Patent Description:
Steam turbines include static nozzle assemblies that direct flow of a working fluid into turbine blades (also referred to as buckets) connected to a rotating rotor. The nozzle construction (including a plurality of nozzles, or "airfoils") is sometimes referred to as a "diaphragm" or "nozzle assembly stage. " Blades, such as those in the last stage of the turbine, have a base with a dovetail that are sized to fit within corresponding dovetail slots in the rotor. The documents <CIT> and <CIT> show such dovetail configurations. Many last stage blades are of significant length and have a substantial weight. During low speed (also known as, turning gear) operation, the blades have the ability to move within the rotor dovetails where they are retained. This undesirable movement can cause significant wear on the blade and/or rotor dovetail slots. This wear on the blades and dovetail slots can cause outages, require repairs, and result in undesirable costs.

During rotor assembly, it is required to have some movement ("fanning") of the blades to facilitate assembly of the blades. The blades have outer cover ends and these typically have interlocking features. The blades must pass each other during assembly of the previous blade during row assembly. The blades may also overlap airfoils such that assembly of the last blades in the row may be difficult, if not impossible, to assemble if adequate movement does not exist.

The invention is directed to a turbine rotor having a rotor body with a plurality of dovetail slots including a plurality of recesses. A turbine blade is located within one of the plurality of dovetail slots. The turbine blade has a blade/airfoil having a first end, and a second end opposite the first end. A tip is at an outer radial portion of the blade, and a base is at an inner radial portion of the blade. The base includes a dovetail for complementing a corresponding dovetail slot in the turbine rotor. The dovetail has a body and a plurality of projections extending from the body in opposing directions for complementing a plurality of recesses in the corresponding dovetail slot. A tapered groove extends through the body from the first end to the second end. The tapered groove has a tapered profile such that a first depth of the tapered groove near the first end is greater than a second depth of the tapered groove near the second end. The tapered profile gradually transitions from the first depth to the second depth, and the tapered groove is open at a bottom surface of the body and sized to engage a shim. The shim retains the turbine blade in the dovetail slot, the shim includes: a main body having a first thickness measured between an upper surface and a lower surface, and a second thickness measured between the upper surface and the lower surface, the first thickness located near a first end of the shim and the second thickness located near a second end of the shim, the first end generally opposing the second end, the first thickness being greater than the second thickness;a thinned region extending from the main body and having a third thickness measured between the upper surface and a thinned, lower surface, the thinned region located at the first end.

These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the disclosure, in which:.

It is noted that the drawings of the invention are not necessarily to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention.

The subject matter disclosed herein relates to turbomachines. Specifically, the subject matter disclosed herein relates to supporting blades in turbomachines, e.g., steam turbines.

As denoted in these Figures, the "A" axis represents axial orientation (along the axis of the turbine rotor, sometimes referred to as the turbine centerline). As used herein, the terms "axial" and/or "axially" refer to the relative position/direction of objects along axis A, which is substantially parallel with the axis of rotation of the turbomachine (in particular, the rotor section). As further used herein, the terms "radial" and/or "radially" refer to the relative position/direction of objects along axis (r), which is substantially perpendicular with axis A and intersects axis A at only one location. The phrase "radially inward" is in a direction facing the A-axis or axis of the turbine rotor, and "radially outward" is in a direction opposite to radially inward, or in a direction away from the A-axis. Additionally, the terms "circumferential" and/or "circumferentially" refer to the relative position/direction of objects along a circumference (c) which surrounds axis A but does not intersect the axis A at any location. Identically labeled elements in the Figures depict substantially similar (e.g., identical) components.

In contrast to conventional components and approaches for retaining blades in steam turbines, various aspects of the disclosure provide for a steam turbine blade, and a corresponding retaining shim, which enhance the ease of installation and/or removal of blades from steam turbine rotors, as well as improve the retention of those blades within the rotor. Conventional systems for retaining blades within rotors utilize combinations of shims, springs and tight-fitting dovetail connections. These systems can occupy a significant amount of space, be difficult to install, and/or cause stresses on components such as the blade dovetail or rotor dovetail due to their tight fit and limited flexibility. The components disclosed according to various embodiments described herein can be installed with much less effort than conventional configurations, and provide for enhanced retention during operation.

