Patent Publication Number: US-2022220853-A1

Title: Balancing weight entry port for turbine rotor

Description:
This Application is a Divisional Application of U.S. patent application Ser. No. 17/022,393 filed Sep. 16, 2020, now U.S. patent Ser. No. ______, of which the entire contents thereof are incorporated herein. 
    
    
     TECHNICAL FIELD 
     The disclosure relates generally to turbomachines, and more particularly, to a turbine rotor including a balancing weight entry port for introducing a weight into a balancing weight slot of the turbine rotor, a tool for making the port and a related method. 
     BACKGROUND 
     Certain rotating elements in industrial machines, such as turbine rotors, include balancing weights coupled in a circumferential slot on a circumferential exterior surface of the turbine rotor. The circumferential slot has a cross-sectional shape that includes retaining members, like tabs or ears, that retain one or more weights that have a similar cross-sectional shape. The circumferential slot can have, for example, a dovetail or trapezoidal cross-sectional shape. The weights can be slid along the slot to any circumferential position necessary to balance the turbine rotor, and are fastened in position. In order to introduce the weights to the slot, a balancing weight entry port having a larger axial extent than the slot is milled into the turbine rotor over the slot. The milling typically removes the retaining members of the slot, and provides a position in which the weights can be introduced circumferentially into the slot. One challenge with the balancing weight entry port is that milling of the retaining members of the slot to initially form the entry port can leave circumferentially extending portions (peaks) of the retaining members and sharp corners at the bottom of sidewalls of the port. Each of these structures can lead to the initiation of damage such as cracking in the turbine rotor. Repair of the damage without otherwise damaging the turbine rotor can be very difficult. 
     BRIEF DESCRIPTION 
     A first aspect of the disclosure provides a turbine rotor, comprising: a rotor body; a balancing weight slot defined in an exterior circumference of the rotor body, the balancing weight slot having a first axial width and a first radially outward facing surface at a first radial distance from an axis of the rotor body; and a balancing weight entry port defined in a portion of the exterior circumference of the rotor body and aligned with the balancing weight slot, the balancing weight entry port having a second axial width greater than the first axial width and a second radially outward facing surface at a second radial distance from the axis of the rotor body that is smaller than the first radial distance. 
     A second aspect of the disclosure provides a tool for forming a balancing weight entry port for a balancing weight slot of a rotor body of a turbine rotor, the tool comprising: a motorized machining head; a clamp system configured to couple the motorized machining head to at least a portion of a merge joint flange of the rotor body; a head circumferential positioning system configured to position the motorized machining head in a selected one of a plurality of circumferential positions relative to the balancing weight slot of the rotor body; and a head radial positioning system configured to move the motorized machining head radially relative to the balancing weight slot on the rotor body at each of the plurality of circumferential positions to machine the rotor body, modifying the balancing weight slot. 
     A third aspect of the disclosure provides a method of forming a balancing weight entry port for a balancing weight slot defined in a rotor body of a turbine rotor and extending circumferentially about the rotor body, the method comprising: performing a first plunge machining radially partially into the rotor body, modifying the balancing weight slot at a first circumferential position; and performing one of: a) a circumferential translation after the first plunge machining, and b) performing a second plunge machining radially partially into the rotor body, modifying the balancing weight slot at a second circumferential position different than the first circumferential position, wherein an opening created by the second plunge machining is co-extensive with an opening created by the first plunge machining; and performing a third plunge machining radially partially into the rotor body, modifying the balancing weight slot at a third circumferential position different than the first and second circumferential positions, wherein an opening created by the third plunge machining is co-extensive with openings created by the first and second plunge machining, wherein each plunge machining and the circumferential translation removes a portion of the rotor body within or adjacent the balancing weight slot. 
