HOLE FORMING TOOL WITH AT LEAST ONE ROTATABLE CUTTING MEMBER
The invention relates to hole forming tools suitable for use in subterranean drilling operations, operable with two non-parallel rotational motions for forming a hole of substantially circular cross section in a material, the tool comprising a rotatable drill body (17) having a proximal end (19) for attachment to a drive mechanism and a distal end (21) on which is disposed at least one rotatable cutting member (23), wherein the or each rotatable cutting member (23) independently extends away from said distal end (21); the or each rotatable cutting member (23) independently being substantially concentric with and supported by a cantilever shaft (35); wherein on the or each rotatable cutting member (23) is disposed at least one cutting structure (24), the or each cutting structure (24) independently having a cutting face with a continuous cutting edge which is substantially concentric with the axis of rotation of said rotatable cutting member (23).
The present invention relates to a tool for forming a hole. More particularly, the invention relates to a tool operable with two non-parallel rotational motions for forming a hole of substantially circular cross section in a material.
Hole-making, hole forming or drilling by the removal of material is often an expensive and time-consuming process due to the wear of cutting edges and the necessity for replacement of the hole forming tool so as to maintain productivity and or the quality of the formed hole. Despite substantial improvements in the geometry and construction of drilling tools and the hard materials comprising the cutting edges, there is an ever-increasing desire to further improve such tools so as to provide for longer tool life whilst maintaining productivity and or the quality of the hole. One requirement of hole forming tools is that they possess sufficient strength and toughness so as to withstand high forces and often a dynamic load component arising from drilling vibrations or heterogeneity within the material being cut.
It is known in the art that prolonged continuous contact between a cutting edge and the material being cut is deleterious in terms of cutting edge wear and several approaches have been developed to address this issue. For rotationally symmetric cutting tools, one such approach is to permit the tool to rotate freely or in a regulated manner about its own axis, e.g. as disclosed in US 2014/0186127 A1. Although such self-propelled rotary turning tools have been known in the art for several decades, industrial use is rare. In the field of subterranean drilling, tools incorporating cutting edges permitted to rotate about an axis substantially perpendicular to the axis of primary rotation were a popular approach about one century ago in the form of ‘disc cutters’. With reference to
Certain subterranean drill bits comprise a plurality of cylindrical polycrystalline diamond cutters, commonly ranging in diameter from ½-¾ inch (12.7-19 millimetres), and arranged on a plurality of blades on the drill body. Such tools are generally referred to in the art as “shear bits” or “drag bits”, as exemplified in U.S. Pat. No. 8,327,956, US 2010/0089648, US 2014/0097028, WO 2011/090618A1 and WO 2014/028152. U.S. Pat. No. 4,511,006 discloses a shear bit for mining as shown in
Another class of drilling tools, known in the field as “roller cones” (IPC E21B10/08), exert a crushing action on the material to be removed. With reference to
WO 1999/18326 describes a drill bit with rolling ‘disc cutters’. WO 1999/11900 describes a drill employing multiple discs disposed on rotatable members. CN 102747960, WO 2015/178908 and WO 1985/02223 describe other hybrid drill bits of similar function. Disc-like rolling structures appear not to have been widely successful.
All drilling tools intended for subterranean drilling applications have a threaded element 8 for attachment to the drive mechanism, nozzles 15 for delivery of cutting fluid and hard, abrasion resistant, non-cutting elements 14 disposed on regions of the drill body which are otherwise vulnerable to excessive wear.
As a result of the limitations of the prior art, there is a need for an improved hole forming tool so as to provide improved tool life, drilling productivity and/or improved hole quality, especially during subterranean drilling operations.
SUMMARYThe present invention provides hole forming tools suitable for subterranean drilling and is particularly defined in the appended claim which are incorporated into this description by reference and for the purposes of economy of presentation are not reproduced verbatim in the description.
The present invention will now be described with reference to the accompanying drawings,
In the drawings:
In one aspect, embodiments disclosed herein relate to hole forming tools with defined cutting structures which are rotatable and therefore have greater resistance to wear; said cutting structures being disposed to shear rather than crush the material to be cut. The cutting structures extend from the distal end of the drill body which is the working face of the hole forming tool and are disposed on, preferably attached rigidly, to rotatable cutting members which in turn are supported on and permitted to rotate on bearings disposed on cantilever shafts. Each cantilever shaft extends from the tool body. While it has long been known, particularly in the art of metal cutting lathe tooling, that cutting elements of a larger diameter are inherently more robust and resistant to impact loading than those of a smaller diameter, prior art drills which permit cutting structure rotation fail to combine sizeable cutting structures with robust, mechanically sound bearing arrangements and those prior art drills that do provide for sizeable rotatable cutting elements, fail to provide a robust and stiff cutting structure which is resistant to bending, breakage and or vibration. The hole forming tools of the invention address these shortcomings and additionally provide for the incorporation of several cutting structures on a compact but rigid rotatable cutting member and the exposure of each cutting structure to a share of the applied load so as to limit the maximum load applied to any one cutting structure, thereby significantly reducing the likelihood of fracture in use.
Referring to the drawings,
So as to provide a sufficiently robust design with sufficient space to permit the evacuation of cuttings, it may be preferable to incorporate reliefs 25 within the drill body elements. It will also be appreciated that it is desirable to have a degree of overlap between any inner arrangement of cutting structures and any outer arrangement of cutting structures—such overlap being apparent when the cutting edges of inner and outer cutting structures are rotationally projected about the axis of the drill body onto a radial plane of the drill body. Advantageously therefore, the angular position of the drill body elements 22 supporting the inner and outer rotatable cutting members 24 are preferably staggered. Where an inner and outer arrangement of drill body elements is adopted, the drill body elements and hence cutting structures 24 are preferably positioned at equal angular intervals or alternatively positioned at unequal angular intervals. Without being bound by theory, this positioning of the cutting structures 24 is considered to be helpful in counteracting regenerative vibration. A similar effect may also be achieved in embodiments of the present invention by providing differing angles of inclination of the cantilever shafts relative to radials of the drill body when viewed in a transverse plane of the drill body.
In addition to the distinct arrangement of inner and outer rotatable cutting members 23 or more generally, distinct groups of rotatable cutting members 23 positioned along substantially distinct circles of rotation about the drill body axis, in an alternative embodiment, each rotatable cutting member is positioned on a unique circle of rotation about the drill body axis. It will be noted that any arrangement of rotatable cutting members 23 and their cutting structures 24 must provide for a balanced hole forming tool such that any forces acting normal to the axis of rotation of the drill body 17 during use are minimal. This is provided by the invention.