Turning to <FIG>, a partial cross-sectional schematic view of steam turbine <NUM> (e.g., a high-pressure / intermediate-pressure steam turbine) is shown. Steam turbine <NUM> may include, for example, a low pressure (LP) section <NUM> and a high pressure (HP) section <NUM> (it is understood that either LP section <NUM> or HP section <NUM> can include an intermediate pressure (IP) section, as is known in the art). The LP section <NUM> and HP section <NUM> are at least partially encased in casing <NUM>. Steam may enter the HP section <NUM> and LP section <NUM> via one or more inlets <NUM> in casing <NUM>, and flow axially downstream from the inlet(s) <NUM>. In some embodiments, HP section <NUM> and LP section <NUM> are joined by a common shaft <NUM>, which may contact bearings <NUM>, allowing for rotation of shaft <NUM>, as working fluid (steam) forces rotation of the blades within each of LP section <NUM> and HP section <NUM>. After performing mechanical work on the blades within LP section <NUM> and HP section <NUM>, working fluid (e.g., steam) may exit through outlet <NUM> in casing <NUM>. The center line (CL) <NUM> of HP section <NUM> and LP section <NUM> is shown as a reference point. Both LP section <NUM> and HP section <NUM> can include diaphragm assemblies, which are contained within segments of casing <NUM>.

<FIG> shows a schematic perspective view of a steam turbine blade <NUM> (e.g., within LP section <NUM>) according to various embodiments of the disclosure. <FIG> shows a close-up perspective view of a portion of the steam turbine blade <NUM>. As shown, steam turbine blade (or bucket) <NUM> can include a blade or airfoil <NUM> having a radially outer first end <NUM>, and a radially inner second end <NUM> opposite first end <NUM>. First end <NUM> of blade <NUM> can include a tip <NUM>, which may be coupled to a shroud (not shown) in some embodiments. At second end <NUM> of blade <NUM> is a base <NUM>, which includes a dovetail <NUM> for engaging with and complementing a corresponding dovetail slot in a rotor (<FIG>).

<FIG> shows a close-up perspective view of a portion of a rotor <NUM> (e.g., a steam turbine rotor) including a dovetail slot <NUM> for coupling with dovetail <NUM> of blade <NUM>. In <FIG>, a tapered groove <NUM> extends along the bottom (radially inner) portion of the dovetail <NUM>. The blade <NUM> includes a first end <NUM> and a second end <NUM>. The first end <NUM> may be a leading edge of the blade and the second end <NUM> a trailing edge of the blade, or vice-versa. The tapered groove <NUM> is deeper (i.e., extends radially deeper into the dovetail) near the first end, and the depth of the groove <NUM> gradually reduces at it extends to the second end <NUM>. As one non-limiting example only, the depth of the tapered groove <NUM> near the first end <NUM> may be about <NUM> inches and the depth of the groove <NUM> near the second end <NUM> may be about <NUM> inches. A blended region <NUM> is located on the axially facing and opposing surfaces (or upstream and downstream facing surfaces) of the rotor <NUM> or wheel at the radially inner portion of slot <NUM>. The blended region <NUM> has a radiused surface and it assures a proper bend radius of the wedge/shim such that no cracking will occur in the wedge/shim when it is bent over the rotor <NUM> (as shown in <FIG>) or blade dovetail (as shown in <FIG>).

Returning to <FIG>, in contrast to conventional steam turbine blades, blade <NUM> can include dovetail <NUM>, which includes: a body <NUM>, a plurality of projections <NUM> extending from the body in opposing directions (d<NUM>, d<NUM>), and a tapered groove <NUM> extending through body <NUM> along the length of the dovetail. The plurality of projections <NUM> are sized to complement a plurality of recesses <NUM> in the corresponding dovetail slot <NUM> (<FIG>). In various embodiments, tapered groove <NUM> is open at a bottom surface <NUM> of body <NUM>, and is sized to engage a shim (<FIG>). Tapered groove <NUM> extends entirely through body <NUM> and is open at the bottom thereof. In various embodiments, body <NUM> includes a lowermost bulbous section <NUM> for complementing one of the plurality of recesses <NUM> in dovetail slot <NUM> (<FIG>). A shim <NUM> is shown schematically in <FIG>, and in a close-up perspective in <FIG>, and further described herein.

