CH643168A5 - ANNULAR STRAWBERRY TO BE BORED WORKING IN FRONT. - Google Patents

Description

The present invention relates to an annular milling cutter working from the front.

In US Patent No. Re 28416, an annular bur is described having a plurality of teeth spaced around its (lower) leading end. Each tooth has more than 30 circumferentially offset cutting edges. The cutting edges are designed so that each of them forms its own chip. The radially innermost cutting edge extends radially across a shallow recess formed in the core between successive teeth, and the outermost cutting edge extends radially across an external groove which extends helically from bottom to top along the cutter between the successive teeth. According to the aforementioned patent, the groove has a radial depth which is equal to approximately half the thickness of the annular wall of the cutter, and the core has a thickness which is equal to approximately half the thickness of 40 the annular wall. Consequently, the radially innermost cutting edge of each tooth has a radial extent which is also equal to about half the thickness of the wall of the cutter. Thus, the groove has a radial depth which is sufficient to allow the discharge of the chips removed by the two cut edges 45.

According to another proposal of the aforementioned patent, if it is desirable to form on each tooth three cutting edges offset circumferentially so that each tooth removes three chips instead of two, the radial depth of the groove and the thickness of the core are so maintained the same as for a tooth cutter having two offsets, and the part of the wall of the cutter which corresponds to the depth of the groove constitutes two cutting edges circumferentially offset instead of a single edge. The radially outermost cutting edge is delimited by an external recess which has a relatively short axial dimension and which opens into the groove. However, the groove still has a radial dimension which is approximately equal to half the thickness of the wall of the cutter so that it can easily contain the chip removed by the radially innermost cutting edge.

60 Although the milling cutter described in the earlier patent cited above ensures a cut which is much greater than that of the annular milling cutters used previously, under certain conditions of advance and speed, the chips tend to settle in the internal hollow and in the groove. When this happens, the cut is much slower and an oversized conical hole is obtained with a coarser finish. In addition, the life of the cutting edge is significantly shortened.

The object of the invention is to remedy these drawbacks.

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The milling cutter according to the invention is defined by claim 1. Such an annular milling cutter is admirably suitable for being executed in two axially adjacent parts, assembled by interlocking so that the leading part of the milling cutter on which the teeth are produced can be made in a relatively expensive cutting tool material, such as high-speed steel, and that the body of the cutter may be made of a less expensive material, such as a fairly low alloy steel heat treated.

The annular cutter to be bored according to the preferred embodiment of the invention has an annular side wall having several teeth spaced circumferentially around its lower end and a corresponding number of helical grooves around its periphery. Each tooth has several cutting edges offset circumferentially and preferably vertically, at least two of said edges being formed on the part of the tooth which corresponds to the thickness of the core located between successive teeth and the other cutting edges being formed on the part of the tooth which corresponds to the radial thickness of the groove. The combined width of the two radially internal cutting edges is preferably greater than the combined width of the other cutting edges, in which case the thickness of the core is greater than the depth of the groove. In addition, the depth of the groove is preferably at least as large as the width of the wider of the two internal cutting edges. The thickness of the wall of the cutter is calculated to achieve a relatively narrow cutting path in order to maintain at a reasonably low value the power necessary to advance the cutter through a workpiece.

The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting examples and in which:

Fig. 1 is a perspective view of an embodiment of a milling cutter according to the present invention;

fig. 2 is a fragmentary view on a large scale of part of the cutter of FIG. 1, which is surrounded by circle 2:

fig. 3 is a fragmentary section of the strawberry along line 3-3 of FIG. 1:

fig. 4 is a fragmentary view partly in perspective and in section of a tooth of the cutter;

fig. 5 is a perspective view of another embodiment of a cutter according to the invention;

fig. 6 is a fragmentary view on a large scale of part of the cutter of FIG. 5, which is surrounded by circle 6;

fig. 7 is a perspective view in section of a tooth of the cutter shown in FIG. 5;

fig. 8 is a fragmentary large-scale view from below showing the cutter in relation to the part through which it is advanced, and FIG. 9 is a fragmentary perspective view of another cutter which is slightly modified compared to that shown in FIGS. 5 to 8.