     The illustrative aspects of the present disclosure are designed to solve the problems herein described and/or other problems not discussed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings that depict various embodiments of the disclosure, in which: 
         FIG. 1  is a schematic illustration of an illustrative gas turbine system; 
         FIG. 2  is a side perspective view of a turbine rotor, according to the prior art; 
         FIG. 3  is an enlarged perspective view of a balancing weight entry port and a balancing weight slot, according to the prior art; 
         FIG. 4  is a cross-sectional view of an illustrative configuration of a balancing weight in a balancing weight slot; 
         FIG. 5  is a front perspective view of a tool positioned on a rotor body for forming a balancing weight entry port, according to embodiments of the disclosure; 
         FIG. 6  is a front perspective view of a tool for forming a balancing weight entry port, according to embodiments of the disclosure; 
         FIG. 7  is a rear perspective view of a tool for forming a balancing weight entry port, according to embodiments of the disclosure; 
         FIG. 8  is a top down view of a member of a head circumferential positioning system, according to embodiments of the disclosure; 
         FIG. 9  is a cross-sectional view of a machining head for machining a balancing weight entry port, according to embodiments of the disclosure; 
         FIG. 10  is a schematic top down view of a rotor body and balancing weight slot with machining steps illustrated by circles representative of a machining head, according to embodiments of the disclosure; 
         FIG. 11  is a schematic cross-sectional view of machining a balancing weight slot to form a balancing weight entry port, according to embodiments of the disclosure; and 
         FIG. 12  is a top down view of a balancing weight entry port, according to embodiments of the disclosure. 
     
    
    
     It is noted that the drawings of the disclosure are not necessarily to scale. The drawings are intended to depict only typical aspects of the disclosure and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings. 
     DETAILED DESCRIPTION 
     As an initial matter, in order to clearly describe the subject matter of the current disclosure, it will become necessary to select certain terminology when referring to and describing relevant machine components within a turbomachine. To the extent possible, common industry terminology will be used and employed in a manner consistent with its accepted meaning. Unless otherwise stated, such terminology should be given a broad interpretation consistent with the context of the present application and the scope of the appended claims. Those of ordinary skill in the art will appreciate that often a particular component may be referred to using several different or overlapping terms. What may be described herein as being a single part may include and be referenced in another context as consisting of multiple components. Alternatively, what may be described herein as including multiple components may be referred to elsewhere as a single part. 
     In addition, several descriptive terms may be used regularly herein, and it should prove helpful to define these terms at the onset of this section. These terms and their definitions, unless stated otherwise, are as follows. As used herein, “downstream” and “upstream” are terms that indicate a direction relative to the flow of a fluid, such as the working fluid through the turbine engine or, for example, the flow of air through the combustor or coolant through one of the turbine&#39;s component systems. The term “downstream” corresponds to the direction of flow of the fluid, and the term “upstream” refers to the direction opposite to the flow (i.e., the direction from which the flow originates). The terms “forward” and “aft,” without any further specificity, refer to directions, with “forward” referring to the front or compressor end of the engine, and “aft” referring to the rearward section of the turbomachine. 
     It is often required to describe parts that are disposed at differing radial positions with regard to a center axis. The term “radial” refers to movement or position perpendicular to an axis. For example, if a first component resides closer to the axis than a second component, it will be stated herein that the first component is “radially inward” or “inboard” of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is “radially outward” or “outboard” of the second component. The term “axial” refers to movement or position parallel to an axis, e.g., of a turbine rotor. Finally, the term “circumferential” refers to movement or position around an axis. It will be appreciated that such terms may be applied in relation to the center axis of the turbine. 
     In addition, several descriptive terms may be used regularly herein, as described below. The terms “first”, “second”, and “third” may be used interchangeably to distinguish one component from another and are not intended to signify position or importance of the individual components. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur or that the subsequently describe component or element may or may not be present, and that the description includes instances where the event occurs, or the component is present and instances where it does not or is not present. 
