Abstract:
A balance test indexing tool for use in a balance testing machine to assist a user in testing unbalance in a rotor. The tool includes a rotor mount that is temporarily affixed to the rotor being tested. The tool also includes a rotor mount receiver configured to receive the rotor mount and the rotor in the balance testing machine. The rotor mount and rotor mount receiver are configured to provide an indexing coupling that allows the rotor to be readily indexed to any of a plurality of index positions for unbalance testing in the testing machine. The tool allows multiple balancing runs to be made with relatively little effort needed to re-index the rotor. In some embodiments the tool includes a kinematic coupling that provides highly accurate and repeatable indexing.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims the benefit of priority of U.S. Patent Application No. 61/249,710, filed on Oct. 8, 2009, and titled “Balance Test Indexing Tool for Balance-Testing a Rotor,” which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to the field of balance testing of rotating parts. In particular, the present invention is directed to a balance test indexing tool for balance testing a rotor. 
       BACKGROUND 
       [0003]    Rotors of many types of rotational machinery need to be balanced to ensure smooth operation and longevity. For example, turbine and compressor rotors of gas turbines and impellers of pumps require balancing to correct any unbalance as part of initial manufacturing and often in connection with periodic maintenance. These rotors can span a broad range of sizes and weights, and those that are very large, for example, weighing hundreds to thousands of pounds, can make balance testing and balance correction challenging, time consuming and expensive. 
       SUMMARY OF THE DISCLOSURE 
       [0004]    In one implementation, the present disclosure is directed to a system. The system includes: a balance test indexing tool for assisting with balance-testing a rotor of machinery using a balance testing machine having a drive mechanism, the balance test indexing tool including: a rotor mount configured to be fixedly secured to the rotor; and a rotor mount receiver configured to be coupled between the drive mechanism of the balance testing machine and the rotor mount; wherein the rotor mount and the rotor mount receiver cooperate with one another to provide an indexing coupling between the drive mechanism and the rotor when the rotor, the rotor mount and the rotor mount receiver are installed in the balance testing machine. 
         [0005]    In another implementation, the present disclosure is directed to a system. The system includes: a modular balance test indexing tool system for assisting with balancing a rotor of machinery on a balance testing machine having a drive mechanism, the modular balance test indexing tool system including: a rotor mount configured to be fixedly secured to the rotor; a balance testing machine arbor configured to be coupled between the drive mechanism of the balance testing machine and the rotor mount, wherein the rotor mount and the balance testing machine arbor cooperate with one another to provide a first indexing coupling between the drive mechanism and the rotor when the rotor, the rotor mount and the arbor are installed in the balance testing machine; and a balancing simulator configured to be coupled between the drive mechanism of the balance testing machine and the rotor mount, wherein the rotor mount and the balancing simulator cooperate with one another to provide a second indexing coupling between the drive mechanism and the rotor. 
         [0006]    In still another implementation, the present disclosure is directed to a system. The system includes: a balance testing machine having a drive mechanism; a rotor for a piece of machinery, the rotor being installed in the balance testing machine; a balance test indexing tool for assisting with balance testing the rotor in the balance testing machine, the balance test indexing tool coupled between the drive mechanism and the rotor and including: a rotor mount fixedly secured to the rotor; and a rotor mount receiver coupled between the drive mechanism and the rotor mount; wherein the rotor mount and the rotor mount receiver cooperate with one another to provide an indexing coupling between the drive mechanism and the rotor. 
         [0007]    In yet another implementation, the present disclosure is directed to a method. The method includes: providing a rotor of a piece of machinery; fixedly securing a rotor mount to the rotor so as to form an assembly; and coupling the rotor mount to a rotor mount receiver so as to form an indexing coupling between the rotor and the rotor mount receiver. 