Blade <NUM> can further include an axial retention feature <NUM> extending from a side <NUM> of body <NUM> in a direction (dp) perpendicular from the plurality of projections <NUM>. That is, axial retention feature <NUM> can extend from side <NUM> of body <NUM> in direction (dp) that is perpendicular to the opposing directions (d<NUM>, d<NUM>). In some cases, axial retention feature <NUM> can include a hook <NUM>, having a first member <NUM> extending from body <NUM> in a first direction (direction dp), and a second member <NUM> extending from first member <NUM> in a second, distinct direction (dh2). In various embodiments, second, distinct direction (dh2) is perpendicular to first direction (dp). As described further herein, axial retention feature <NUM> is configured to aid in axially retaining blade <NUM> in rotor <NUM> (in axial direction, A), via an axial retention member <NUM> (<FIG>, <FIG>). In various embodiments, axial retention feature <NUM> defines a space <NUM> adjacent body <NUM> that is sized to engage the axial retention member <NUM>. Space <NUM> may be located between axial retention feature <NUM> and side <NUM> of body <NUM> in some embodiments. <FIG> shows a schematic cut-away depiction of blade <NUM> engaged with rotor <NUM>, and portion of an axial retention member <NUM> within space <NUM> for axially retaining blade <NUM> within rotor <NUM>. <FIG> shows a perspective radially outwardly facing view of axial retention member <NUM> positioned relative to rotor <NUM>, excluding blade(s) <NUM>. In some cases, axial retention member <NUM> further includes an anti-rotation tab <NUM> (<FIG>) for engaging hook <NUM> (<FIG>) and preventing rotation of axial retention member <NUM> within space <NUM> (<FIG>, <FIG>). Additionally, an anti-rotation pin <NUM> (<FIG>) can be coupled to rotor <NUM> to prevent radial movement of axial retention member <NUM> within space <NUM>.

Returning to <FIG> and <FIG>, shim <NUM> is shown in greater detail. In various embodiments, shim <NUM> is sized to engage tapered groove <NUM> in blade <NUM> and help to retain blade <NUM> within dovetail slot <NUM> (<FIG>). In some cases, shim <NUM> includes a main body <NUM> having a first thickness (t<NUM>) measured between an upper surface <NUM> and a lower surface <NUM> of main body <NUM> (where upper and lower surfaces <NUM>, <NUM> coincide with radially inner and radially outer surfaces, respectively, when shim <NUM> is loaded between blade and rotor <NUM> in dovetail slot <NUM>). Extending from main body <NUM> is a thinned region <NUM>, having a second thickness (t<NUM>) measured between upper surface <NUM> (which is continuous between main body <NUM> and thinned region <NUM>) and a thinned, lower surface <NUM>. In some cases, the second thickness (t<NUM>) is between approximately (e.g., +/- <NUM>-<NUM>%) <NUM> percent to approximately <NUM> percent of the first thickness (t<NUM>). Connecting main body <NUM> and thinned region <NUM> is a first tapered region <NUM>, which is tapered inward from main body <NUM> to thinned region <NUM>.

As described herein, shim <NUM> is configured to fit in tapered groove <NUM> and between dovetail <NUM> of blade <NUM>, and dovetail slot <NUM> of rotor <NUM>, and aid in retaining blade <NUM> within rotor <NUM>. Further, in various embodiments, thinned region <NUM> enhances ease of installation and removal of shim <NUM> within the tight clearances of the steam turbine. That is, thinned region <NUM> can permit flexion of shim <NUM> or bending over of an end of the shim to lock the shim to rotor <NUM>. The thinned region <NUM> is preferably located on the thicker end of the shim, as the thicker end would be more difficult to bend over than the opposing thinner end. The section <NUM> is thinned to assure proper bend to thickness ratio such that cold working will not result in cracking or a high residual stressed area. The reduced thickness facilitates bending over a portion of the shim to lock it to the rotor, and the opposing end portion near the thin end can also be bent over in a similar manner to lock the shim to rotor <NUM>. An important reason the bend-over is required at the thick end is because during operation the radial gap between the rotor dovetail bottom and the blade dovetail bottom can get larger due to mechanical growth. This radial gap would allow the wedge or shim to move towards the thin end during operation and then during shut down the radial gap would return to normal height. As the wedge/shim may have move forward and filled the larger gap there would be no room during shut-down for the blade to return to a non-stressed state. The radial gap being filled would result in excessive compression of the wedge/shim such that stresses could be beyond yield and/or disassembly of the wedge and it would be virtually impossible to remove the wedge/shim due to extremely high compression loading. It is understood that shim <NUM> can be inserted in either a forward or aft direction into slot <NUM>, depending upon clearances and desired installation techniques. In various embodiments, thinned region <NUM> can have a length (ITR) equal to approximately one-quarter of a length (lMB) of main body <NUM>, or one-eighth of a length of the main body, or three-sixteenths of a length of the main body, or between about <NUM>% and about <NUM>% of the length of the main body.

