MINIATURE INTERNAL BORING TOOL

Abstract

A miniature internal boring tool including two to four shank flat surfaces and two to four integrally formed teeth. The outermost points of cutting edges of the teeth define an outer cutting diameter (OD) fulfilling the condition: 2 mm<OD<9 mm.

Claims

1. A miniature internal boring tool comprising: a shank portion; a cutting portion extending from the shank portion; and a central axis extending through the center of the shank portion and cutting portion; the central axis defining: a cutting direction; a forward direction from the shank portion towards the cutting portion; a rearward direction opposite to the forward direction; an outward direction extending perpendicular to, and outward from, the central axis; and an inward direction opposite to the outward direction; the shank portion comprising: a rear end; and a peripheral shank surface extending from the rear end to the cutting portion; the peripheral shank surface comprising: two to four shank flat surfaces; and two to four shank curved surfaces; the shank flat surfaces and the shank curved surfaces alternating about the central axis; the cutting portion comprising: a neck portion extending from the shank portion to the cutting portion; a gashed portion extending forward from the neck portion; a front end; and an imaginary plane perpendicular to the central axis and located at the front end; the gashed portion comprising: two to four integrally formed and angularly spaced apart teeth extending further in the outward direction than the neck portion; and a plurality of gashes; each tooth comprising: a rake surface; a relief surface; a cutting edge extending along an intersection of the rake surface and relief surface; and the relief surface comprising: a forwardmost relief sub-surface; and a rearwardmost relief sub-surface; the cutting edge comprising: a forwardmost cutting sub-edge extending along the intersection of the rake surface and forwardmost relief sub-surface; a rearwardmost cutting sub-edge extending along the intersection of the rake surface and rearwardmost relief sub-surface; and a nose cutting sub-edge connecting the forwardmost cutting sub-edge and the rearwardmost cutting sub-edge; a transition corner is formed between the rake surface of at least one of the teeth and the relief surface of the adjacent tooth to said at least one of the teeth, said adjacent tooth being located further in the cutting direction from said rake surface; wherein: outermost points of the cutting edges in the outer direction define an outer cutting diameter (O.sub.D) fulfilling the condition: 2 mm<O.sub.D<9 mm.

2. The miniature internal boring tool according to claim 1, wherein in a view perpendicular to the rake surface of one of the teeth, the forwardmost cutting sub-edge of that tooth can extends in the forward direction and subtends an external attack angle A.sub.E with the imaginary plane PI, fulfilling the condition: 4<A.sub.E<16.

3. The miniature internal boring tool according to claim 2, fulfilling the condition: 6<A.sub.E<12.

4. The miniature internal boring tool according to claim 3, fulfilling the condition: 6<A.sub.E<10.

5. The miniature internal boring tool according to claim 1, further fulfilling the condition: 2 mm<O.sub.D<6 mm.

6. The miniature internal boring tool according to claim 5, further fulfilling the condition: 2.5 mm<O.sub.D<4 mm.

7. The miniature internal boring tool according to claim 1, comprising exactly three shank flat surfaces and exactly three teeth and the outer cutting diameter (O.sub.D) fulfills the condition: 2 mm<O.sub.D<6 mm.

8. The miniature internal boring tool according to claim 1, wherein the total number of said gashes corresponds exactly to the total number of said teeth.

9. The miniature internal boring tool according to claim 1, wherein one of the plurality of gashes has a gash length L.sub.G parallel to central axis, and the neck has a neck length L.sub.N parallel to central axis, the gash length L.sub.G fulfilling the condition L.sub.G<0.35 L.sub.N.

10. The miniature internal boring tool according to claim 9, wherein the gash length L.sub.G fulfills the condition L.sub.G<0.25 L.sub.N.

11. The miniature internal boring tool according to claim 9, wherein the gash length L.sub.G fulfills the condition L.sub.G<0.22 L.sub.N.