Flutes 18 are preferably located adjacent the outermost drill body elements 22 such that cuttings exiting the associated cutting structures 24 have free passage into the flutes 18. The flutes 18 also reduce the area of contact between the drill body 17 and the hole being formed and thus serve to reduce frictional heating and wear. Preferably, innermost drill body elements 22 and associated rotatable cutting members 23 and cutting structures 24 lie at an angular position on the drill body which provides for easy flow of cuttings into the flutes 18.
In other preferred embodiments of the current invention, rotatable cutting members 23 with cutting structures 24 disposed thereon and with associated supporting cantilever shafts, may only be disposed on certain annular or segmental regions of the working face (distal end) of the hole forming tool, with remaining regions of the working face provided with non-rotatable fixed cutting structures.
Referring to
In the preferred embodiment shown in
Referring to
As shown in
While the embodiments illustrated include either two cutting structures 24 disposed on each rotatable cutting member 23 as shown in
With reference to
Referring to
Aspects of embodiments of the present invention depicted in one Figure may be interchangeable or combined with aspects of embodiments depicted in other Figures. Features on one cutting structure or on one location of a rotatable cutting member may be applied to other cutting structures and other locations of rotatable cutting members. Aspects illustrated in
Embodiments of the present invention may differ also at least in terms of the angles of inclination of, the position of, and the construction of the cantilever shafts relative to the drill body axis; the configuration of the rotatable cutting members and their respective cutting structures; the cutting edge and clearance face geometry of the cutting structures; the geometry of the drill body and drill body elements; bearings, sealing elements and the construction of pressure equilibration devices and any methods used to realise articles in accordance with the present disclosure. Features such as gage pads and flushing nozzles, as are used on prior art shear drills and roller cone drills are preferably also incorporated in the hole forming tools of the invention.
With regard to the direction of rotation of a rotatable cutting member;
In
In turn, the torque on each cutting structure will depend in part on the un-deformed cross-sectional area of cut to which that cutting structure is exposed and hence, the drill translation rate and the degree of overlap between adjacent cutting structures. The degree of overlap is illustrated in
There is a necessary minimum clearance angle γ_min, required on each cutting structure so as to avoid contact between it and the just-formed surface of the hole being drilled. Such clearance should not be excessively large so as to compromise the strength of the cutting edge. Generally, the cutting structures have substantially conical clearance surfaces. Such conical forms incur virtually no compromise in terms of performance, compared to more complex forms constructed for example, by using the helical trajectory or approximation thereof, of a point of interest P on the cutting edge as a generatrix about the axis of the rotatable cutting member.
With reference to
-
- Vectors through points P1 and P2, each parallel to the axis A (note in
FIG. 10b , all lines parallel to the axis A are marked “=”) and, - The tangents, Tn1 and Tn2, to the helices H1 and H2, passing through the points of interest on the circle C, said helices defined by:
- The diameter of the respective circle of rotation through each point of interest P, about the axis of rotation of the drill body; the projection of said circles onto the XY plane shown as Cy1 and Cy2 in
FIG. 10b ; and - The translation per revolution of the drill body.
- The diameter of the respective circle of rotation through each point of interest P, about the axis of rotation of the drill body; the projection of said circles onto the XY plane shown as Cy1 and Cy2 in
- Vectors through points P1 and P2, each parallel to the axis A (note in
Depending on the position and inclination of the cutting structure and absent any overlapping cutting structures, the minimum necessary clearance angle γ_min is determined at one or other of the positions P1 or P2. In
Where one or more adjacent cutting structures are positioned such that points equivalent to either or both P1 or P2 will not engage the material to be drilled—in effect being shielded by one or more adjacent overlapping cutting structures—the minimum necessary clearance angle γ_min should be determined at one or other of the points on the cutting edge denoting the extremities of the engagement region on that edge. By the term “engagement region” is meant that part of the cutting edge of a cutting structure which at any given instant during use of the hole forming tool engages the material in which a hole is to be formed. Identical cutting structures disposed on two or more identically sized rotatable cutting members which are positioned in an identical manner on the drill body but for the angular position of their respective reference radials, are not considered to ‘overlap’ in accordance with the use of the term in the present disclosure. In such cases, the engagement region of each cutting structure is practically identical to an arrangement where only one such rotatable cutting member is disposed on the drill body. The term ‘overlap’ relates here to adjacent cutting structures, each of which shields a portion of the other so as to effectively reduce the engagement region on one or both cutting edges. By nature of being rotatable, every part of the cutting edge of a cutting structure in accordance with the present invention is for some period within an engagement region.
The cutting structure and any supporting region of the rotatable cutting member has a finite thickness T along the axis of the rotatable cutting member. The minimum necessary clearance angle γ_min determined at the cutting face may not in all cases be sufficient to ensure clearance at the rear face of that cutting structure (the rear face being that which opposes the cutting face and positioned at a distance T from the cutting face). The methodology noted above for both the cutting face and the rear face indicates at which location the interference angle is greatest (in a positive sense). The face at which the maximum interference angle occurs is the determinant of the minimum necessary clearance angle.
It is, in some cases, possible to provide a conical surface whose apex angle is less than twice the maximum interference angle at the rear face, yet still maintain clearance on the cutting structure during use.
The conical or similar form of the clearance face of a cutting structure, being concentric with the axis of rotation of the rotatable cutting member, ensures the clearance angle relative to the axis of the rotatable cutting member is constant at all points on the circumference of that cutting structure. With respect to the presentation of the cutting structure to the material in which a hole is to be formed, the effective clearance angle varies along the engagement region of the cutting edge. By way of illustration and with reference to
More generally, determination of the maximum effective clearance angle, hereafter denoted γeff max, employs the minimum interference angle over the entire engagement region of the cutting edge, rather than α2 as in the simplified case above. Therefore (and omitting for the present, the possible refinement noted above concerning a maximum interference angle at the rear face of the cutting structure), γeff max is the difference between the maximum and the minimum angles of interference (ϕmax and ϕmin respectively); i.e., γeff max=ϕmax−ϕmin. Generally, ϕmin is a negative quantity in accordance the convention adopted in this disclosure.