<FIG> and <FIG> illustrate perspective blown-out views of blade <NUM>, rotor <NUM> (<FIG>), and shim <NUM>. <FIG> also shows a section of rotor <NUM> including a plurality of dovetail slots <NUM>, as noted herein. In various aspects of the disclosure, a rotor <NUM> includes the plurality of dovetail slots <NUM>, and at least one blade <NUM> within one of the plurality of dovetail slots <NUM>. In some cases, an entire stage of a rotor <NUM> is assembled using blade(s) <NUM>, or multiple stages of rotor <NUM> are assembled using blade(s) <NUM>. As can be seen in <FIG> and <FIG>, tapered groove <NUM> is sized to complement shim <NUM>, and fit between dovetail <NUM> of blade <NUM> and dovetail slot <NUM> of rotor <NUM>.

<FIG> illustrates a simplified cross-sectional view of tapered groove <NUM>, according to various embodiments. The tapered groove <NUM> may include a flat section <NUM> near the first end <NUM> or the second end <NUM> (as shown), where the flat section <NUM> has a constant depth (i.e., it is not tapered). For example, the first end <NUM> may be a leading edge of the blade, and the second end <NUM> may be the trailing edge of the blade. The depth <NUM> of the tapered groove <NUM> at the deep end (left side of <FIG>) is greater than the depth <NUM> (and depth <NUM>) near the opposing end (right side of <FIG>). The flat section <NUM> has a constant depth <NUM> across its length. The length of flat section <NUM> may be about <NUM>% to about <NUM>% of the entire length of tapered groove <NUM>. The flat section <NUM> facilitates disassembly/removal of the shim <NUM> after turbine operation, and may also enable avoiding the use of a cut-off tool in the field during disassembly. Additionally, the flat section becomes the tertiary datum for machining and inspection of the blade as using the groove taper would not be prudent or robust.

<FIG> illustrates a simplified, cross-sectional view of shim <NUM>. The shim <NUM> includes a thick end and an opposing thin end, and the overall thickness gradually transitions between opposing ends. The thinned region <NUM> is a region of reduced thickness that enables the shim to be bent over the rotor or wheel to lock the shim in place. This is particularly effective when both ends of the shim are bent over the wheel/rotor, as the shim is prevented from moving in an axial direction (with respect to the turbine). For example, a first end of the shim <NUM> may have a first height <NUM>, and an opposing second end of the shim may have a second height <NUM>, where the first height is greater than the second height. The intermediate heights of the shim <NUM> gradually transition from the first height to the second height.

Blade <NUM> and/or shim <NUM> (<FIG>) may be formed in a number of ways. In one embodiment, blade <NUM> and/or shim <NUM> (<FIG>) may be formed by casting, forging, welding and/or machining. In one embodiment, however, additive manufacturing is particularly suited for manufacturing blade <NUM> and/or shim <NUM> (<FIG>). As used herein, additive manufacturing (AM) may include any process of producing an object through the successive layering of material rather than the removal of material, which is the case with conventional processes. Additive manufacturing can create complex geometries without the use of any sort of tools, molds or fixtures, and with little or no waste material. Instead of machining components from solid billets of plastic, much of which is cut away and discarded, the only material used in additive manufacturing is what is required to shape the part. Additive manufacturing processes may include but are not limited to: 3D printing, rapid prototyping (RP), direct digital manufacturing (DDM), selective laser melting (SLM) and direct metal laser melting (DMLM). In the current setting, DMLM has been found advantageous.