     Where an element or layer is referred to as being “on,” “engaged to,” “connected to” or “coupled to” another element or layer, it may be directly on, engaged to, connected to, or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
       FIG. 1  is a schematic illustration of an illustrative turbomachine in which a turbine rotor  110 , according to embodiments of the disclosure, may be employed. Here, the turbomachine includes a gas turbine (GT) system  100 . GT system  100  includes a compressor  102  and a combustor  104 . Combustor  104  includes a combustion region  105  and a fuel nozzle assembly  106 . GT system  100  also includes a turbine  108  and a common turbine rotor  110 . In operation, air flows through compressor  102  and compressed air is supplied to combustor  104 . Specifically, the compressed air is supplied to fuel nozzle assembly  106  that is integral to combustor  104 . Assembly  106  is in flow communication with combustion region  105 . Fuel nozzle assembly  106  is also in flow communication with a fuel source (not shown in  FIG. 1 ) and channels fuel and air to combustion region  105 . Combustor  104  ignites and combusts fuel. Combustor  104  is in flow communication with turbine  108  for which gas stream thermal energy is converted to mechanical rotational energy. Turbine  108  includes a number of stages of rotatable blades coupled to the turbine rotor  110 , and rotatably drives turbine rotor  110 . Compressor  102  also is rotatably coupled to turbine rotor  110 . The present disclosure is not limited to any one particular GT system and may be used in connection with any GT system including, for example, any HA, F, B, LM, GT, TM and E-class engine models of General Electric Company, Greenville, S.C., and engine models of other companies. Further, the teachings of the disclosure are not limited to turbomachines in the form of gas turbine systems, and can be applied to any rotating element or rotor that includes a balancing slot and requires balancing. 
       FIG. 2  shows a side view of turbine rotor  110  with any turbine blades/stages removed therefrom. Turbine rotor  110  may include a rotor body  112  in the form of a generally cylindrical shaft, which may have a number of blade stages  114  ( FIG. 1  only) (for compressor  102  and/or turbine  108 ) coupled thereto. Turbine rotor  110  may exhibit asymmetries in its mass distribution, i.e., imbalances. The imbalances may cause turbine rotor  110  to experience periodic forces and torques such as vertical and lateral vibrations, which may also cause the rotor to oscillate during use—similar to an unbalanced tire on a motor vehicle. To address this situation, as shown in  FIG. 2  and the enlarged perspective view of  FIG. 3 , one or more balancing weights  120  are coupled at one or more circumferential positions in a circumferentially extending, balancing weight slot  122  (two shown in  FIG. 2 ) in rotor body  112  of turbine rotor  110  to balance the rotor, and allow it to rotate without oscillation. As shown in one example in the cross-sectional view of  FIG. 4 , balancing weight slot(s)  122  and balancing weight(s)  120  are complementarily configured to retain the balancing weights in the slot. For example, balancing weight slot  122  and balancing weight  120  may have complementary cross-sectional shapes configured to retain balancing weights  120  therein. In one non-limiting example, shown in  FIG. 4 , balancing weights  120  and balancing weight slot  122  have complementary trapezoidal cross-sectional shapes. Here, balancing weight slot  122  includes opposing retaining members  124  in the form of ears or tabs. A fastener  125  such as a set screw may be used to lock balancing weights  120  in position. 
     In order for balancing weight(s)  120  to be introduced into balancing weight slot  122 , rotor body  112  includes one or more balancing weight entry ports  126 . Each balancing weight entry port  126  includes an axially enlarged area of balancing weight slot  122  in which balancing weights  120  can be positioned in, and circumferentially slid into, the slot. As shown in the enlarged perspective view of  FIG. 3 , a balancing weight entry port  126  may be formed, e.g., by machining retaining members  124  from slot  122 , creating port  126  but leaving peaks  128 . During use, the peaks and/or sharp corners  130  where a vertical sidewall  132  of port  126  meets a radially outward facing surface  134  of slot  122  (sharp corners—with a radius of less than 0.76 mm), can crack. The cracks can propagate in rotor body  112 . Accordingly, the peaks and sharp corners should be avoided during initial manufacture, and may need to be removed during servicing. 