Where there is a multiple m of engagement regions on a cutting structure, m being a whole number greater than one, γeff max within each engagement region is determined using the maximum of the m minimum necessary clearance angles, each of the m minimum necessary clearance angles is determined for each engagement region. Part of the cutting edge comprising one instantaneous engagement region at a first position relative to the drill body will at other times comprise part of another instantaneous engagement region at a second position relative to the drill body. γeff max within an engagement region is determined using the minimum angle of interference for that engagement region.
Conditions 1 and 2 and the Equations 1-13 hereinbelow summarise the considerations outlined above with regard to determining γeff max. These equations define the maximum effective clearance angle γeff max on an engagement region of a cutting structure which is provided with a minimum necessary clearance angle γ_min. The ‘Max’ terms in Equations 1 and 2 represent the minimum necessary clearance angle. The ‘Min’ terms in Equations 1 and 2 represent the minimum (most negative) angle of interference. Each of these angular quantities are independently dependent on the parameters α1, α2, d, T, Rb, rc and also the hole forming tool translation per revolution f which determines the pitch of the helical path followed by each point on the engagement region of the cutting edge of interest.
The position of each point of interest on an engagement region is given with respect to the rotatable cutting member by the coordinates λ and t. λ lies in the interval [λ1, λ2], where λ1 and λ2 are cutting face angular coordinates denoting the extremities of the engagement region of interest. The ‘Min’ terms in Equations 1 and 2 are evaluated over the interval [λ1, λ2]. Where there is more than one engagement region on a cutting structure, the ‘Max’ terms are evaluated over each angular interval relating to each engagement region on the cutting structure of interest. That is to say, the ‘Max’ terms are evaluated over the entire set Γ, where Γ comprises at least one sub-set, each sub-set being the angular interval [λ1, λ2] for each engagement region on the cutting structure of interest. The determination of the coordinates λ1 and λ2 is described below; but by way of illustration, where for an isolated cutting structure, the hole forming tool translation per revolution f is negligible in magnitude relative to the cutting structure radius rc, λ1 and λ2 are about 0° and 180°, respectively.
In
The parameter t is either 0 or T. The quantity (d−t) is referenced from the point of intersection I of the axis of the rotatable cutting member and the reference radial 53 of the drill body, which in
By the term “point of interest P” is meant any one of the numerous points on the cutting structure (in the prescribed range of values for λ and t), all of which must be considered in the solution to the system of equations. According to the convention adopted here, the angles α1 and α2 as shown in
wherein {right arrow over (A)} represents the direction vector of the rotatable cutting member axis and is given by:
{right arrow over (A)}=−sin(α1)·cos(α2),−cos(α1)·cos(α2), sin(α2) Eqn. 3
wherein {right arrow over (Tn)} represents the tangent to the helix passing through the point of interest Pti, on the cutting structure with coordinates (xi, yi, zi); the direction vector for {right arrow over (Tn)} being given by:
wherein the parameters ri and θi represent the polar coordinates of the point of the interest relative to the drill body axis of rotation, ri being the radius of the circle of rotation for that point, whereby ri and θi are given by:
The coordinates of the point of interest Pti, are given by:
xi=−Rb+sin(α1)·cos(α2)·(d−t)+rc·cos(λ)·cos(α1)−rc·sin(α2)·sin(λ)·sin(α1) Eqn. 7
yi=cos(α1)·cos(α2)·(d−t)−rc·sin(α2)·sin(λ)·cos(α1)−rc·cos(λ)·sin(α1) Eqn. 8
zi=−rc·sin(λ)·cos(α2)·sin(α2)·(d−) Eqn. 9
and for where condition 2 is true; rr is given by:
rr=rc−√{square root over ((xi−xr)2+(yi−yr)2+(zi−zr)2)} Eqn. 10
wherein xr, yr, zr are the coordinates of the centre of the rear face of the cutting structure and are given by:
xr=−Rb+sin(α1)·cos(α2)·(d−T) Eqn. 11
yr=cos(α1)·cos(α2)·(d−T) Eqn. 12
zr=−sin(α2)·(d−T) Eqn. 13
The parameter f, representing the hole forming tool translation per revolution during use, is limited by the available drilling torque and/or the maximum permissible loads and drilling speeds for the hole forming tool. Where more than one cutting structure bears a portion of the cutting load on a given circle of rotation about the axis of the drill body, the maximum depth of engagement of each cutting structure is some fraction of the translation per revolution and this should not generally exceed the radius of the cutting structure. More preferably, it does not exceed about half the radius of the cutting structure, so as to ensure the integrity of the rotatable cutting member and associated journal or roller element bearings. Furthermore, in those embodiments of the invention wherein cutting structures are bonded to rotatable cutting members by means of a braze layer or where the materials from which cutting structures are composed have limited thermal stability, the maximum depth of engagement of a cutting structure may be further limited. The maximum operating temperature is proportional to the product of hole forming tool rotational speed and torque. Torque in turn is proportional to the cross sectional area of cut, the hole forming tool translation per revolution and the hardness of the material being drilled. When forming holes in very hard materials and or at high rotational speed, the maximum depth of engagement for cutting structures is preferably limited to rc/3 or even rc/4. Several cutting structures may engage the material in which a hole is to be formed at any given circle of rotation. The hole forming tool translation per revolution is preferably limited such that it does not substantially exceed rc/2 or at most does not exceed rc. In practice, the majority of hole forming operations are limited by available drilling torque such that f is typically seldom greater than about 6 or 7 mm.
For the or each engagement region on a cutting structure, γeff max will preferably be less than a maximum value so as to result in robust cutting structures and this maximum value is discussed below. The configuration of the cutting structures and the resulting overlap guides the selection of a specific combination of the parameters α1, α2, d, T, Rb and rc. More particularly, the degree of overlap between cutting structures may be varied so as to avoid excessively large minimum necessary clearance angles and consequently, excessively large maximum effective clearance angles γeff max.
Certain combinations of the parameters α1, α2, d, T, Rb and rc result in an identical cutting structure geometry as certain other combinations of these parameters. With reference to
Rba+da2·Rba·da·sin(α1a)=Rbb2−2·Rbb·db·sin(α1b) Eqn. 14
Most hard cutting tool materials tend to be relatively weak in tension and vulnerable to fracture where a cutting edge is provided with an excessively large clearance angle. Cutting materials of different mechanical properties may permit smaller or larger clearance angles and hence, a greater range of permissible angles of inclination.