To illustrate an example of an additive manufacturing process, <FIG> shows a schematic/block view of an illustrative computerized additive manufacturing system <NUM> for generating an object <NUM>. In this example, system <NUM> is arranged for DMLM. It is understood that the general teachings of the disclosure are equally applicable to other forms of additive manufacturing. Object <NUM> is illustrated as a double walled turbine element; however, it is understood that the additive manufacturing process can be readily adapted to manufacture blade <NUM> and/or shim <NUM> (<FIG>). AM system <NUM> generally includes a computerized additive manufacturing (AM) control system <NUM> and an AM printer <NUM>. AM system <NUM>, as will be described, executes code <NUM> that includes a set of computer-executable instructions defining blade <NUM> and/or shim <NUM> (<FIG>) to physically generate the object using AM printer <NUM>. Each AM process may use different raw materials in the form of, for example, fine-grain powder, liquid (e.g., polymers), sheet, etc., a stock of which may be held in a chamber <NUM> of AM printer <NUM>. In the instant case, blade <NUM> and/or shim <NUM> (<FIG>) may be made of plastic/polymers or similar materials. As illustrated, an applicator <NUM> may create a thin layer of raw material <NUM> spread out as the blank canvas from which each successive slice of the final object will be created. In other cases, applicator <NUM> may directly apply or print the next layer onto a previous layer as defined by code <NUM>, e.g., where the material is a polymer. In the example shown, a laser or electron beam <NUM> fuses particles for each slice, as defined by code <NUM>, but this may not be necessary where a quick setting liquid plastic/polymer is employed. Various parts of AM printer <NUM> may move to accommodate the addition of each new layer, e.g., a build platform <NUM> may lower and/or chamber <NUM> and/or applicator <NUM> may rise after each layer.

AM control system <NUM> is shown implemented on computer <NUM> as computer program code. To this extent, computer <NUM> is shown including a memory <NUM>, a processor <NUM>, an input/output (I/O) interface <NUM>, and a bus <NUM>. Further, computer <NUM> is shown in communication with an external I/O device/resource <NUM> and a storage system <NUM>. In general, processor <NUM> executes computer program code, such as AM control system <NUM>, that is stored in memory <NUM> and/or storage system <NUM> under instructions from code <NUM> representative of blade <NUM> and/or shim <NUM> (<FIG>), described herein. While executing computer program code, processor <NUM> can read and/or write data to/from memory <NUM>, storage system <NUM>, I/O device <NUM> and/or AM printer <NUM>. Bus <NUM> provides a communication link between each of the components in computer <NUM>, and I/O device <NUM> can comprise any device that enables a user to interact with computer <NUM> (e.g., keyboard, pointing device, display, etc.). Computer <NUM> is only representative of various possible combinations of hardware and software. For example, processor <NUM> may comprise a single processing unit, or be distributed across one or more processing units in one or more locations, e.g., on a client and server. Similarly, memory <NUM> and/or storage system <NUM> may reside at one or more physical locations. Memory <NUM> and/or storage system <NUM> can comprise any combination of various types of non-transitory computer readable storage medium including magnetic media, optical media, random access memory (RAM), read only memory (ROM), etc. Computer <NUM> can comprise any type of computing device such as a network server, a desktop computer, a laptop, a handheld device, a mobile phone, a pager, a personal data assistant, etc..

Additive manufacturing processes begin with a non-transitory computer readable storage medium (e.g., memory <NUM>, storage system <NUM>, etc.) storing code <NUM> representative of blade <NUM> and/or shim <NUM> (<FIG>). As noted, code <NUM> includes a set of computer-executable instructions defining outer electrode that can be used to physically generate the tip, upon execution of the code by system <NUM>. For example, code <NUM> may include a precisely defined 3D model of outer electrode and can be generated from any of a large variety of well-known computer aided design (CAD) software systems such as AutoCAD®, TurboCAD®, DesignCAD 3D Max, etc. In this regard, code <NUM> can take any now known or later developed file format. For example, code <NUM> may be in the Standard Tessellation Language (STL) which was created for stereolithography CAD programs of 3D Systems, or an additive manufacturing file (AMF), which is an American Society of Mechanical Engineers (ASME) standard that is an extensible markup-language (XML) based format designed to allow any CAD software to describe the shape and composition of any three-dimensional object to be fabricated on any AM printer. Code <NUM> may be translated between different formats, converted into a set of data signals and transmitted, received as a set of data signals and converted to code, stored, etc., as necessary. Code <NUM> may be an input to system <NUM> and may come from a part designer, an intellectual property (IP) provider, a design company, the operator or owner of system <NUM>, or from other sources. In any event, AM control system <NUM> executes code <NUM>, dividing blade <NUM> and/or shim <NUM> (<FIG>) into a series of thin slices that it assembles using AM printer <NUM> in successive layers of liquid, powder, sheet or other material. In the DMLM example, each layer is melted to the exact geometry defined by code <NUM> and fused to the preceding layer. Subsequently, the blade <NUM> and/or shim <NUM> (<FIG>) may be exposed to any variety of finishing processes, e.g., minor machining, sealing, polishing, assembly to other part of the igniter tip, etc..