     As indicated above, the disclosure provides a turbine rotor including a rotor body, and a balancing weight slot defined in an exterior circumference of the body. The balancing weight slot has a first axial width and a first radially outward facing surface at a first radial distance from an axis of the rotor. The rotor also includes a balancing weight entry port defined in a portion of the exterior circumference of the rotor body and substantially aligned with the balancing weight slot. The balancing weight entry port has a second axial width greater than the first axial width. The balancing weight slot also has a second radially outward facing surface at a second radial distance from the axis of the rotor body that is smaller than the first radial distance, meaning the entry port extends farther into the rotor body than the slot. Embodiments of the disclosure also include a method and a tool for forming the entry port into the rotor body. The tool can be used to perform a series of plunge machining steps to create the new balancing weight entry port. The method may be applied to a new rotor, or a used rotor to remove peaks  128  ( FIG. 3 ) and/or sharp corners  130  ( FIG. 3 ) initiating from a previously formed entry port that may include cracks or other damage. The new balancing weight entry port has rounded corners to forestall new cracks. 
     Referring to  FIGS. 5-12 , a method and a tool for carrying out the method, according to embodiments of the disclosure, will be described.  FIGS. 5 and 6  show front perspective views of a tool  140  for forming a balancing weight entry port  142  for balancing weight slot  122  of rotor body  112  of turbine rotor  110 .  FIG. 5  shows tool  140  in position on rotor body  112 , and  FIG. 6  shows tool  140  apart from rotor body  112 . Tool  140  includes a motorized machining head  150 . Motorized machining head  150  may include any now known or later developed rotary actuator  152  capable of rotating a machining element  154 , e.g., an electric, pneumatic, or hydraulic motor. In certain embodiments, motorized machining head  150  may also be capable of a single plunge machining with a controlled and limited amount of circumferential translation, thus reducing the number of plunge machining steps required. Machining element  154  will be described herein. Tool  140  also includes a clamp system  156  configured to couple motorized machining head  150  to at least a portion of a merge joint flange  160  of rotor body  112 . As illustrated, merge joint flange  160  may include axially coupled, radially extending merge joint flanges  162 ,  164  of two axially coupled portions  166 ,  168  of rotor body  112 . Clamp system  156  may however couple to one or both flanges  162 ,  164  depending on the disposition of rotor body  112 . For example, where rotor body  112  is separated into portions  166 ,  168 , clamp system  156  may couple to only one of flanges  162 ,  164 . Clamp system  156  may include any now known or later developed system for temporarily affixing motorized machining head  150  to rotor body  112 . In the non-limiting example shown, clamp system  156  includes a first clamp member  170  movably coupled to a second clamp member  172  with one or more guide rails  174  perhaps directing axial movement of the members. Clamp system  156  may also include an actuator  176 , e.g., a manual crank or motorized actuator (shown), for axially moving clamp members  170 ,  172  toward or away from one another. Actuator  176  may include, for example, a motorized worm gear  177  that threadably couples to member  170 ,  172 , and can be rotated to change the axial positions of the members. A large variety of alternative actuators  176  could also be employed, e.g., linear rams, etc. Actuator  176  can be operated to have clamp members  170 ,  172  clamp motorized machining head  150  in position on one or both flanges  162 ,  164  of merge joint flange  160  for machining of rotor body  112 , and can similarly be actuated to release motorized machining head  150  from rotor body  112 . Clamp members  170 ,  172  may include any structure to assist in grasping merge joint flanges  162 ,  164 , e.g., rough surfaces, locking features, etc. 
     Tool  140  may also optionally include at least one tie-down member  180  having a first end  182  configured to mount in balancing weight slot  122  and a second end  184  coupled to clamp system  156 . First end  182  may have any shape configured to be positioned and retained in slot  122 , similarly to balancing weights  120  ( FIG. 4 ), e.g., trapezoidal for trapezoidal slot. For example, first end  182  may be sized and shaped to enter slot  122  and be turned so as to be retained therein, or it may be sized and shaped to enter slot  122  using balancing weight entry port  126  ( FIG. 3 ). Second end  184  may include any mechanism to couple to clamp system  156 . As illustrated, second end  184  may include an adjuster  186  therewith to adjust the radial position of first end  182  thereof; however, adjuster  186  may not be necessary in all cases. Adjuster  186  may include any now known or later developed mechanism to linearly change the position of first end  182  relative to clamp system  156 , e.g., a threaded end and fastener, a clamp, etc. One or more tie downs  180  may be employed. 