Hard cutting tool materials may exhibit tensile strengths as low as 1200-1500 MPa and relatively low Weibull moduli. Preferably, a margin of safety of, for example 2 to 3, is used such that cutting structures configured on the hole forming tool and using cutting materials known in the art have a maximum effective clearance angle of not more than about 45° over the majority of each engagement region of the cutting edge. Insofar as it represents the majority of cases, this limit for γeff max forms the basis of subsequent disclosure. Where it is necessary to form holes in extremely hard materials and/or with impact loading, the maximum effective clearance angle γeff max is preferably about 35°.
This criteria concerning γeff max may be subject to a certain allowance where the depth of engagement is small relative to the size of any bevels, radii or combinations of same disposed at the cutting edge. By the term ‘cutting edge’ is meant the outermost aspect of the cutting face of a cutting structure relative the axis of the rotatable cutting member; the cutting face including any bevels or radii disposed at the cutting edge. Edge bevels and radii are preferably limited in size to a fraction of the anticipated depth of engagement, as very high cutting forces will otherwise result. The effective depth of engagement varies along the engagement region of a cutting structure, decreasing towards the innermost and outermost extremities of the engagement region.
This point is illustrated in
At the position marked x-x in
With reference to
Preferably, the majority of cutting structures disposed on the drill body each overlap with at least one other cutting structure, said other cutting structure being rotatable in accordance with the present disclosure or in accordance with prior art cutting structures, and the values for λ1 and λ2 which denote the extremities of the engagement region are determined accordingly. While the maximum permissible effective clearance angle criterion applies over a majority of the each projected engagement length independently, the minimum necessary clearance angle must be determined over the entire interval [λ1, λ2] and where multiple engagement regions exist on a cutting structure, over the entire set Γ, Γ comprising multiple sub-sets, each sub-set being the interval [λ1, λ2] for each engagement region.
-
- Point 69 is the innermost possible position of the innermost extremity of the engagement region on cs_4
- Point 70 is the outermost possible position of the outermost extremity of the engagement region on cs_3
- Point 71 is both the innermost possible position of the outermost extremity of the engagement region on cs_3 and the outermost possible position of the innermost extremity of the engagement region on cs_4
- Point 72 is the innermost extremity of the engagement region on cs_3
- Point 73 is the innermost extremity of the engagement region on cs_4
For the purposes of determining the angles λ1 and λ2, point 69 is preferably the innermost extremity of the engagement region on cs_4 and point 70 preferably the outermost extremity of the engagement region on cs_3. Adopting points 69 and 70 as the extremities of the engagement regions avoids otherwise more complex calculations which would incorporate the relative angular positions of the cutting structures about the drill body axis of rotation, such complexities providing little practical benefit. This approach provides a slightly more conservative estimate for the minimum necessary clearance angle and the maximum effective clearance angle; both quantities will be over-estimated by no more than several degrees in the worst case.
λ1 and λ2 for cs_3 are denoted λ13 and λ23. λ1 and λ2 for cs_4 are denoted λ14 and λ24. Each of λ13, λ23, λ14 and λ24 are the sum of two angular quantities as given by Equations 15-18, where λ13a and λ24a are 0° and 180°, respectively, by definition and the other quantities are as depicted in
λ13=λ13a−λ13b=−A sin(f/2·R3) Eqn. 15
λ23=λ23a+λ23b Eqn. 16
λ14=λ14aλ14b Eqn. 17
λ24=λ24a−λ24b=180°+A sin(f/2·R4) Eqn. 18
The angular quantities in Equations 16 and 17 are determined from the parameters, R3, R4, IX and f. A similar methodology, as presented here for cs_3 and cs_4 is readily extended to any arrangement of cutting structures whose axes are inclined relative to a transverse plane of the drill body and or to reference radials of the drill body and where the cutting face centres may lie in different transverse planes of the drill body.
With regard to
The precise conditions of use of the hole forming tool, including the translation per revolution f, and hence the precise values for λ1 and λ2 are rarely known in advance and in many applications may vary over the lifetime of the hole forming tool. It is, however, generally preferable that γeff max is not substantially greater than about 45° over at least about 80% of the projected engagement length of each cutting edge of each rotatable cutting member on the drill body. The following examples illustrate the influence of the parameters α1, α2, Rb, d and T on the minimum necessary clearance angle and the resulting maximum effective clearance angle on isolated cutting structures. Subsequent examples deal with overlapping cutting structures.
Concerning the format and significance of the data, reference is now made to the upper right chart in
Certain combinations of the angles of inclination α1 and α2 and parameters d and T in
Not all combinations of the parameters α1, α2, d, T and Rb permit a relatively large cutting structure radius of rc=0.9·Rb, such that the maximum effective clearance angle γeff max is not substantially larger than about 45° over about 85% of the projected engagement length L. Examples of such are found in the third row of charts in
With regard to curve (iv) in
For hole forming tools which comprise multiple cutting structures, the cutting structures are preferably configured such that their cutting edges overlap when projected about the axis of drill rotation onto a radial plane of the drill body. The degree of overlap is expressed as that which results in a certain percentage reduction in the projected engagement length L of the cutting structure of interest. Two cases are considered hereinbelow: firstly, where the projected engagement length L of the cutting edge of a cutting structure of interest is reduced by 15% at its innermost aspect (more proximal the drill body axis) and secondly, where the projected engagement length L is reduced at the outermost aspect of the cutting structure.
Tables 1 and 2 detail several geometrical parameters of hole forming tools in accordance with the present disclosure, all such parameters being dependent on α1, α2, d, T, and Rb. Each of Tables 1 and 2 comprise 20 sub-tables arranged in four rows and five columns. Within each sub-table, α1 varies from −20° to 40° and α2 varies from 0° to 50°. The sub-tables in different rows differ in the relative values for d, T and rc, all expressed as a fraction of Rb. For example, in row (a), d=T=rc/3. All other length dimensions are expressed as fractions or multiples of Rb which is set to unity.