In the drawings, the annular end milling cutter working from the front of the present invention is generally designated by 10 and comprises a body 12 and a rod 14. The body 10 has the shape of an inverted bowl and has a wall side 16 and an upper wall 18. The lower end of the side wall 16 has several cutting teeth 20 which, preferably, are uniformly spaced. A helical groove 22 extends from bottom to top around the periphery of the cutter near each tooth 20. The successive grooves 22 are separated by a cord 24 at the periphery of the cutter. In the cutter shown, the grooves and cords cover the entire length of its side wall. For some applications, the cutter ensures even more efficient work when the grooves and beads are significantly shorter than the side wall. The parts of the annular side wall of the cutter which are between the successive teeth 20 constitute webs 26. The radially external face 28 of each core 26 defines the radially internal wall of each groove 22. Each groove 22 has a front side wall 30 and a rear side wall 32.

In the embodiment of the cutter shown in figs. 1 to 4, each tooth 20 has three cutting edges 34, 36, 38. The edge 34 is at a distance forward, in the direction of rotation, of the edge 36, and the latter is at a distance towards the front, in the direction of rotation, of the edge 38. The edge 34 is located at the lower end of the rear face 40 of an internal recess 42. The upper end of the recess 42 is inclined radially towards the exterior from bottom to top at 44. The edge 36 is at the lower end of the rear face 46 of a secondary recess 48 which is formed in the core 26 in the immediate vicinity of the internal recess 44. The end upper of the secondary recess 48 is curved upward and radially outward, as indicated at 50. The edges 34 and 36 are separated by a circumferential shoulder 51 located at the lower end of the radially internal face 52 of the recess 48. The edge 38 is located at the lower end of the rear face 32 of the groove 22 and is spaced towards the rear of the edge 36 by a th shoulder 54 at the lower end of groove 22.

The underside of each tooth has undercut or bent faces 56, 58. In the operating position of the cutter, the beaded face 56 is inclined axially upward and radially inward, while the bent face 58 is inclined axially upwards and radially outwards. In addition, each of these uncurved faces is slightly inclined upwards from the respective cutting edges in a circumferential direction, for example from 5 to 20 °, to give the cutting edges the necessary draft. The two jagged faces 56, 58 form at their intersection a ridge 60 which intersects the radially outermost edge 38. Although it is possible to grind the jagged faces 56, 58 so that the ridge 60 intersects any one cutting edges, it is preferable in most cases that this ridge cuts the outermost cutting edge. As a result of the inclination of the bent faces 56, 58, the edges 34, 36, 38 are inclined axially and are offset vertically as well as in the circumferential direction.

At the lower end of each tooth, the core 26 has a radial dimension which is greater than the radial depth of the adjacent groove 22. Since the edges 34, 36, 38 are offset circumferentially as shown, when the cutter is rotated and advanced in a room, a separate chip is cut by each of the cutting edges. The relative dimensions of the cutter are such that the radial depth of the groove 22 is not appreciably less and is preferably greater than the wider of the two cutting edges 34, 36. Thus, immediately after its size, the chip formed by the cutting edge 34 is directed in the groove 22 by the radial inclination of this edge and the upper end 44 of the hollow 42. Also, immediately after its size, the chip formed by the edge 36 is directed in the groove 22 by the radial inclination of this edge and by the curvilinear wall 50 of the recess 48. The axial dimension of the secondary recess 48 is preferably not substantially greater than the axial dimension of the recess 42, so as to promote the immediate evacuation of the chip in the groove 22 and thus avoid the tendency of the chips to accumulate and settle in the hollow 48. Although the inclination of the edge 34 tends to direct the chip formed upward and outwards, the circumferential extent of the recess 42 should be small enough to prevent the chip formed by the edge 34 from coiling significantly directly into the recess 42. If the recess 42 is sufficiently small in the circumferential direction, the chip formed by the edge 34 tends to remain fairly straight and is more easily directed upwards and outwards from the hollow. The circumferential width of the internal recess 42 should preferably not be greater than approximately half the thickness of the core 26 and of the order of approximately one third of the thickness of the core 26. The circumferential dimension of the recess 42 should vary inversely proportional to the thickness of the core 26. Thus, immediately after their size, the chips formed by the edges 34, 36 are directed radially outward and axially upward in the groove 22. The chip formed by the edge 38 is also directed upward in the edge 22.