       FIG. 7  shows a rear perspective view of certain embodiments of tool  140 . As shown best in  FIG. 7 , tool  140  also includes a head circumferential positioning system  190  configured to position motorized machining head  150  in one of the circumferential positions relative to the balancing weight slot  122  of rotor body  112 , and circumferentially translate motorized machining head  150  relative to balancing weight slot  122  of the rotor body  112 . Head circumferential positioning system  190  may take any form of structure capable of adjusting the circumferential position of motorized machining head  150 , e.g., linear actuator, mechanical adjustment system, etc. In one example shown in  FIG. 7 , positioning system  190  may include a first member  192  fixedly coupled to motorized machining head  150 , e.g., some part of the head, and a second member  194  fixedly coupled to clamp system  156 . Second member  194 , as illustrated, may be part of clamp system  156 , e.g., clamp member  172 , or it may be a separate element coupled to clamp system  156 .  FIG. 8  shows a top down view of second member  194 . First member  192  and second member  194  are slidably coupled. In one non-limiting example, first member  192  may include a projection  196  that slidably rides in a slot  198  in second member  194 . Other arrangements may also be possible, e.g., guide rails, etc. 
     As illustrated best in  FIG. 8 , second member  194  may include a position selecting member  200 A-C for each of the plurality of circumferential positions. The number of possible circumferential positions provided relative to balancing weight slot  122  of rotor body  112  may be user defined depending on the circumferential extent of the desire balancing weight entry port  142 . In certain embodiments, however, at least three positions are possible. First member  192  also may also include a position selector  202  configured for selectively positioning in a selected one of position selecting members  200 A-C of second member  194  to position motorized machining head  150  in the selected one of the plurality of circumferential positions relative to balancing weight slot  122  of rotor body  112 . In one non-limiting example, position selector  202  may include a pin  204  extending through first member  192  and seatable in one of position selecting members  200 A-C. Position selecting member  200 A-C may include openings in second member  194  and may be spaced to create the desired circumferential positions of the head. As will be described further, position selecting members  200 A-C may be spaced at any distance necessary to ensure new entry port  142  circumferentially removes the original entry port using the position selecting members. In an alternative embodiment, position selector  202  may be omitted, and motorized machining head  150  may be capable of a single plunge machining with a controlled and limited amount of circumferential translation dictated by a length of slot  198 , thus reducing the number of plunge machining steps required. Here, machining element  154  may be plunged once and then circumferentially translated as projection  196  of first member  192  slidably rides in slot  198  in second member  194 , to provide a limited and controlled circumferential movement of machining element  154  to create entry port  142 . 
     Referring to  FIGS. 5 and 6 , tool  140  also includes a head radial positioning system  210  configured to move motorized machining head  150  radially relative to balancing weight slot  122  on rotor body  112  (vertically as shown on page). The radial movement can be carried out at each of the plurality of circumferential positions to machine rotor body  112 , modifying balancing weight slot  122  ( FIG. 3 ), and creating balancing weight entry port  142 . Head radial positioning system  210  may include any form of a linear actuator  212 , e.g., manual crank, an electric, pneumatic, or hydraulic ram. Head radial positioning system  210  is fixed to clamp system  156 . 
     Machining element  154  is configured to form balancing weight entry port  142  in rotor body  112  relative to balancing weight slot  122 . Machining element  154  may be used to form balancing weight entry port  142  in a slot during manufacture of rotor body  112 . Alternatively, machining element  154  may be used to replace and repair a previously formed balancing weight entry port  126  ( FIG. 3 ). In the latter case, machining element  154  is sized larger than the previously formed balancing weight entry port  126  ( FIG. 3 ) so as to remove additional axial portions of rotor body  112  and remove any damage such as cracks or other damage in peaks  128  or sharp corner(s)  130 . Machining element  154  may include any form of rotary machining element capable of forming the structure described herein. In non-limiting examples, machining element  154  may include a milling head, drill bit, grinding head, etc.  FIG. 9  shows a cross-sectional view of an illustrative machining element  154  according to embodiments of the disclosure. Machining element  154  may have a circular cross-section (see e.g.,  FIG. 5 ) with rounded corners  220  between radial sidewalls  222  and a machining face  223 . Rounded corners  220  are configured to create rounded corners  236  ( FIG. 11 ) (fillet) for balancing weight entry port  142 , i.e., between a radially outward facing surface  232  ( FIG. 11 ) and sidewalls  228  ( FIG. 11 ) thereof. The radius may be user defined to remove any damage such as cracking present, and/or to prevent any additional cracking. In certain illustrative embodiments, rounded corners  220  may have a radius R in a range of 1.250 millimeters (mm) to 5.080 mm. Other ranges may also be possible depending, for example, on the size of rotor body  112  and slot  122 . 