The first column in each of Tables 1 and 2 notes the maximum permissible cutting structure radius for the stated values of α1, α2, Rb, d and T so as to ensure the maximum effective clearance angle γeff max is 45° or less where that cutting structure is not overlapped by an adjacent cutting structure. The second column in Table 1, labelled ‘2.a)’, notes the maximum permissible cutting structure radius rc, for the stated values of α1, α2, Rb, d and T so as to ensure the maximum effective clearance angle γeff max does not exceed 45° where the outermost 15% of the projected edge length is shielded by another adjacent overlapping cutting structure. The second column in Table 2, labelled ‘2.a)’, notes the maximum permissible cutting structure radius rc for the stated values of α1, α2, Rb, d and T so as to ensure the maximum effective clearance angle γeff max does not exceed 45° where the innermost 15% of the projected edge length is shielded. The third column in each of Tables 1 and 2, labelled ‘2.b)’, shows the minimum necessary clearance angle, which must be provided on an otherwise cylindrical cutting structure so as to avoid interference between the side surface of that cutting structure and the surface of the formed hole. These values for the minimum necessary clearance angle are determined where the stated degree of overlap exists (and not for the isolated cutting structure referenced in column 1). While 15% overlap is relatively small—in practice, it often being 50% or greater—it better serves to demonstrate the effect of cutting structure overlap on the permissible combinations of the parameters α1, α2, d, T, Rb and rc. A larger degree of overlap would permit a broader range of parameter combinations as will be determinable following the present disclosure.
Concerning the format and significance of the data in Tables 1 and 2, it is useful to consider three examples in more detail. For an isolated cutting structure, where the angles α1 and α2 are each independently 20° and where d=T=rc/3 (row a of Table 1), the maximum permissible cutting structure radius is 0.6·Rb so as to ensure the maximum effective clearance angle γeff max is 45° or less. For a cutting structure with the same parameters α1, α2, Rb, d and T which is overlapped at its outmost region by an adjacent cutting structure, the maximum permissible cutting structure radius is 0.8·Rb so as to ensure γeff max is 45° or less (Table 1, column 2.a). The minimum necessary clearance angle on is 0° (Table 1, column, 2.b). For an isolated cutting structure where the angles α1 and α2 are each independently 20° and where d=T=rc/3 (row a of Table 2), the maximum permissible cutting structure radius is 0.6·Rb so as to ensure the maximum effective clearance angle γeff max is 45° or less. For a cutting structure with the same parameters which is overlapped at its innermost region, the maximum permissible cutting structure radius is 0.7·Rb so as to ensure γeff max is necessary 45° or less. The minimum clearance angle in this case is 8°. For an isolated cutting structure where the angles α1 and α2 are both 40° and where d/2=T=rc/2 (row c of Table 1), it is not possible to achieve a maximum effective clearance angle γeff max of 45° or less; i.e., the maximum permissible cutting structure radius is 0 (or at least no greater than 0.05 considering the resolution of the data). For a cutting structure with the same parameters which is overlapped at its outermost region the maximum permissible cutting structure radius is 0.6·Rb to ensure γeff max is 45° or less. This cutting structure may be of cylindrical form; i.e., the minimum necessary clearance angle is 0°.
Some general relationships may be observed in Tables 1 and 2. The maximum permissible cutting structure radius for a given combination of α1, α2, Rb, d and T is more strongly influenced by shielding the innermost region of its cutting edge, in comparison to shielding its outermost region of its cutting edge. Providing overlap at the outermost aspect of a cutting structure has less benefit in terms of reducing the minimum necessary clearance angle, compared to providing the same degree of overlap at the innermost aspect of that same cutting structure. Increasing the angle of inclination α2 generally results in a decrease the minimum necessary clearance angle.
The resolution in Tables 1 and 2 for the maximum permissible cutting structure radius rc, is limited to +1-0.05·Rb (in the worst case) and the minimum necessary clearance angles are rounded to the nearest degree. Greater precision may be derived following Equations 1-13. Alternatively, intermediate or other values may be adopted for each parameter without deviating from the present disclosure, as may alternate combinations of the parameters d, T and rc; as for example described by Equation 14. Furthermore, adopting different and or varying degrees of overlap are obvious extensions of the methodology disclosed here, as is configuring cutting structures which may be overlapped at their innermost, outmost and or more central regions (and Table 3 outlines several such scenarios). Similarly, alternately structured relationships will convey substantially the same meaning; whereby for example, one may determine the maximum permissible values for the parameter α1 where the parameters rc, α2, Rb, d and T are specified and where the maximum effective clearance angle may or may not be substantially greater than a value other than 45° or 35° or any other limit defined on the basis of a specific application.
Referring again to
Superimposed on each of these cutting structures are two triangles, which represent cones in three dimensions. The base radius of the cones is equal to the dimension rr—i.e., the radius of the rear face of the cutting structure after the minimum necessary clearance angle has been provided. It is reiterated here that reference to ‘cutting structure’ incorporates any adjacent, supporting region of the rotatable cutting member, which too is provided with the minimum necessary clearance angle. The height of the first cone in each case in
These cones (depicted as triangles in
In the most general sense, the rr dimension is preferably not substantially less than about 0.5·rc as otherwise, it will generally be found that there is insufficient space available for sealing elements and bearings of adequate size. The bearings must resist the forces acting on the cutting face of the cutting structures disposed on the rotatable cutting member and these forces generally act over a longer moment arm to that which can exist within the bearings. Furthermore, said bearings must reside within the annular region occupied by the seal elements. Consequently, it is preferable that the minimum value for rr is 0.7·rc. Regarding the maximum of the dimensions Lsa and Lsb, it is preferable that this at least equals the rr dimension and more preferably about twice the rr dimension. The construction of the shaft within the available volume is preferably subject to the known art in terms of optimising the ratio of shaft diameter to length, including for example, using stepped cantilever shafts. Where a sufficient volume of material is available for the construction of a sturdy bearing housing in the drill body, it is also necessary to ensure an adequate cross sectional area for the cantilever shaft where it adjoins the rotatable cutting member. Similarly, where a sufficient volume of material is available for the construction of a sturdy bearing housing in the rotatable cutting member, it is also necessary to ensure an adequate cross sectional area for the cantilever shaft where it adjoins the drill body.
Columns 2.c and 2.d in each of Tables 1 and 2 show the dimensions rr and Lsb respectively. Lsb is determined on the basis of the maximum effective clearance angle γeff max being 45° or less and 15% overlap at the indicated location on the cutting structure. The parameters rr is expressed as a fraction of rc, and Lsb, as a multiple of rc. According to the convention adopted here, the Lsa values are equal to the cutting structure thickness T and in the present examples therefore, always less than the Lsb values. rr is between 0.8·Rb-1.0·Rb, while Lsb is generally equal to or greater than 1.4 (it being slightly less than 1.4 in only five instances in Table 1 and in only four instances in Table 2). Where multiple cutting structures are disposed on a rotatable cutting member, the Lsa parameter may be greater in value, with a corresponding reduction in the value of the parameter Lsb.