12. The miniature internal boring tool according to claim 1, wherein the rake surface of one of the teeth comprises: a front rake sub-surface extending between the forwardmost cutting sub-edge, the rearwardmost cutting sub-edge and the nose cutting sub-edge; a concave rake sub-surface, extending from and further in the inward direction from the front rake sub-surface; and a rear rake sub-surface extending from and further in the inward direction from the concave rake sub-surface; wherein, in a view along the central axis in the rearward direction, the rear rake sub-surface extends in a basic straight path to the transition corner of the tooth adjacent thereto in the cutting direction.

13. The miniature internal boring tool according to claim 12, wherein, in a view along the central axis in the rearward direction, the transition corner is a sharp corner.

14. The miniature internal boring tool according to claim 1, wherein, in a view along the central axis in the rearward direction, the transition corner is a sharp corner.

15. The miniature internal boring tool according to claim 1, comprising exactly three shank flat surfaces and exactly three teeth, wherein in a view along the central axis in the rearward direction, at the front end coinciding with the imaginary plane, a void area A.sub.V defined between two adjacent cutting edges and bounded by a circular segment SC defined by outer cutting diameter Op fulfills the condition: 0.10 O.sub.D<A.sub.V<0.25 O.sub.D.

16. The miniature internal boring tool according to claim 15, further fulfilling the condition: 0.12 O.sub.D<A.sub.V<0.22 O.sub.D.

17. The miniature internal boring tool according to claim 16, further fulfilling the condition: 0.14 O.sub.D<A.sub.V<0.20 O.sub.D.

18. The miniature internal boring tool according to claim 1, wherein the shank flat surfaces extend until the rear end.

19. The miniature internal boring tool according to claim 1, wherein one of each shank flat surface and an axially aligned one of each rake surface of one of the teeth forms a pair and said pair extends at a right angle to each other.

20. The miniature internal boring tool according to claim 1, wherein the tool is 120 rotationally symmetric.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] For a better understanding of the subject matter of the present application, and to show how the same may be carried out in practice, reference will now be made to the accompanying drawings, in which:

[0044] FIG. 1 is a perspective view of a tool according of the present invention;

[0045] FIG. 2 is a rear end view, along a central axis A.sub.C, of the tool in FIG. 1;

[0046] FIG. 3 is a side view of the tool in FIG. 1, in a view perpendicular to a rake surface of a left tooth;

[0047] FIG. 4 is side view of the tool, similar to FIG. 3, except with the tool rotated 90 degrees such that the cutting edge of the left tooth in FIG. 3 is now centrally located;

[0048] FIG. 5 is an identical view to FIG. 3;

[0049] FIG. 6 is an identical view to FIG. 4;

[0050] FIG. 7 is a side view of a prior art tool, in a view similar to FIG. 3, specifically in a view perpendicular to the rake surface of the left tooth;

[0051] FIG. 8 is a side view of the prior art tool in FIG. 7, in a view similar to FIG. 4, specifically with the tool rotated 90 degrees such that the cutting edge of the left tooth in FIG. 7 is now centrally located;

[0052] FIG. 9 is a front end view (also called a view along the central axis in the rearward direction), along the central axis A.sub.C, of the tool in FIG. 1, with a dashed line schematically indicating an internal bore of a workpiece within which the cutting portion of the tool is accommodated, and a hashed section schematically indicating a bore area A.sub.B, perpendicular to a central axis A.sub.C and at an imaginary plane at the front end, between the cutting portion and the internal bore;

[0053] FIG. 10 is a front end view, along a central axis A.sub.C2, of the prior art tool in FIG. 7, with a similar dashed line and hashed section to that described in connection with FIG. 9; and

[0054] FIG. 11 is an identical view to FIG. 9, except that the dashed line in this figure indicates an outer cutting diameter and the hashed section schematically indicates a void area A.sub.V, along the central axis A.sub.C and at an imaginary plane at the front end, between the cutting portion and bounded by a circular segment SC defined by the outer cutting diameter O.sub.D.

DETAILED DESCRIPTION

[0055] Referring to FIGS. 1 to 4, there is shown a miniature internal boring tool 10 comprising a shank portion 12 and a cutting portion 14.

[0056] A central axis A.sub.C extends through the center of the shank portion 12 and cutting portion 14.