<FIG> illustrates a simplified cross-sectional view of the shim placed in the tapered groove of the blade's dovetail <NUM> and the blade attached to the rotor or wheel, according to embodiments of the disclosure. The shim <NUM> is placed in tapered groove <NUM> (not shown for clarity) and the ends of the shim are bent over the rotor <NUM> (or wheel) to lock the shim in place. With both ends of the shim bent over (as shown), the shim is prevented from moving axially (i.e., left or right in <FIG>) with respect to the wheel/rotor <NUM>. The thinned region <NUM> facilitates the bending of this side of the shim, as a full thickness shim may experience cracking if bent ninety degrees. The blended region <NUM> of the rotor <NUM> is important to the bend-over design to keep the bend radius ratio correct for the shim <NUM> to reduce cold-working stress on the shim <NUM>.

<FIG> illustrates a simplified cross-sectional view of the shim <NUM> placed in between the blade dovetail <NUM> and the rotor or wheel, according to embodiments of the disclosure. The shim <NUM> is placed in between the rotor/wheel <NUM> and the blade <NUM> and the ends of the shim are bent over the blade dovetail <NUM> to lock the shim in place. With both ends of the shim bent over (as shown), the shim is prevented from moving axially (i.e., left or right in <FIG>) with respect to the blade. The blade dovetail has the radially lower and axially facing surfaces blended or radiused to reduce stress on the portions of the shim that are bent over. The blended regions <NUM> of the blade dovetail <NUM> is important to the bend-over design to keep the bend radius ratio correct for the shim <NUM> to reduce cold-working stress on the shim <NUM>. It is to be understood that the shim <NUM> may also have one end bent radially upward (against the blade dovetail) and the axially opposing end bent radially downward/inward (against the rotor/wheel). In this variation the corresponding regions of the dovetail and wheel should be radiused or blended to prevent undesired stress on the bent portions of the shim ends.

In various embodiments, components described as being "coupled" to one another can be joined along one or more interfaces. In some embodiments, these interfaces can include junctions between distinct components, and in other cases, these interfaces can include a solidly and/or integrally formed interconnection. That is, in some cases, components that are "coupled" to one another can be simultaneously formed to define a single continuous member. However, in other embodiments, these coupled components can be formed as separate members and be subsequently joined through known processes (e.g., soldering, fastening, ultrasonic welding, bonding). In various embodiments, electronic components described as being "coupled" can be linked via conventional hard-wired and/or wireless means such that these electronic components can communicate data with one another.

Claim 1:
A turbine rotor comprising:
a rotor body (<NUM>) having a plurality of dovetail slots (<NUM>) including a plurality of recesses (<NUM>);
a turbine blade (<NUM>) within one of the plurality of dovetail slots;
a shim (<NUM>) for retaining the turbine blade in the dovetail slots;
the turbine blade having:
a blade (<NUM>) having a first end, (<NUM>) and a second end (<NUM>) opposite the first end;
a tip (<NUM>) at an outer radial portion of the blade; and
a base (<NUM>) at an inner radial portion of the blade, the base including a dovetail (<NUM>) for complementing a corresponding dovetail slot in the turbine rotor, the dovetail having:
a body (<NUM>);
a plurality of projections (<NUM>) extending from the body in opposing directions for complementing a plurality of recesses (<NUM>) in the corresponding dovetail slot; and
a tapered groove (<NUM>) extending through the body from the first end to the second end, the tapered groove having a tapered profile such that a first depth of the tapered groove near the first end is greater than a second depth of the tapered groove near the second end, and wherein the tapered profile gradually transitions from the first depth to the second depth, the tapered groove being open at a bottom surface (<NUM>) of the body and sized to engage the shim and engaging the shim; wherein the shim includes:
a main body (<NUM>) having a first thickness (t<NUM>) measured between an upper surface (<NUM>) and a lower surface (<NUM>); and a second thickness (t<NUM>) measured between the upper surface and the lower surface, the first thickness located near a first end (<NUM>) of the shim and the second thickness located near a second end (<NUM>) of the shim, the first end generally opposing the second end, the first thickness being greater than the second thickness; characterised in
a thinned region (<NUM>) extending from the main body and having a third thickness measured between the upper surface and a thinned, lower surface, the thinned region located at the first end.