The characteristics of the un-deformed cross sectional area of cut on the or each cutting structure is an important aspect of realising in accordance with the present disclosure optimum combinations of at least, the angles of inclination, cutting structure radius and the position of cutting structures along the rotatable cutting member.
Table 3 provides non-limiting examples of the present invention in which there are inner and outer arrangements of rotatable cutting members, each positioned at a distance Rb from the drill body axis of rotation. In Examples 1 to 3 of Table 3, two cutting structures are disposed on each of the inner and outer rotatable cutting members. In Examples 4 to 6, three cutting structures are disposed on the outer rotatable cutting member with one cutting structure on the inner rotatable cutting member. In each of Examples 1 to 6 and solely for the purposes of illustration, the diameter of the hole produced by the disclosed embodiments is approximately 240 mm. Example 7 shows three rotatable cutting members positioned on different circles of rotation, the first positioned more inwardly with respect to the tool body axis, the third, positioned more outwardly with respect to the tool body axis and the second, in an intermediate position. The angles α1 and α2 are as described above and as depicted in
In Table 3, the radius of the cutting structures is denoted by the rc values which are subscripted by the cutting structure number each refers to. The dimension T in Table 3 denotes the thickness of the first cutting structure disposed on the proximal end (with respect to the drill body) of each rotatable cutting member. The dimension d for this first cutting structure on each rotatable cutting member is zero. Where a second cutting structure is disposed on the same rotatable cutting member, this is positioned such that the plane containing the cutting edge of said structure is positioned at a distance ‘d_12’ from the face of the first cutting structure. A third cutting structure disposed on the same rotatable cutting member as cutting structures C1 and C2 is positioned at a distance ‘d_23’ from the face of the second cutting structure and in this case, cutting structure C3 is leading cutting structure C2 in the sense of hole forming tool rotation, and cutting structure C2 is leading cutting structure C1. If cutting structures C1 and C2 are disposed on a first rotatable cutting member and cutting structures C3 and C4 are disposed a second rotatable cutting member, the d_23 parameter is not applicable. If cutting structures C2, C3 and C4 are disposed on the same rotatable cutting member, the parameter d_12 is not applicable.
In each example non-limiting and solely for the purposes of illustration, the hole forming tool translation per revolution is 3 mm. For simplicity, the hole forming tool in Examples 1 to 6 comprises only two rotatable cutting members and in Example 7, only three rotatable cutting members. Hence, the maximal possible depth of engagement on any cutting structure is 3 mm, though as will become apparent, only certain cutting structures experience this maximal value. It will usually be the case that multiple cutting structures engage the material in which a hole is to be formed at any particular circle of rotation and the depth of engagement is reduced in proportion to the number of cutting structures.
The γ_min_n values in Table 3 represent the minimum necessary clearance angle for cutting structure Cn. A negative angle indicates that there is no interference arising on a cutting structure of cylindrical form. Where a positive minimum necessary clearance angle is indicated, the cutting structure is of substantially conical form, the apex angle of the cone being at least twice the stated value so as to avoid interference. An additional amount of clearance is desirable to the minimum necessary angle determined from geometrical considerations—which, not wishing to bound by way of illustration and depending on the properties of the cutting structure material, is within the range of from less than 5° to as great as 20°.
The angle denoted γeff max n represents the maximum effective clearance angle subtended between the clearance face of cutting structure Cn which has been provided with the minimum necessary clearance, and the newly formed surface of the hole. The values for the maximum effective clearance angle cited in Table 3 include five degrees additional clearance beyond the minimum necessary values. Where γ_min is 0° or less the clearance angle relative to the rotatable cutting member axis of rotation is 5°. This additional five degrees clearance provides more space for the evacuation of cuttings. Further clearance may be provided for example in the form of a second concentric conical surface of a larger apex angle.
In Example 1 of Table 3, cutting structure C2 on the inner rotatable cutting member is required to have a minimal clearance angle of 6.1°. Including five degrees of additional clearance, this results in a maximum effective clearance angle γeff max of 24°. For cutting structures C1 and C4, the minimum necessary clearance angle is negative; the minimum effective clearance angle subtended on the side face of cylindrical cutting structures is 8.7° and 5.2°, respectively.
In Example 2 of Table 3, α1 for the inner rotatable cutting member is 20°, which represents a more inwardly orientated inclination of the rotatable cutting member axis relative to Example 1. This reduces the minimum necessary clearance angle on cutting structure number 2 such that with a cylindrical cutting structure, the minimum effective clearance angle is 7.2°. The maximum effective clearance angle γeff max on cutting structure C1 is thus reduced significantly relative to the same cutting structure in Example 1, while for cutting structure C2, it is increased slightly. This arises because in Example 2, the innermost aspect of cutting structure C1 is shielded by cutting structure C2, whereas in Example 1, the innermost aspect of cutting structure C2 is shielded by cutting structure C1.
In Example 3 of Table 3, the inner rotatable cutting member is 5 mm closer to drill body axis compared to Example 2. This increases the minimum necessary clearance angles for both cutting structures C1 and C2. It also significantly increases γeff max for cutting structure number C2. For cutting structures C3 and C4 in Examples 1-3, the configuration of the rotatable cutting member on which these are disposed is constant. The changes in the respective values for the minimum necessary and maximum effective clearance angles arise from the variation in the degree of overlap with cutting structures C1 and C2.
With regard to Example 4 in Table 3, the particular angles of inclination of the outer rotatable cutting member provides for negative minimum necessary clearance angles for cutting structures C3 and C4. For cutting structure C1, while the minimum necessary clearance angle is only 7.7°, the maximum effective clearance angle γeff max is 42.8°. Though large, this occurs only near the innermost aspect of the cutting structure. Over the outermost 75% of this cutting structures projected edge length, the effective clearance angle is 30° or less. The variation in the effective clearance angle as a function of drill body radial position for cutting structure C1 is similar to the curve for rc=0.6·Rb in the lower left chart in
With regard to Example 5 in Table 3, the angle α2 for the outer rotatable cutting member has increased to 20°, thereby increasing the minimum necessary clearance angles for cutting structures C2 and C4. The maximum effective clearance angles are also significantly larger; cutting structure C2 for example now has a maximum effective clearance angle γeff max of 45.6°. If, by way of illustration, cutting structure C2 were not shielded by other cutting structures, γeff max would be about 64°. With reference to
With reference to Example 6 in Table 3, in comparison to the maximum depth of engagement for cutting structure C2 of 2.7 mm in Example 5, the corresponding value in Example 6 is 1.8 mm—illustrated by the shaded region at right in
With reference to
The distribution of rotatable cutting members, according to the configurations in Table 3, on the working face of the hole forming tool may be varied. The number and relative angular positioning of the rotatable cutting members on their respective circles of rotation may be uniform or non-uniform. With regard to both aspects, numerous differing permutations are possible. In all the above non-limiting examples, one or more of the rotatable cutting members may be replaced with non-rotatable or are rotatable prior art cutting structures.