[0057] The central axis A.sub.C defines a cutting direction D.sub.C, a forward direction D.sub.F, a rearward direction D.sub.R opposite to the forward direction D.sub.F, an outward direction D.sub.O (shown best in FIG. 2, the extra arrows in FIGS. 3 and 4 are to exemplify that the outward direction D.sub.O is not a single direction but all outward directions from the central axis A.sub.C) extending perpendicular to, and outward from, the central axis A.sub.C, and an inward direction D.sub.1 (shown best in FIG. 2, the extra arrows in FIGS. 3 and 4 are to exemplify that the inward direction D.sub.1 is not a single direction but all inward directions to the central axis A.sub.C) opposite to the outward direction D.sub.O.

[0058] The shank portion 12 comprises a rear end 16 and a peripheral shank surface 18 extending from the rear end 16 to the cutting portion 14.

[0059] The peripheral shank surface 18 comprises three shank flat surfaces 20 (designated individually as 20a, 20b, 20c). For succinctness, elements below may be referred to below with the general designation, for example 20 for shank flat surfaces, instead of their individual designations 20a, 20b, 20c). The peripheral shank surface 18 also comprises three (preferably cylindrically-shaped) shank curved surfaces 22 (individually designated 22a, 22b, 22c).

[0060] While it appears that there are six shank flat surfaces 20, it will be understood that coolant slots 24 (individually designated 24a, 24b, 24c) formed in the shank portion 12 are optional and therefore the above indicated designated shank flat surfaces (20a, 20b, 20c) are pairs of shank flat sub-surfaces which are considered a single shank flat surface. In particular, they may be functionally identical (e.g. a screw from a tool holder, both not shown, is intended to simultaneously contact both shank flat sub-surfaces of a single pair, for example, the pair of shank flat sub-surfaces both designated 20a).

[0061] The cutting portion 14 comprises a neck portion 26, a gashed portion 28, a front end 29 and an imaginary plane PI perpendicular to the central axis A.sub.C and located at the front end 29.

[0062] The neck portion 26 has a basic cylindrical cross section (see, e.g., FIG. 2) and a neck length L.sub.N (FIG. 6), which in this very example is 8.4 mm. It should be noted, however, that the general structure, geometry and dimensional ratios of this very embodiment is not limited to the exact dimensions mentioned in the discussion of the figures but equally apply to tools having dimensions within the ranges referred to herein above.

[0063] The neck portion cross section has a diameter , which in this example is 2.1 mm.

[0064] The gashed portion 28 comprises three integrally formed teeth 30 (individually designated 30a, 30b, 30c) and a three planar gashes 32 (individually designated 32a, 32b, 32c).

[0065] The tool 10 has, in this example, three teeth 30, and therefore is 120 rotationally symmetric (as the number of teeth divided by 360 is 120) about the central axis A.sub.C. As the teeth 30 and the other elements are identical, the description above and below may refer to a single sub-element on one and it should be understood that this description applies to all the other identical elements. It should also be understood, that a tool according to the present invention could have minor non-identical differences such as the gashes being slightly different length without any change in efficiency. It should further be understood that the present invention does not require all elements to be identical and that this is only a preferred configuration.

[0066] Each tooth 30 comprises a rake surface 34, a relief surface 36, and a cutting edge 38.

[0067] Referring also to FIG. 11, the rake surface 34 can comprise: a front rake sub-surface 34a, a rear rake sub-surface 34b and a concave rake sub-surface 34c.

[0068] The relief surface 36 comprises a forwardmost relief sub-surface 36a and a rearwardmost relief sub-surface 36b.

[0069] A chip evacuation angle in this exemplary embodiment is 117.

[0070] In this example, as best seen in FIG. 2, the forwardmost relief sub-surface 36a has two facets, namely a first relief facet 36al connected to the cutting edge 38, and a second relief facet 36a2 extending from the first relief facet 36a1.

[0071] Additionally, in FIG. 11, a sharp transition corner is designated 40 and is shown located at an intersection of one of the rake surfaces 34 and one of the relief surfaces 36 located further in the cutting direction D.sub.C than said rake surface 34. More precisely, the transition corner 40 is located at the intersection of the rear rake sub-surface 34b and the second relief facet 36a2.