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Since each of these chips is relatively narrow and tends to form axial helices rather than radial turns, they are effectively directed radially outward by the hollows. As the helical chips move from each of the edges axially upward and radially outward in the groove 22, they tend to intertwine. As soon as the interlaced helical chips come into contact with the wall of the hole being drilled, the friction thus created tends to stop the rotation of the chips with the cutter. When this happens, the rear face 32 of the groove in which they are found comes into contact with the helical chips and pushes them upwards out of the groove. Since the chips are narrow, they can be easily compressed between the internal face 28 of the groove and the wall of the hole being drilled in the part. As the rear face 32 of each groove 22 has the shape of a continuous helix, the movement of the chips from bottom to top in the grooves is continuous, regular and unimpeded. Thus, if the recesses 42, 48 are configured and dimensioned so as to direct the chips formed by the edges 34, 36 almost directly in the groove 22 and since the displacement of the chips from bottom to top in the groove is not hindered, it is guaranteed a free movement of the chips upwards out of the groove. The free movement of the small chips along the groove is more easily carried out when the cutter is internally supplied with a pressurized coolant. In addition, because the shavings are narrow and inherently weak, they tend to break easily as they move away from the hole and therefore do not tend to wrap around the cutter and / or of the shaft or mandrel when they escape from the hole during drilling and consequently to block or hinder the subsequent escape of the cut chips subsequently. In addition, as already mentioned, if the recess 42 is narrow in the circumferential direction, the chip formed by the edge 34 has less tendency to wind, so that it is directed into the groove 22 while being better straightened. This has the effect of reducing the possibility of jamming of the chip and obstruction of the hollow or the groove.

If it is desirable to provide a slight clearance between the internal face of the wall 16 and the core during cutting, the internal face of the wall 16 can tilt outwards at an angle of about 1 ° to from its lower end, for a short distance of 12.7 mm for example, as indicated at 62 in fig. 3. Above the inclined part, the internal face of the side wall can be cylindrical as indicated in 64. Thus, at a small distance above the cutting edges, the internal face of the cutter has a play of approximately 0.203 mm in relation to the cylindrical periphery of the core which is cut in the piece. Also, as seen in fig. 3, the depth of the groove 22 can optionally be gradually increased from bottom to top by grinding the internal face 28 of the antler so that it widens radially inwards and upwards more quickly to the part 62 above the latter. This results in a radial clearance for the chip formed by the edge 38 immediately after its size. Thus, the groove may as a whole have a section which grows from bottom to top to further facilitate the ejection of the chips. Each groove can also have an increasing section so that it is circumferentially wider at its upper end than at its lower end.

The presence of a thick core, while keeping the width of all the chips at a very low value, also has the advantage of making it possible to provide an axially deeper internal hollow. Such an axially deeper recess not only facilitates a better flow of the coolant through the teeth of the cutter, but also makes it possible to maintain the sharpening of the teeth longer before a correction of the recesses becomes necessary.

It is obvious that, to reduce the power necessary to advance an annular milling cutter in a steel part, for example, it is essential that the path or the cutting groove formed by the milling cutter is relatively narrow. For a cutter intended to drill a hole in steel, a practical dimension of the thickness of the wall of the annular cutter is between approximately 4.06 and 4.57 mm. When each tooth has three cutting edges, as seen in figs. 1 to 4, and when the side wall of the cutter has a thickness of approximately 4.06 mm, the radial depth of the groove 22 can be of the order of 1.78 mm and thus the thickness of the core 26 can be about 2.29 mm. The two internal edges 34, 36 can have a width of about 1.145 mm or, if desired, the innermost edge 34 can have a width of about 1.27 mm. Thus, in the presence of a relatively thick core and a relatively thin annular wall, each of the shavings cut by the three edges can be easily contained in the groove 22. The circumferential dimension of each groove is preferably several times greater than the radial depth of each groove.

