. 6 and 7, a plurality of cutter blade sections302or352can be combined to form several groups. When the cutter blade sections form groups, the inner cutter is formed with arms (or the cutter blade supports) in the same number as the number of the groups, so that each group of cutter blade sections is provided on each arm (cutter blade support). In this structure, the top surface area of the arms differ from each other so as to match the size of the combined cutter blade sections.

FIGS. 8(a) and8(b) respectively show a part of the cutter blade rings according to the embodiment of the present invention. Each of these cutter blade rings is for an inner cutter that is used in a shaver that includes an outer cutter formed inside thereof with a single annular section (or a single annular track, not shown).

In the structure ofFIG. 8(a), the cutter blade ring400′ has a configuration in which a plurality of cutter blade sections400are connected to each other in a ring shape at the connecting portions402to form a cutter blade ring400′; and in each cutter blade section400, a cutter blade404is formed by being cut in the circumferential direction of the cutter blade ring400′ and bent upward at substantially the center of the cutter blade section400, leaving an opening406that remains after cutting of the cutter blade404. Since each cutter blade section400surrounds the opening406, the cutter blade ring400′ has an increased rigidity.

In the structure ofFIG. 8(b), a plurality of cutter blade sections420are connected to each other in a ring shape at the connecting portions422to form a cutter blade ring400″; and in each cutter blade section420, a cutter blade424is cut in the circumferential direction of the cutter blade ring400″ and bent upward along the outer circumferential edge in a somewhat cantilever configuration. This cutter blade ring400″ is narrow in width, and thus it is small in size and light in weight.

FIG. 9shows a part of the cutter blade ring according to still another embodiment of the present invention. The cutter blade ring400′″ ofFIG. 9is for an inner cutter used in a shaver that includes an outer cutter formed inside thereof with double concentric annular sections (or double concentric annular tracks, not shown).

This cutter blade ring400′″ has a configuration in which a cutter blade426is further formed in the cutter blade section420of the cutter blade ring shown inFIG. 8(b). In other words, in this cutter blade ring400′″, a cutter blade424is formed by being cut in the circumferential direction of the cutter blade ring400′″ and bent upward along the outer circumferential edge of a cutter blade section420of a ring shaped metal plate, and another cutter blade426is formed by being cut and bent upward along the inner circumferential edge of a cutter blade section428which is next to the cutter blade section420of the ring shaped metal plate, so that the outer circumferential cutter blades424and the inner circumferential cutter blades426are alternately displaced circumferentially and radially. In this structure, one cutter blade section (for instance, the cutter blade section428) for one cutter blade is a connecting portion for the next cutter blade section (for instance, the cutter blade section420), and such one cutter blade section (for instance, the cutter blade section420) for one cutter blade is a connecting portion for the next cutter blade section (for instance, the cutter blade section428). In use, the cutter blades426on the inner circumferential edge of the cutter blade ring400′″ come into contact and slide along the inner surface of the inside annular section (track) of a two-track outer cutter, and the cutter blades424on the outer circumferential edge come into contact with and slide along the inner surface of the outside annular section (track) of such a two-track outer cutter.