[0072] Reverting to FIGS. 3 and 4, the cutting edge 38 comprises a forwardmost cutting sub-edge 38a, a rearwardmost cutting sub-edge 38b and a nose cutting sub-edge 38c.

[0073] In the present example, and in preferred embodiments, the nose cutting sub-edge 38c of all of the teeth 30 constitutes both the outermost points and forwardmost points of the tool 10. Therefore, for example, the imaginary plane PI is defined by the nose cutting sub-edges 38c, as they include the forwardmost points of the tool 10. Another example is that the nose cutting sub-edges 38c define an outer cutting diameter O.sub.D (FIG. 2), as they include the outermost points of the tool 10. In this example the outer cutting diameter (O.sub.D) is 2.7 mm.

[0074] Drawing particular attention to FIGS. 5 and 6, the forwardmost cutting sub-edge 38a subtends an external attack angle A.sub.E with the imaginary plane PI, which in this example is 8.

[0075] The rearwardmost cutting sub-edge 38b of the tooth subtends an external attack angle A.sub.R with the forward direction D.sub.F, which in this example is 20.

[0076] The cutting portion 14 has a cutting portion length L.sub.C, which in this example is 10 mm.

[0077] Each gash 32 has a gash length L.sub.G, which is defined as extending from a rearmost gash edge 32a to the forwardmost point of the tooth 30 with which the gash 32 is associated (in this case the forwardmost point coinciding with the imaginary plane PI or alternatively the nose cutting sub-edges 38c which define the imaginary plane PI). In this example the gash length L.sub.G is 1.6 mm.

[0078] The rearwardmost cutting sub-edge 38b has a rear edge length L.sub.R, which in this example is 0.6 mm.

[0079] The shank flat surfaces 20 extend until the rear end 16 and have a shank flat surface length L.sub.F, which in this example is 17.5 mm.

[0080] The shank flat surfaces 20 can have a shank flat surface width WF, which in this example is 2.6 mm.

[0081] The shank portion 12 comprises a cylindrical shank sub-portion 42 between the shank flat surfaces 20 and the neck portion 26, and has an overall shank length L.sub.S, which in this example is 21 mm.

[0082] As shown in FIG. 2, the coolant slots 24 are axially aligned with a corresponding cutting edge 38. The coolant slots 24 breach the shank portion 12 to extend into the neck portion.

[0083] Each shank flat surface 20 is axially aligned with one of each rake surfaces 34 of one of the teeth, which forms a pair.

[0084] As shown in FIG. 2, to simply give an example, the shank flat surface designated 20a is paired with one of the rake surfaces arbitrarily given a designation of 34d for exemplary purposes, thereby creating one such pair. As shown the shank flat surface 20a extends at a right angle to the rake surface 34d, specifically the front rake sub-surface (arbitrarily given a designation of 34e) of the rake surface 34d.

[0085] As shown in FIG. 11, the rear rake sub-surface 34b extends in a basic straight path to the transition corner 40.

[0086] Referring now to FIGS. 5 to 8 there will be a comparison with some notable differences between the prior art tool 110 in FIGS. 7 and 8 with the example tool 10 of the present invention.

[0087] In the prior art tool 110, the axis A.sub.C2 does not extend through the center of both the shank portion 112 and the cutting portion 114.

[0088] There is a single shank flat surface 120 and a single cylindrically-shaped shank curved surface 122.

[0089] The shank curved surface 122 extends flush with a curved surface 127 of a neck portion 126, the significance of which is explained above.

[0090] The cutting portion 114 has a cutting portion length L.sub.C2, which in this example is 10.3 mm.

[0091] The neck portion 126 has a neck length L.sub.N2, which in this example is 6.5 mm. It will be understood that this is a comparative length for the cylindrical cross section part of the cutting portion 114. Alternatively, if including part of the gash 132, the neck portion 126 could be considered to have an alternative neck length L.sub.N3, which in this example is 8.1 mm. Regardless, it will be understood that the tool 10 does not have a comparative gash portion arbitrarily designated 132d which is upwardly slanted and removes further material from the cylindrical cross sectional part of the neck portion 126.