     Tool  140  may be used to form balancing weight entry port  142  for balancing weight slot  122  defined in rotor body  112  of turbine rotor  110 , in accordance with embodiments of a method of the disclosure.  FIG. 10  shows a schematic top down view of rotor body  112  and slot  122  with machining steps illustrated by circles representative of machining element  154 .  FIG. 11  shows a schematic cross-sectional of the machining of balancing weight slot  122 , according to various embodiments. For reference purposes,  FIG. 11  shows a remaining circumferential face of retaining members  124  of slot  122 . As will be recognized, machining element  154  may be used to create balancing weight entry port  142  according to embodiments of the disclosure by removing, among other structure(s), retaining members  124  of slot  122  at any desired circumferential location (into or out of page).  FIG. 11  also shows a previously existing balancing weight entry port  226  in phantom, including sidewalls  132  meeting at sharp corners  130  with a first radially outward facing surface  134  of balancing weight slot  122 . As will be described, tool  140  may be used to expand previously formed balancing weight entry port  126  to create new entry port  142 . In one non-limiting example, new entry port  142  may be 0.050 mm to 2.540 mm larger on each side; other ranges may also be possible depending on size of rotor body  112  and/or slot  122 . 
     In operation, tool  140  is positioned on rotor body  112  in a desired circumferential position to create balancing weight entry port  142  by clamping to one or more flanges  162 ,  164 , i.e., either for a new port or to replace an existing port  126  ( FIG. 3 ). Head circumferential positioning system  190  is set in a first circumferential position, e.g.,  200 A, as described. Head radial positioning system  210  is used to perform a number of plunge machinings to create balancing weight entry port  142 . Each machining uses circular machining element  154 . For purposes of description, and as noted, embodiments of the description use three circumferentially spaced positions  200 A-C to perform three machining steps PM 1 -PM 3  ( FIG. 10 ) to create entry port  142 ; however, more or less than three may be employed. (Note, second plunge machining PM 2  is shown in phantom in  FIG. 10  for differentiation purposes with the other machinings PM 1 , PM 3 ). As shown in  FIGS. 5 and 10 , tool  140  may be coupled to one or more flanges  162 ,  164  such that each machining element  154  is positioned axially relative to rotor body  112  (e.g., by clamp system  156 ) in a range of 0 millimeters (mm) to 0.762 mm from a center (CL) of balancing weight slot  122 . It is noted that other ranges may be possible depending on size of rotor body  112  and/or slot  122 . 