         [0008]    In still yet another implementation, the present disclosure is directed to a method. The method includes: providing a balance testing machine; providing a rotor of a piece of machinery; providing a balance test indexing tool; setting the rotor at a first index position using the balance test indexing tool; operating the balance testing machine to spin the balance test indexing tool and the rotor so as to test the rotor for unbalance at the first index position; setting the rotor at a second index position, different from the first index position, using the indexing tool; and operating the balance testing machine to spin the balance test indexing tool and the rotor so as to test the rotor for unbalance at the second index position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: 
           [0010]      FIG. 1  is a side elevational view of a balance test indexing tool incorporated into a balancing system for testing unbalance of a rotor; 
           [0011]      FIG. 2  is longitudinal cross-sectional isometric view of a rotor and a balance test indexing tool engaged with the rotor; 
           [0012]      FIG. 3  contains enlarged axial views of the rotor mount and rotor mount receiver of  FIG. 2  showing their kinematic coupling features; 
           [0013]      FIG. 4  is a longitudinal cross-sectional isometric view of another rotor and another balancing index tool engaged with the rotor; 
           [0014]      FIG. 5  contains enlarged axial views of the rotor mount and rotor mount receiver of  FIG. 4  showing their kinematic coupling features; 
           [0015]      FIG. 6  is a diagram illustrating a modularized balance test indexing tool system having interchangeable components; 
           [0016]      FIG. 7  is a partial cross-sectional isometric view of a test assembly that includes a balance test indexing tool having indexing indicia; 
           [0017]      FIG. 8A  is a top view of a balancing system showing the rotor indexed to 0° index position of the indexing tool;  FIG. 8B  is a top view of the balancing system of  FIG. 8A  showing the rotor indexed to 120° index position of the indexing tool;  FIG. 8C  is a top view of the balancing system of  FIGS. 8A-B  showing the rotor indexed to 240° index position of the indexing tool; and 
           [0018]      FIG. 9  is a flow diagram illustrating an exemplary balancing process using the balancing system of  FIGS. 8A-C . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Referring now to the drawings,  FIG. 1  illustrates a balance test indexing tool  100  in the context of an overall balancing system  104  in which a rotor  108  is being tested for unbalance using a balance testing machine  112 . As will be described below in detail, tool  100  allows a user to readily and accurately set, or index, rotor  108  to differing index positions throughout a testing procedure, as well as to achieve very high repeatability, in terms of precision, for all of the index positions. As those skilled in the art will readily appreciate after reading this entire disclosure, use of tool  100  can significantly reduce the time it takes not only to perform unbalance testing, but also to correct any unbalance in a rotor, such as rotor  108 . For example, during testing, rotor  108  can be readily re-indexed from a current index position to a new index position without the need to remove and re-fix an arbor to the rotor, as is typically done in conventional processes. As another example, after unbalance in rotor  108  is detected using tool  100  and after the rotor is modified to correct the unbalance, the rotor can be reinstalled and precisely indexed, using the tool, to the index positions used during an earlier test. Thus, another balancing test can be performed with very high repeatability of the indexing. Examples illustrating these and other features of a balance test indexing tool of the present disclosure, such as tool  100 , are described below. First, however, other components of system  104  are further described for context. 
         [0020]    As those skilled in the art will readily appreciate, rotor  108  can be any one of a vast variety of rotating structures, such as a compressor, turbine, or component thereof (e.g., a blade assembly) of a gas turbine (e.g., a jet engine), an impeller of a pump, a flywheel, and virtually any other rotating structure of a piece machinery that can be negatively impacted by the rotor being unbalanced during operation. Consequently, as used herein and in the appended claims, the term “rotor” shall mean a body that is a component of an assembly or the assembly itself designed to rotate when in service and that, during the process of balancing the rotor, may require special tooling to adapt it to a balancing machine. While balance test indexing tool  100  can be adapted for use with virtually any size and weight of rotor  108 , it can be particularly beneficial for rotors where, because of their weight, geometry, repair/replacement costs, traditional balancing methods increase risk. 
         [0021]    Balance testing machine  112  can be virtually any machine suitable for balance testing rotor  108 , such as a conventional balance testing machine. Examples of standards for balancing-machine and balance-testing standards for the aerospace industry include the aerospace recommended practices (ARP) of the Society of Automotive Engineers (SAE) SAE ARP 587, SAE ARP 588, SAE ARP 4048 and SAE ARP 4050, among others. Other industries may have similar standards for various types of rotors. Balance testing machine  112  and its use may conform to any one or more of these standards or other practices. Balance testing machine  112  includes a drive mechanism  116  having an output shaft  120  that spins rotor  108  during testing. Drive mechanism  116  can be any suitable drive mechanism, such as a direct-drive variable-speed motor, an electric motor/variable transmission combination, a belt-driven mechanism or a chain-driven mechanism, among others. In this example, output shaft  120  is coupled to a balancing arbor  124 , which in turn is coupled to balance test indexing tool  100 . In other embodiments, output shaft  120  can be coupled directly to tool  100  or to a balancing simulator (not shown) that is coupled between the output shaft and the tool. As those skilled in the art will understand, a balancing simulator is used in some unbalance testing to simulate one or more parts that will rotate with the rotor being tested when the rotor is in the assembled machinery but are not present during testing. A balancing simulator is an attachment of adequate stiffness and of the same dynamic characteristics (center-of-mass, mass, and moments of inertia) as the rotor, or part of the rotor, it replaces. It should be understood that the term “balancing simulator” and like terms used herein and in the appended claims are intended to cover the devices that are also known by other names, such as “PMIs” (Polar Moment Inertia) and “dummy rotors.” 