[0092] The neck portion 126 at a basically cylindrical part thereof, has a diameter 2, which in this example is 2.3-2.4 mm, depending on the direction of measurement.

[0093] Regardless of the direction, it should be understood that due to the inclusion of multiple teeth in the tool 10, the design resulted in a smaller diameter , which was a concern for stability but that was found to provide suitable performance.

[0094] More notably, the gashes 132 are significantly longer, with the comparative gash length L.sub.G2 being 3.8 mm. Or, alternatively, even with an alternative gash length L.sub.G3 being larger at a length of 2.2 mm.

[0095] Similarly, the rearwardmost cutting sub-edge 138b has a rear edge length L.sub.R2, which is also significantly longer, equaling 0.96 mm.

[0096] The significance of the numerical comparisons brought above is that even with significantly smaller gashes and longer neck portions with a cylindrical cross section, it was surprisingly found that there was sufficient chip evacuation space and sufficient rigidity for the tool according to the present invention.

[0097] Finally, it is noted that the external attack angle A.sub.E2 is 20.

[0098] Despite the differences shown above, it should be noted that the tool 10 successfully provides similar material removal performance to the prior art tool 110.

[0099] To elaborate on the importance of chip evacuation, attention is now drawn to FIGS. 9 and 10, respectively schematically showing the cutting portions of the tool 10 and the prior art tool 110 within an exemplary workpiece's bore B having an exemplary bore diameter 3 of 2.8 mm.

[0100] Hereinbelow, some comparative sizes will be discussed.

[0101] Regarding the tool 10, a forwardmost cutting sub-edge measurement M.sub.F, measured from the nose cutting sub-edge 38c of an operative cutting edge 38 contacting the bore B to the start of the concave rake sub-surface 34c, is, in this example, 0.5 mm. A transition measurement MT, measured from said nose cutting sub-edge 38c to the transition corner 40, is, in this example, 1.2 mm. The chip evacuation space shown schematically as a bore area A.sub.B, is from one cutting edge 38 to another in the cutting direction and is, in this example, approximately 17% of the area of the imaginary plane PI within the bore B.

[0102] By comparison, prior art tool 110 has relative comparative dimensions, as follows: a forwardmost cutting sub-edge measurement M.sub.F2 is 1.15 mm. A basically comparative transition measurement M.sub.T2, even though there is no additional cutting edge, is 1.3 mm. The chip evacuation space shown schematically as a bore area A.sub.B2, is approximately 49% of the area of the imaginary plane PI within the bore B.

[0103] Thus, even with tremendously reduced chip evacuation space and a seemingly smaller cutting edge or rake surface, the tool 10 still provides similar, and surprisingly successful (given the smaller chip evacuation space), material removal performance to the prior art tool 110, while at the same time maintaining sufficient rigidity.

[0104] It will be understood that given the incredibly small difference between the tool outer diameter O.sub.D and the bore B, that this is no simple matter.

[0105] The above dimensions will now be similarly discussed independent of a reference to a workpiece or bore B.

[0106] Referring to FIG. 11 the dashed line refers to the outer cutting diameter Op and the hashed section schematically indicates a void area A.sub.V, perpendicular to a central axis A.sub.C and at an imaginary plane at the front end, between the cutting portion and bounded by a circular segment SC defined by the outer cutting diameter O.sub.D.

[0107] Regarding the tool 10, a forwardmost cutting sub-edge measurement M.sub.F, measured from the nose cutting sub-edge 38c of an operative cutting edge 38 contacting the bore B to the start of the concave rake sub-surface 34c, is 0.5 mm. A transition measurement MT, measured from said nose cutting sub-edge 38c to the transition corner 40, is 1.2 mm. The chip evacuation space shown schematically as a bore area A.sub.B, is from one cutting edge 38 to another in the cutting direction and is approximately 17% of the area of the imaginary plane PI within the bore B.

[0108] The description above includes an exemplary embodiment which does not exclude non-exemplified embodiments from the claim scope of the present application.