The difference between the cutter shown in fig. 5 to 8 and that of figs. 1 to 4 essentially resides in a single characteristic. In the strawberry of fig. 5 to 8, the part of each tooth which corresponds to the depth of the groove 22 has two cutting edges 70, 72 instead of just one, as shown at 38 in FIGS. 1 to 4. If the side wall 16 of the cutter has a thickness of approximately 4.06 mm, the cutter can be produced so that the groove 22 has a depth of approximately 1.63 mm and that the core 26 has a thickness of about 2.44 mm. In this case, each of the edges 34.36 may have a width of approximately 1.22 mm and each of the edges 70.72 may have a width of approximately 0.81 mm. The bent faces 56, 58 of each tooth are inclined as described above with reference to FIGS. 1 to 4 and preferably form at their intersection a ridge 74 which itself cuts the outermost edge 72 substantially in the middle.

In the cutter shown in figs. 5 to 8, the edge 72 is offset circumferentially relative to the edge 70 by a very small distance, so that these edges form a single chip having a central line of weakness. In practice, in a milling cutter intended for drilling holes in steel, the edge 72 should only be offset by about a quarter of the offset distance from the other teeth and preferably at most about 0.38 mm. The only deformed chip thus cut by the edges 70, 72 is very subject to breakage as soon as it encounters an obstacle. However, this single, weak chip is directed immediately into the wide groove 22, which eliminates the tendency of narrow chips to settle in the part of the groove which is between the shoulder 82 (fig. 8) and the side wall. 76 of the hole being drilled.

If the edge 72 is offset backwards with respect to the edge 70, so that each of these edges cuts an individual chip, it is then preferable that the part of the groove 22 associated with the edge 72 has the shape of a recess 84 (fig. 9) extending vertically over a distance substantially equal to the vertical dimension of the recesses 44, 50. Thus, when the edge 72 is sufficiently offset to cut a separate chip, the latter is directed by the recess 84 immediately in the wide groove 22 and does not tend to obstruct the recess 84.

When the cutter shown in fig. 9 is rotated and advanced in one piece, four separate chips are formed by the cutting edges 34, 36 and 70, 72. Using the cutter shown in Figs. 5 to 8, the edges 34, 36 each form a separate chip and, as explained above, the edges 70, 72 cut a single easily breakable chip. In either case, the chip formed by the edge 34 is directed immediately outward in the groove 22, and that formed by the edge 36 is also directed immediately upward and outward in said groove 22. Likewise, the single chip or the separate chips formed by the edges 70, 72 are directed from bottom to top in the edge 22.

However, immediately after the formation of the chips by the edges 34, 36, 70 and their routing in the groove 22, they come into frictional contact with the side wall 76 of the hole being drilled in the part. Since the chips, which have not been fractured, normally have an approximately helical configuration, when they come into contact with the side wall, the friction resistance thus created tends to prevent the helical chips from rotating with the strawberry. As a result, the chips

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immediately come into contact with the rear side wall 78 of the groove 22 (fig. 6) and, as described above, they are pushed upwards out of the groove without encountering any obstacle. Thus, because of the small circumferential dimension of the shoulder 82, when using the cutter shown in Figs. 5 to 8, the chips do not come into contact with said shoulder 82 and are therefore picked up by the rear side wall 80 of the groove 22. This is desirable because the tendency for the chips to get caught between the periphery of the cutter and the side wall 76 of the hole being drilled is substantially reduced. In addition, since the chips are narrow, they are less likely to scratch the wall of the hole being drilled as they go up along the grooves. In addition, narrow shavings are easily broken when they escape from the hole during drilling and therefore do not tend to wrap around the cutter and / or the shaft or mandrel and hinder the free passage of the chips formed later.