         [0022]    In this example, tool  100  includes a rotor mount  128  and a rotor mount receiver  132 . Rotor mount  128  is fixedly secured to rotor  108  using any suitable fixing technique, such as shrink fitting the rotor onto the rotor mount to create a tight friction fit or using hydraulically actuated segments integrated into the rotor mount, among others. Importantly, and as described below in more detail, rotor mount  128  can remain in fixed engagement with rotor  108  during multi-index testing and/or during testing and retesting sequences. In this example, rotor mount receiver  132  is fixedly secured to balancing arbor  124  and rotor  108  has a central aperture (not shown) that receives a spindle (not shown) when the rotor is assembled into the finished machinery. To accommodate this configuration of rotor  108 , rotor mount receiver  132  includes a through-shaft  136  that extends through the rotor&#39;s central aperture and engages a corresponding rotational bearing  140  on balance testing machine  112 . Rotor  108  is supported on its opposite side by rotational bearing  144  on balance testing machine  112 . 
         [0023]    Rotor mount  128  and rotor mount receiver  132  are movable relative to one another so that rotor  108  can be indexed at more than one index position relative to the rotor mount receiver. In this example, rotor mount  128  and rotor mount receiver  132  are configured with three index positions located 120° apart from one another. In other embodiments, a balance test indexing tool made in accordance with the present disclosure can have any number of index positions. The index positions can be defined by discrete indexing stops or may not have any stops so as to allow rotor  108  to be indexed to any of an infinite number of index position. In this example, a set of threaded fasteners  148  are used to hold rotor mount  128  and rotor mount receiver  132  into firm engagement with one another so as to secure rotor  108  in its current index position. To change rotor  108  from one index position to another, fasteners  148  are removed, the rotor and rotor mount  128  are rotated to a different index position and the fasteners are reinstalled. Similarly, if rotor  108  is to be removed from balance testing machine  112  before further testing is performed, for example, to modify the rotor, fasteners  148  are removed so that just the rotor and rotor mount  128  can be removed. Rotor  108  (along with rotor mount  128  still fixed to the rotor) and fasteners  148  can then be reinstalled to balance testing machine  112  with the rotor in the desired index position, relative to rotor mount receiver  132 , which can be the same index position it was in before it was removed from the balance testing machine. In other embodiments, other securing means can be used in place of fasteners  148  to suit a particular design. 
         [0024]    As discussed below, rotor mount  128  and rotor mount receiver  132  can be configured to provide a kinematic coupling or a quasi-kinematic coupling between rotor  108  and drive mechanism  116  when the rotor mount and receiver are engaged with one another. As known in the art, a kinematic coupling traditionally provides six points of support that provide exact constraint, i.e., the desired constraint without redundancy. Perhaps most common among kinematic couplings is the 3-ball/3-groove configuration in which one component of the coupling has three “balls” circumferentially spaced 180° center-to-center and the other component has three corresponding radial grooves also circumferentially spaced 180° center-to-center. When the balls are seated in the corresponding respective grooves, exactly six points of contact exist between the balls and sidewalls of the grooves. It is noted that while the one set of features is traditionally called “balls” because they are often spherical in shape, similar features of other shapes, such as frusto-conical, elipsoidal, etc. are also commonly referred to as “balls.” Therefore, the use of the term “balls” throughout this disclosure and in the appended claims in the context of kinematic couplings is intended to cover all shapes of such like-function features. Kinematic couplings provide sub-micron alignment accuracy and very high alignment repeatability. An example of a kinematic coupling suitable for use in a balance test indexing tool of the present disclosure, such as tool  100 , can be found in U.S. Pat. No. 6,746,172 to Culpepper, titled “Apparatus And Method For Accurate, Precise, And Adjustable Kinematic Coupling,” which is incorporated by reference herein for its teachings on kinematic couplings. 
         [0025]    Quasi-kinematic couplings are very similar to kinematic couplings, but use arc-shaped contact regions rather than point contacts. These arc-shaped regions provide somewhat less defined constraints, but properly designed quasi-kinematic couplings can provide sub-micron alignment accuracy and very high alignment repeatability, just like exact-constraint kinematic couplings. Further details of kinematic and quasi-kinematic couplings can be found in M. L. Culpepper, “Design of quasi-kinematic couplings,”  Precision Engineering  28 (2004) 338-357, which is incorporated herein by reference for its teachings on kinematic and quasi-kinematic couplings. Because of the similarities between kinematic and quasi-kinematic couplings, from this point on and in the appended claims and abstract the term “kinematic coupling” is intended to cover kinematic and quasi-kinematic couplings. Several detailed examples of balance test indexing tools incorporating kinematic couplings are described below. 