It is to be understood that the invention is not limited to the specific details described herein which are given by way of example only and that various modifications and alterations are possible without departing from the scope of the invention as defined in the appended claim.
Claims
1. A hole forming tool (16, 26, 29) operable with a translation per revolution f and comprising a rotatable drill body (17) having γ eff max = ( Max λϵΓ; t = 0 ( χ · A cos ( Tn → · A → Tn → · A → ) ) ) - ( Min λϵ [ λ 1, λ 2 ]; t = 0 ( χ · A cos ( Tn → · A → Tn → · A → ) ) ) applicable where ( Max λϵΓ; t = 0 ( χ · A cos ( Tn → · A → Tn → · A → ) ) ) ≥ ( Max λϵΓ; t = T ( χ · A cos ( Tn → · A → Tn → · A → ) ) ) Equation ( 1 ) γ eff max = ( Max λϵΓ; t = T ( A tan ( r c - r r T ) ) ) - ( Min λϵ [ λ 1, λ 2 ]; t = 0 ( χ · A cos ( Tn → · A → Tn → · A → ) ) ) applicable where ( Max λϵΓ; t = 0 ( χ · A cos ( Tn → · A → Tn → · A → ) ) ) < ( Max λϵΓ; t = T ( χ · A cos ( Tn → · A → Tn → · A → ) ) ) Equation ( 2 ) Tn → = 〈 sin ( θ i ), - cos ( θ i ), ( f 2 · π · r i ) 〉; r i = x i 2 + y i 2 and θ i = A tan ( y i x i );
- a proximal end (19) for attachment to a drive mechanism and a distal end (21);
- a drill body axis of rotation defining a Z axis;
- mutually orthogonal axes X and Y, both X and Y axes intersecting at and orthogonal to the Z axis;
- whereby on the distal end (21) of the rotatable drill body (17) is disposed at least one rotatable cutting member (23), the or each rotatable cutting member (23) independently being substantially concentric with and supported by a cantilever shaft (35) and independently having
- a radial plane in which the Z axis lies;
- a first transverse plane (S2, 74) normal to the Z axis, with a proximal side towards the proximal end (19) of the rotatable drill body (17);
- a third transverse plane (75) towards the proximal side of the first transverse plane, the third transverse plane normal to the Z axis and at a distance f from the first transverse plane;
- a reference radial (53) defined by the intersection of the radial plane and the first transverse plane (S2, 74);
- a longitudinal plane (S1) parallel to the Z axis and subtending an angle α1 with a normal to the radial plane;
- an axis of rotation (A) lying in the longitudinal plane (S1), subtending an angle α2 to the first transverse plane and extending through an intersection point I; the intersection point I at the intersection of the radial plane and the first transverse plane and at a distance Rb from the Z axis;
- wherein on the or each rotatable cutting member (23) is disposed at least one cutting structure (24), the or each cutting structure independently having
- a cutting face centre (Oc, 64, 65) a distance d along the axis of rotation (A) from the intersection point I;
- a cutting face (54) of radius rc;
- a continuous cutting edge (C, cs_3, cs_4) which is substantially concentric with the axis of rotation (A);
- a thickness T extending from the cutting face centre (Oc, 64, 65) towards the intersection point I in the direction of the axis of rotation (A);
- a second transverse plane normal to the Z axis, through the cutting face centre (Oc, 64, 65) and having a proximal side towards the proximal end (19) of said rotatable drill body (17);
- a cutting face reference radial (56) defined by the intersection of the cutting face (54) and the second transverse plane; the cutting face reference radial (56) extending from the cutting face centre (Oc, 64, 65) towards the Z axis;
- a fourth transverse plane (76) normal to the Z axis, towards the proximal side of the second transverse plane and at a distance from the second transverse plane of one half of said translation per revolution f; the fourth transverse plane having a proximal side (78) and a distal side (77);
- a distal region of the continuous cutting edge (C, cs_3, cs_4) on the distal side (77) of the fourth transverse plane;
- wherein the distal region of the continuous cutting edge of a first of said the or each cutting structure independently has at least one engagement region, the or each engagement region having a first edge point (Pti) with coordinates xi, yi, zi on the X, Y and Z axes respectively, xi and yi defining a radius ri of a first circle of rotation about the Z axis;
- whereby on the distal region of a cutting edge of any second of said at least one cutting structure, a second edge point (Pti), having a circle of rotation about the Z axis of equal radius to said first circle of rotation about the Z axis, is less distal the first transverse plane (74) than the first edge point (Pti) is distal the third transverse plane (75);
- wherein the or each engagement region independently has
- an innermost extremity (72, 69) with respect to the Z axis;
- an outermost extremity (70, 73) with respect to the Z axis;
- a first cutting face radial extending from the cutting face centre (Oc, 64, 65) to the innermost extremity (72, 69);
- a second cutting face radial extending from the cutting face centre (Oc, 64, 65) to the outermost extremity (70, 73);
- a first cutting face angular coordinate λ1 subtended between the first cutting face radial and the cutting face reference radial (56);
- a second cutting face angular coordinate λ2 subtended between the second cutting face radial and the cutting face reference radial (56);
- wherein for the or each cutting face independently, Γ is a set comprising the angular intervals λ1, λ2 for the or each engagement region of said cutting face;
- and wherein the or each engagement region independently has a projected engagement length L (L_a1, L_a2), the or each projected engagement length L independently determined by firstly rotationally projecting the engagement region about the Z axis onto the radial plane to form a first projection and secondly thereafter, projecting said first projection parallel to the Z axis onto said reference radial (53);
- such that that the maximum effective clearance angle γeff max of the or each engagement region as defined by Equations (1) or (2) hereinbelow is independently not greater than 45° over at least 80% of the projected engagement length L of the or each engagement region:
- wherein {right arrow over (A)} is the rotatable cutting member axis direction vector and is given by: {right arrow over (A)}=−sin(α1)·cos(α2),−cos(α1)·cos(α2), sin(α2),
- and wherein {right arrow over (Tn)} is a vector given by:
- wherein 0≤f≤rc;
- wherein ri and θi are given by:
- wherein χ has a value of +1 if {right arrow over (Tn)} extends inwardly with respect to the rotatable cutting member axis of rotation and χ has a value of −1 if {right arrow over (Tn)} extends outwardly with respect to the rotatable cutting member axis of rotation and xi=−Rb+sin(α1)·cos(α2)·(d−t)+rc·cos(λ)·cos(α1)−rc·sin(α2)·sin(λ)·sin(α1), yi=cos(α1)·cos(α2)·(d−t)−rc·sin(α2)·sin(λ)·cos(α1)−rc·cos(λ)·sin(α1) and zi=−rc·sin(λ)·cos(α2)−sin(α2)·(d−);
- wherein the subscript i denotes a parameter determinable for any value of λ∈Γ;
- wherein rr is given by: rr=rc−√{square root over ((xi−xr)2+(yi−yr)2+(zi−zr)2)}
- wherein xr, yr, zr are given by: xr=−Rb+sin(α1)·cos(α2)·(d−T), yr=cos(α1)·cos(α2)·(d−T) and zr=−sin(α2)·(d−T).