     As shown in  FIG. 10 , head radial positioning system  210  is used to perform a first plunge machining PM 1  radially and partially into rotor body  112 , modifying balancing weight slot  122  at first circumferential position  200 A. Head circumferential positioning system  190  is set in a second circumferential position, e.g.,  200 B, by position selector  202  ( FIG. 7 ). Head radial positioning system  210  is used to perform a second plunge machining PM 2  radially and partially into rotor body  112 , again modifying balancing weight slot  122 , at second circumferential position  200 B. As noted, second circumferential position  200 B is different than first circumferential position  200 A. An opening  230  created by second plunge machining PM 2  is co-extensive with an opening  232  created by first plunge machining PM 1 . Next, head circumferential positioning system  190  is set in a third circumferential position, e.g.,  200 C, by position selector  202  ( FIG. 7 ). Head radial positioning system  210  is used to perform a third plunge machining PM 2  radially and partially into rotor body  112 , again modifying balancing weight slot  122 , at third circumferential position  200 C. As noted, third circumferential position  200 C is different than first and second circumferential positions  200 A,  200 B. An opening  234  created by third plunge machining PM 2  is co-extensive with openings  230 ,  232  created by first and second plunge machinings PM 1 , PM 2 . Each machining, i.e., each circumferential position  200 A-C, may be circumferentially spaced any desired and/or necessary distance from a center of an adjacent machining to collectively create an entry port  142  with the desired circumferential extent, e.g., to completely remove the circumferential extent of the original entry port. As illustrated, each plunge machining PM 1 -PM 3  removes a portion of rotor body  112  within or adjacent balancing weight slot  122 , e.g., retain members  124  and parts of sidewalls  229  of the slot and/or previous slot  126 . As noted, in other embodiments, motorized machining head  150  may be capable of a single plunge machining with a controlled and limited amount of circumferential translation, thus reducing the number of plunge machining steps required. In this case, a single plunge machining may be completed with a circumferential translation of machining element  154  to create the enlarged circumferential entry port  142 . Here, position selector  202  may be omitted, as described. In any event, once complete, any tie-downs  180  may be loosened and removed, and clamp system  156  may be loosened so tool  140  can removed from flange(s)  162 ,  164 . 
     Where used to repair a previously existing balancing weight entry port  126  ( FIGS. 3  and  11 ), the method may include mounting tool  140  using clamp system  156  to at least a portion of merge joint flange  160 , i.e., one or both flanges  162 ,  164 , of a used rotor body  112  that includes a previously existing (first) balancing weight entry port  126  ( FIGS. 3 and 11 ) for balancing weight slot  122 . Advantageously, tool  140  may be used anywhere within a field of use, even with turbine rotor  110  in place in a power plant with a casing removed. The method may include performing a one or more plunge machinings, e.g., first, second and third plunge machinings PM 1 -PM 3 , to modify rotor body  112  to create new (second) balancing weight entry port  142  for balancing weight slot  122  in the same circumferential position as the previously existing balancing weight entry port  126 . Here, previously existing balancing weight entry port  126  has a first axial width W 1  ( FIG. 11 ), and new balancing weight entry port  142  has a second axial width W 2  greater than first axial width W 1 . That is, machining element  154  is wider than first axial width W 1 . Second axial width W 2  may be defined by new sidewalls  228  of new entry port  142 . 
     The plunge machining(s), regardless of whether for a new or used rotor body  112 , also extend into balancing weight slot  122  beyond a first radially outward facing surface  134  thereof, creating a new radially outward facing surface  232 . Consequently, as shown in  FIG. 11 , balancing weight slot  122  has first radially outward facing surface  134  at a first radial distance RD 1  from an axis A (see also,  FIG. 1 ) of rotor body  112 , and entry port  142  with a second radially outward facing surface  238  at a second radial distance RD 2  from axis A of rotor body  112  that is smaller than first radial distance RD 1 . For repair purposes, the deeper radially outward facing surface  232  ensures complete removal of damage such as cracks. A difference between first radial distance RD 1  from axis A of rotor body  112  and second radial distance RD 2  from axis A of rotor body  112  may be in a range of 0.254 millimeters (mm) to 2.286 mm; however, the range may vary depending on, for example, the extent of damage to be removed in a pre-existing entry port  126 . It is noted that balancing weight slot  122  includes sidewalls  229  (formed with retaining members  124 ) extending from slot (first) radially outward facing surface  134  that may be at a non-perpendicular angle α, and new balancing weight entry port  142  has sidewalls  228  extend from new (second) radially outward facing surface  232  at a perpendicular angle ( 3 . Machining element  154  however creates rounded corners  236  coupling new radially outward facing surface  232  and sidewalls  228  of new balancing weight entry port  142 . That is, the machining removes sharp corners  130  and sidewalls  132 , and also any existing peaks  128  ( FIG. 3 ), of previously existing balancing weight entry port  126  that may include cracks or other damage. Sidewall  228  are increased in an axial dimension by machining element  154 . Each sidewall  228  can be increased by as much as 25.4 millimeters (mm) in axial direction, but other ranges may also be possible depending on the size of rotor body  112  and slot  122 . Balancing weight entry port  142  thus provides space for balancing weights  120  ( FIG. 4 ) to be introduced into balancing weight slot  122  in the same manner as the original entry port  126 , but provides rounded corners  236  that act to reduce the creation of cracks in rotor body  112  during subsequent use. Rounded corners  236  may have a radius, for example, in a range of 1.250 millimeters (mm) to 5.080 mm. 