The presence of four cutting edges offset circumferentially and vertically, like those represented in FIGS. 5 to 8 and 9, has several other interesting advantages compared to the milling cutter shown in FIGS. 1 to 4. Firstly, all the cutting edges of these strawberries can be narrower than those shown on the strawberry of FIGS. 1 to 4, even if the two cutters have a core of the same thickness and grooves of the same depth. Thus, the chips formed by these edges can be even more easily removed and ejected from bottom to top via the grooves 22. Another advantage of the configurations shown in FIGS. 5 to 8 and 9, in which the part of the tooth corresponding to the depth of the groove consists of two cutting edges instead of one, lies in the fact that, if it is desired to make a milling cutter having an external diameter about 0.5 mm smaller than that of a conventional size cutter, just take a finished cutter of classic size and grind its periphery over a distance of 0.25 mm. Thus, the depth of the groove 22 is only reduced by 0.25 mm and is still sufficient to contain the width of the shavings cut by the other three cutting edges. Even with the cutter shown in fig. 1 to 4, it is obvious that the external diameter of the cutter can be reduced by grinding to obtain a cutter of special dimension, provided that the radial depth of the resulting groove is still of a width approximately equal to that of the widest chip.

Another advantage of the cutter, having at least two cutting edges both in the core and in the part of the tooth corresponding to the depth of the groove, lies in the fact that, when a metal chip is cut, it tends to deploy up to 10%. With the strawberries shown in fig. 5 to 8 and 9, the depth of the groove 22 is more than 10% greater than the width of the widest edge. Thus, the tendency of the chips which are deployed to get caught in the groove 22 or to close it is further attenuated. Even if the edges 70, 72 of the cutter shown in FIGS. 5 to 8 form a single chip, the latter has a central line of weakness and therefore breaks easily into small narrow chips.

With a cutter of the present invention, easy chip ejection and other advantages are obtained without this being at the expense of the mechanical strength of the cutter. This is due in particular to the fact that each tooth has at least three and preferably four or more cutting edges and that the depth of the groove may be substantially less than the width or the thickness of the core between the successive teeth. The mechanical resistance of an annular cutter having a grooved side wall is mainly determined by the thickness of the core. Thus, if the core of a particular cutter must have a predetermined minimum thickness, then the total thickness of the wall of a cutter of the invention may be less than that of a cutter of the prior art, being given that, thanks to the present invention, the depth of the groove can be less than the thickness of the core, while still being sufficient to contain the widest chip which is formed by any of the cutting edges. A thinner side wall is advantageous from a price point of view as well as for ensuring a narrow cutting path.

Another advantage of a cutter produced according to the invention is shown in FIG. 3. As pointed out above, the thickness of the core 26 near each tooth is greater than the depth of the groove 22. This results from the fact that the part of the tooth corresponding to the thickness of the core has at least two cutting edges, each of which has a width which preferably is substantially less than the depth of the groove. Thus, if the internal wall 28 of the groove inclines radially inwards and upwards in the immediate vicinity of its lower end and quite abruptly approximately up to the part designated by 62 in FIG. 3, the chip cut by the edge 38 immediately has a clearance relative to the groove. Also, when the internal face of the cutter is inclined, near its lower end, radially outward and upward, the core 26 has a minimum thickness near the upper end of the side wall of the cutter in the region designated by 86 in FIG. 3. This region 86 then becomes the critical region of the cutter with regard to its mechanical strength. Consequently, in the case of a conventional milling cutter of the prior art, in which the depth of an antlers is as great as the thickness of the core near the tooth of the milling cutter, the total thickness of the wall of said cutter should then be substantially larger if it were necessary to provide a groove of increasing depth from bottom to top and with a clearance around its internal face. It also appears that, in the case of a cutter according to the invention, it is possible to obtain a substantially greater clearance around the internal face of the cutter without it being necessary to increase the thickness of the wall of the latter. Greater clearance is also desirable to facilitate increasing the flow of coolant to the cutter teeth.

The presence of a relatively thick core and a relatively narrow groove in an annular cutter is also very important from the manufacturing point of view. In the case of a wall of a given thickness, when trying to grind a relatively deep groove in the side wall, small cracks or cracks have a strong tendency to form in the core and can be the cause of relatively short tool life. Relatively deep grooves also increase the tendency for cracking to form during heat treatment. However, if the groove is relatively narrow and the core is relatively thick, the latter can absorb substantially more heat and therefore significantly reduce the tendency to form such cracks during heat treatment and grinding of the grooves. A rough groove is also desirable from the point of view of manufacturing price. It can be machined or ground in less time and ensures a proportionately longer life of the tool.