2. A hole forming tool (16, 26, 29) as claimed in claim 1, wherein the maximum effective clearance angle γeff max is not greater than 45° over the projected engagement length L of the or each engagement region and wherein 0≤f≤rc/2.
3. A hole forming tool (16, 26, 29) as claimed in claim 2, wherein the maximum effective clearance angle γeff max is not greater than 35° over the projected engagement length L of the or each engagement region.
4. A hole forming tool (16, 26, 29) as claimed in claim 1, wherein on the periphery of at least one of the or each rotatable cutting member (23) is disposed at least one cutting structure (24).
5. A hole forming tool (16, 26, 29) as claimed in claim 1, wherein at least one of the or each cutting structure (24) is formed independently of and bonded to the rotatable cutting member (23) on which it is disposed.
6. A hole forming tool (16, 26, 29) as claimed in claim 1, wherein the rotatable drill body (17) has a direction of rotation about the Z axis and comprises a plurality of rotatable cutting members (23), the intersection point I of each of said plurality of rotatable cutting members (23) sharing a circle of revolution about the Z axis and wherein the angular position (ψ) of the reference radial (53) of a first rotatable cutting member relative to the reference radial (53) of a second rotatable cutting member is not equal to the angular position (ψ) of the reference radial (53) of the second rotatable cutting member relative to the reference radial (53) of the first rotatable cutting member, whereby all angular positions (ψ) are measured in the direction of rotation of the rotatable drill body (17).
7. A hole forming tool (16, 26, 29) as claimed in claim 1; wherein the rotatable drill body (17) comprises a plurality of rotatable cutting members (23); wherein the intersection point I of a first rotatable cutting member (23) lies on a first circle of rotation about the Z axis; wherein the intersection point I of a second rotatable cutting member (23) lies on a second circle of rotation about the Z axis; the diameter of said first circle of rotation being different to the diameter of said second circle of rotation.
8. A hole forming tool (16, 26, 29) as claimed in claim 1; wherein the rotatable drill body (17) comprises a plurality of rotatable cutting members (23); wherein;
- the angle α1 of a first rotatable cutting member (23) is different to the angle α1 of a second rotatable cutting member (23), and or;
- the angle α2 of a first rotatable cutting member (23) is different to the angle α2 of a second rotatable cutting member (23).
9. A hole forming tool (16, 26, 29) as claimed in claim 1, wherein the rotatable drill body (17) comprises a plurality of cutting structures (24) and wherein the cutting face (54) radius rc of at least one of said one or more cutting structures is different to the cutting face radius rc of another of said one or more other cutting structure (54).
10. A hole forming tool (16, 26, 29) as claimed in claim 1, wherein at least one rotatable cutting member (23) is integral with its cantilever shaft (35), and wherein said cantilever shaft (35) is received within a bore in the distal end (21) of the rotatable drill body (17).
11. A hole forming tool (16, 26, 29) as claimed in claim 1, further comprising at least one rotatable crushing member (10) wherein a plurality of indenter elements (11) is disposed on the surface of the or each rotatable crushing member (10).
12. A hole forming tool (16, 26, 29) as claimed in claim 1, wherein the or each cutting edge (C) is provided with at least one bevel (47) and or at least one radius (48).
13. A hole forming tool (16, 26, 29) as claimed in claim 1, wherein the cutting face (54) of the or each cutting structure (24) is polycrystalline in nature and includes diamond.
14. A hole forming tool (16, 26, 29) as claimed in claim 1, wherein the rotatable drill body (17) comprises flutes (18) and or reliefs (25) for conveying cuttings away from the distal end (21) of the rotatable drill body, preferably wherein said cut-outs are substantially longitudinal, substantially helical or a combination of linear and helical.
15. A hole forming tool (16, 26, 29) as claimed in claim 1, wherein the or each rotatable cutting member (23) is independently permitted to rotate relative to the rotatable drill body (17) by means of a roller element or journal bearing (36, 37) arrangement disposed on the cantilever shaft (35) associated therewith.
16. A hole forming tool (16, 26, 29) as claimed in claim 15, wherein the or each roller element or journal bearing (36, 37) arrangement is lubricated by a lubricant reservoir (40).
17. A hole forming tool (16, 26, 29) as claimed in claim 1, wherein the rotatable drill body (17) is of an integral construction.
18. A hole forming tool (16, 26, 29) as claimed in claim 15, wherein the rotatable drill body (17) includes a plurality of retaining balls (38).
19. A hole forming tool (16, 26, 29) as claimed in claim 1, wherein rc is not substantially greater than about 0.9·Rb.
20. A hole forming tool (16, 26, 29) as claimed in claim 19, wherein rc is not substantially less than about 0.3·Rb.
Type: Application
Filed: Jul 26, 2016
Publication Date: Oct 18, 2018
Inventor: John James Barry (Ennis)
Application Number: 15/735,167