         [0026]    Referring now to  FIGS. 2 and 3 , these figures illustrate a balance test indexing tool  200  suitable for use with a “half-shaft” (or “stub shaft”) rotor (with a shaft on only one side of the rotor), such as half-shaft rotor  204  shown in  FIG. 2 . As with rotor  108  of  FIG. 1 , rotor  204  can be a rotor from any of a variety of pieces of machinery. In this example, rotor  204  includes an axle  208  and has a circular groove  212  concentric with the rotational axis  216  of the rotor. Balance test indexing tool  200  includes a rotor mount  220  and a rotor mount receiver  224 . As seen in  FIG. 2 , rotor mount  220  is largely disk-shaped and has a central aperture  228  concentric with rotational axis  216  of rotor  204 . In this example, a cylindrical flange  232  is provided to secure rotor mount  220  to rotor  204  via a friction fit within circular groove  212  in the rotor. As those skilled in the art will readily appreciate, the friction fit can be achieved, for example, using a shrink-fit technique that involves heating (or cooling) one or the other of rotor mount  220  and rotor  204  relative to the other, engaging flange  232  with groove  212  and allowing the two components to reach an equilibrium temperature so that a friction fit is obtained between the flange and sidewall of the groove. 
         [0027]    As best seen in  FIG. 2 , rotor mount receiver  224  includes a half-shaft  236  and an integral coupling portion  240 . Half-shaft  236  cooperates with axle  208  to provide the entire assembly  244  with support points on both sides of rotor  204  for mounting in a balance testing machine, such as balance testing machine  112  of  FIG. 1 , or other balance testing machine. Coupling portion  240  engages rotor mount  220 , in this example, to provide a discrete-indexing-position type indexable coupling. More specifically, in this example rotor mount  220  and coupling portion  240  are configured to provide six index positions for rotor  204  relative to rotor mount receiver  224  using kinematic coupling features. 
         [0028]    Referring now primarily to  FIG. 3 , the kinematic coupling features on rotor mount  220  are three spherical balls  300  spaced circumferentially 120° center-to-center. Coupling portion  240  includes six radial cavities  304  circumferentially spaced 60° center-to-center. Each cavity  304  is associated with a corresponding set of two parallel pins  308  spaced equally from the radial centerline  312  of that cavity. When rotor mount  220  is properly engaged with coupling portion  240  of rotor mount receiver  224 , the three balls  300  engage three corresponding respective ones of the six cavities  304  in a skip pattern and contact each of six corresponding ones of pins  308  at only a single point so as to achieve an exact kinematic constraint condition. As those skilled in the art will readily understand, since balls  300  are spaced at 120° center-to-center and cavities  304  and pin pairs are spaced at 60° center-to-center, the balls can engage the cavities in a manner that provides six index positions at 0°, 60°, 120°, 180°, 240° and 300°. Once a desired index position has been selected and set, rotor mount  220  is firmly drawn into engagement with coupling portion  240  of rotor mount receiver  224  using a pair of bolts  248  (only one is shown in  FIG. 2 , but in this example there are two bolts corresponding to bolt holes  312  in coupling portion  240  in  FIG. 3 ). Rotor mount  224  has six threaded bolt holes  320  for receiving bolts  248  and are located so as to accommodate all six index positions. 
         [0029]      FIGS. 4 and 5  illustrate a balance test indexing tool  400  that has a through-shaft  404  for accommodating a shaftless rotor, such as rotor  408  of  FIG. 4 , which may be a rotor of any of a variety of machines. Referring first to  FIG. 4 , rotor  408  is designed to rotate about rotational axis  412  and includes a central aperture  416  that receives a spindle (not shown) in the assembled machine of which it is part. Tool  400  includes a rotor mount  420  and a rotor mount receiver  424 . Rotor mount  420  has a cylindrical flange  428  that is engaged with rotor  408  via a friction fit within aperture  416  that firmly and fixedly secures the rotor mount to the rotor. This friction fit can be effected using a shrink-fit technique. Alternative ways of fixing rotor mount  420  to rotor  408  include providing flange  428  with hydraulically movable segments that are actuated to firmly engage the inner periphery of aperture  416 . If rotor  408  were to have bolt holes surrounding aperture  416  for connecting the rotor to a flanged mount on a spindle, flange  428  could be eliminated from rotor mount  420  and the rotor could be bolted directly to the rotor mount using, for example, a set of threaded holes that match ones of the bolt holes in the rotor. Other ways of affixing rotor mount  420  to rotor  408  can also be used. 