Although not shown in the drawings, most hand mills require a pilot or a center drill. In practice, the bore 88 of the rod 14, which is intended to hold the pilot or the drill, must have at least one predetermined dimension. Thus the internal diameter of the cutter must be at least equal to the diameter of the pilot or the drill. Since the cutter has a core whose thickness is greater than the depth of the groove, it follows that with a hole intended for the pilot of a predetermined size, the external diameter of a cutter according to the invention may be less than the minimum external diameter of a cutter produced according to the prior art.

Another advantage, which results from the fact that the present cutter has a thicker core compared to that of the prior art, resides in the fact that it can be produced in two parts, a toothed part and a body part, nested axially in the region of the core and fixed together by threading, welding, etc. The thicker core allows such a telescopic connection without substantially affecting the mechanical strength of the cutter. A cutter built in two parts in this way obviously has an advantage from the manufacturing price point of view. The toothed part only needs to be made of steel

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expensive. In addition, when the teeth are worn, only the toothed part must be replaced and not the entire cutter.

A thicker core also makes it possible to produce a greater number of teeth around the periphery of said cutter, since it is able to withstand stronger push and torque. More teeth result in more cutting edges and faster cutting.

It has been determined that, from the point of view of the maximum mechanical resistance of the cutter relative to the ease of ejection of the chips, the thickness of the core between the successive teeth must be at least 55 to 60 % of the thickness of the annular wall of the cutter. In the case of strawberries of the type shown in FIGS. 5 to 8 and 9, when each tooth has four cutting edges, in the absence of special considerations, it is preferable to form the two internal edges substantially at the same width and the two external edges also at the same width. However, special considerations may impose other conditions; for example, if it is desirable to obtain a very smooth surface on the central cylindrical ingot, the innermost cutting edge 34 must be substantially narrower than the following edge 36 in the radial direction. In any case, the wider of these two edges must not have a width greater than the depth of the groove 22. Furthermore, if it is desirable to drill an extremely smooth hole in a part, then it is necessary that the outermost cutting edge 72 is much narrower than the following edge 70 in the radial direction. If it is desirable to drill both a smooth wall hole and to form a central core also with a smooth wall, the internal and external cutting edges must be narrower than the intermediate edges. In any case, when the cutter is intended for drilling holes in steel and has at least four cutting edges, the best results are normally obtained when the widest cutting edge has a width of not more than about 1.59 mm. . However, if one wishes

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greater rigidity, it is possible to considerably increase this width of the cutting edges, for example up to two or three times.

Also, although it is preferable to make the ridge between the 5 jagged faces 56, 58 so that it cuts the outermost cutting edge, for certain applications, the jagged faces can be ground so that the ridge cuts one of the other sharp edges. For example, if the cutter is to be used to drill a hole in two or more pieces that are stacked, the ridge for-10 placed between the two beaded faces must then be very close to the inner face of the side wall of the cutter . If the ridge or the high point of the cutter is close to the internal face of the side wall of the cutter, there is little difficulty in advancing the cutter through the two superimposed parts.

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The top point of the cutter can be shifted towards the internal cutting edge 34 without modifying the location of the edge 74. Since the bent face 56 tilts up and circumferentially, it follows that, if the shoulders 51, 54 have a sufficiently increased length, the crest 74 is at a distance above the ridge 34 instead of being below the latter. In this case, the edge 34 initiates the cut and enters the upper part before the ridge 74. Thus, if the edge 34 is kept at a very small width, the small lip which remains on the cut ingot does not prevent it no pe-2S enter from bottom to top in the bore of the cutter, so that the latter can sink freely into the underlying part.

Since a chip tends to expand slightly immediately after it has been cut, it is desirable to grind the surface 28 of the groove 22 so that the maximum radial depth of the latter is at the junction of the surfaces 28, 32. This minimizes the frictional resistance of the chip formed by the edge 38 against the internal wall of the groove.