     Referring to  FIGS. 10-12 , a turbine rotor  240  according to embodiments of the disclosure may include rotor body  112 , and balancing weight slot  122  defined in an exterior circumference  244  of rotor body  112 . As shown in  FIG. 11 , balancing weight slot  122  has an axial width W 3  and first radially outward facing surface  134  at first radial distance RD 1  from axis A of rotor body  112 . Rotor body  112  may include first merge joint flange  162  and second merge joint flange  164  axially coupled to the first merge joint flange  162  at a rotor flange interface  250  ( FIG. 10 ). Balancing weight slot  122  may be axially adjacent rotor flange interface  250 ; however other locations are also possible. 
     Turbine rotor  240  also includes balancing weight entry port  142  defined in a portion of exterior circumference  244  of rotor body  112  and aligned with balancing weight slot  122 . Balancing weight entry port  142  has axial width W 2  that is greater than axial width W 3  of slot  122 , thus allowing balancing weights  120  ( FIG. 4 ) to be introduced into the slot at the entry port. Balancing weight entry port  142  also includes a radially outward facing surface  232  ( FIG. 11 ) at radial distance RD 2  from axis A of rotor body  112  that is smaller than radial distance RD 1  of the radially outward facing surface  134  of slot  122 . A difference between radial distance RD 1  of the slot from axis A of rotor body  112  and radial distance RD 2  of entry port  142  from axis A of rotor body  112  may be in the range of 0.254 millimeters (mm) to 2.286 mm. 
     As shown in the top down view of  FIG. 12 , balancing weight entry port  142  includes an interface  252  between radially outward facing surface  134  of slot  122  and radially outward facing surface  232  of port  142 . Interface  252  is rounded, i.e., with the same radius as rounded corners  236  due to the rounded corners  220  ( FIG. 9 ) of machining element  154 . Balancing weight slot  122  has a first cross-sectional shape, e.g., trapezoidal, and balancing weight entry port  142  has a cross-sectional shape different than the first cross-sectional shape of the slot e.g., rectangular with rounded corners  236 . Balancing weight slot  122  includes sidewalls  229  ( FIG. 11 ) that may extend from radially outward facing surface  134  of the slot at a non-perpendicular angle α. In contrast, balancing weight entry port  142  has sidewalls  228  extending from radially outward facing surface  232  of the port at a perpendicular angle β. As noted, entry port  142  includes rounded corner  236  coupling second radially outward facing surface  232  and sidewalls  228  of the balancing weight entry port. Rounded corner  236  may have a radius in a range of 1.250 millimeters (mm) to 5.080 mm; however, other ranges may be possible depending on size of rotor body  112  and/or slot  122 . 
     Embodiments of the disclosure provide a turbine rotor having an entry port with rounded corners to prevent damage such as cracking. The entry port also extends farther into the rotor body to reduce damage. The method and tool according to embodiments of the disclosure allow formation of the entry port in new or used rotor bodies. Where applied to used rotor bodies, formation of the new entry port can remove damage from the rotor body. The tool and method can be advantageously employed in a manufacturing location or in the field. 
     The foregoing describes and shows the processing associated according to several embodiments of this disclosure. It should be noted that in some alternative implementations, the acts noted in the drawings or text may occur out of the order noted or, for example, may in fact be executed substantially concurrently or in the reverse order, depending upon the act involved. Also, one of ordinary skill in the art will recognize that additional steps, e.g., machining or finishing steps, may be added. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” “approximately” and “substantially,” are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged; such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. “Approximately,” as applied to a particular value of a range, applies to both end values and, unless otherwise dependent on the precision of the instrument measuring the value, may indicate+/−10% of the stated value(s). 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.