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Claims (13)

643,168 2 1. Annular cutter to be bored, working from the front, which has a generally cylindrical annular side wall comprising several cutting teeth spaced circumferentially around its lower end and a means for mounting the cutter on a rotary drive element, several grooves extending upward around the periphery of the annular wall from its lower end, each groove having a circumferential dimension substantially greater than its radial dimension, each tooth being connected to the next adjacent tooth by a circumferential core along the inner face of the annular wall, the cores being radially juxtaposed with the grooves and having recesses at their lower ends which extend upwards and open at their upper end outwards in the radially adjacent groove, each groove having lateral walls circumferentially spaced and oriented front and rear s generally in the radial direction and a circumferential internal wall, the latter forming the radially external side of the core, milling cutter characterized in that each tooth (20) has a series of at least three cutting edges (34, 36, 38 ), oriented radially, consisting of a radially internal edge (34), a radially external edge (38) and at least one intermediate edge (36), the internal (34) and intermediate (36) edges of each tooth (20) being arranged with respect to each other so that each of them forms a separate chip when the cutter (10) is rotated and is advanced in a workpiece, in that the recesses (42 , 48) extend upwards from the internal (34) and intermediate (36) edges of each tooth, the internal edge (38) at least partially forming the lower end of the rear side wall of the adjacent groove (22), and in that each groove has a radial dimension which is not less than the radial dimension d e the widest of the internal edges (34) and intermediate (36), so that, when the cutter (10) is rotated and is advanced axially-ment in a metal part, the chips formed by the internal edges (34 ) and intermediate (36) on the core (26) of the side wall of the cutter are directed upwards first in their respective recess (42,48), then upwards of this respective recess in the groove radially adjacent (22). 2. Milling cutter according to claim 1, characterized in that the cutting edges (34,36, 38) of each tooth (20) are offset circumferentially, so that the radially outer end of the inner edge (34) is offset forward in the direction of rotation of the cutter (10) relative to the radially inner end of the intermediate edge (36), and the radially outer end of the intermediate edge (36) is offset towards the 'before the radially inner end of the outer edge (38). 3. Milling cutter according to claim 1, characterized in that the recesses comprise a first recess (42) extending upwards from the internal edge (34) and a second recess (48) extending upwards from of the intermediate edge (36), but not beyond the upper end of the first hollow (42). 4. Milling cutter according to claim 1, characterized in that the thickness of the core (26) exceeds half the thickness of the annular wall at its lower end. 5. Milling cutter according to claim 1, characterized in that the radial dimensions of the internal (34), intermediate (36) and external (38) edges are the same. 6. Milling cutter according to claim 1, characterized in that the radially internal cutting edge (34) of each tooth (20) is narrower than the remaining edges (36, 38). 7. Milling cutter according to claim 1, characterized in that the external cutting edge (38) is narrower than the other edges (34, 36). 8. Milling cutter according to claim 1, characterized in that the two radially innermost cutting edges (34, 36) have a combined radial dimension which is not greater than the thickness of the core (26) near the edges. 9. Milling cutter according to claim 1, characterized in that each tooth (20) has four cutting edges oriented radially (34, 36, 70, 72), the two outermost edges (70, 72) forming the lower end of the rear side wall (80) of the adjacent groove (22). 10. Milling cutter according to claim 9, characterized in that the pa- 5 rear lateral king (80) of each groove (22) forms a continuous and regular helix extending upwards from the two outermost edges (70, 72) over the entire axial length of the side wall of the cutter ( 10). 11. Milling cutter according to claim 9, characterized in that the io four cutting edges (34, 36, 70, 72) are circumferentially offset progressively in the direction of rotation of the radially external edge (72) to the radially internal edge (34). 12. Milling cutter according to claim 11, characterized in that the radially outermost edge (72) is offset from 15 the next edge (70) in the radial direction, so that the two outermost edges form a single chip. 13. Milling cutter according to claim 11, characterized in that the two outermost edges (70, 72) are sufficiently offset so that they each form a separate chip.