         [0030]    Rotor mount receiver  424  includes through-shaft  404  and a coupling portion  432  integral with the through-shaft. Through-shaft  404  extends through a central aperture  436  in rotor mount  420  and has a length selected to accommodate the support spacing of the balance testing machine (not shown) in which the assembly  440  will be installed for unbalance testing. Coupling portion  432  may be monolithic with through-shaft  404  or, alternatively, may be formed as a separate component that is subsequently fixed to the through-shaft. In this example, rotor mount  420  and coupling portion  432  of rotor mount receiver  424  include kinematic coupling features that provide tool  400  with six index positions for rotor  408 . 
         [0031]    As seen best in  FIG. 5 , the kinematic coupling features on rotor mount  420  are three spherical balls  500  spaced circumferentially 120° center-to-center. Coupling portion  432  includes three radial V-grooves  504  also circumferentially spaced 120° center-to-center. When rotor mount  420  is properly engaged with coupling portion  432  of rotor mount receiver  424 , the three balls  500  engage corresponding respective ones of V-grooves  504  and contact each of the corresponding side walls  508  at only a single point so as to achieve an exact kinematic constraint condition. As those skilled in the art will readily understand, since balls  500  are spaced at 120° center-to-center and V-grooves  504  are spaced at 120° center-to-center, the balls can engage the V-grooves to provide three index positions at 0°, 120° and 240°. Once a desired index position has been selected and set, rotor mount  420  is firmly biased into engagement with coupling portion  432  of rotor mount receiver  424  using a nut  444  ( FIG. 4 ) threadedly engaged with through-shaft  404 . 
         [0032]      FIG. 6  illustrates a modular balance test indexing tool system  600  that can be useful in minimizing the time for performing balancing operations on a number of rotors (not shown) of differing types and/or configurations. For the sake of illustration, in this example modular system  600  includes four rotor mount receivers  604 ,  608 ,  612 ,  616  and three rotor mounts  620 ,  624 ,  628 . Rotor mount receivers  604 ,  608  are of the simulator type mentioned above in connection with  FIG. 1 , whereas rotor mount receivers  612 ,  616  are of a non-simulator type. As mentioned above, some unbalance testing is performed using a simulator to simulate one or more portions of a finished rotating structure that are not present during testing. Such simulators are configured to match, or nearly match, the rotational characteristics of the not-present portion(s). Consequently, rotor mount receivers  604 ,  608  each have a simulator portion  604 A,  608 A, as well as a shaft stub  604 B,  608 B for engaging a balance testing machine support (not shown) and a coupling portion  604 C,  608 C for coupling that receiver with any one of rotor mounts  620 ,  624 ,  628 . A primary difference between rotor mount receivers  604 ,  608  is that receiver  604  is intended for a half-shaft rotor, whereas receiver  608  is intended for a shaftless rotor. Similarly, rotor mount supports  612 ,  616  are intended for a shaftless rotor and a half-shaft rotor, respectively. As mentioned above, rotor mount supports  612 ,  616  are of the non-simulator type and, so, do not include simulator portions as in supports  604 ,  608 . Consequently, rotor mount receiver  612 ,  616  include a relatively small diameter central shaft  612 A,  616 A suitable for engaging one or more balance testing machine supports and a coupling portion  612 B,  616 B for coupling that receiver with any one of rotor mounts  620 ,  624 ,  628 . Rotor mount receivers  612 ,  616  are suitable for unbalance testing when a simulator is not necessary or desired. 
         [0033]    Rotor mounts  620 ,  624 ,  628  are configured for engaging different rotors. For example, rotor mount  620  includes a cylindrical flange  620 A for engaging, for example, a circular groove in a half-shaft rotor, like rotor mount  220  of  FIG. 2 . Rotor mount  624  includes a hydraulically actuated movable-segment gripper  624 A for gripping, for example, the inner periphery of a central aperture in a shaftless rotor. This situation can be likened to the situation of rotor mount  420  of  FIG. 4 , except that the shrink fit is replaced by the grip by gripper  624 A. It is noted that gripper  624 A can be designed to accommodate apertures of differing diameters so that rotor mount  624  can be used for a variety of rotors without the need for a special mount for each rotor. Rotor mount  628  simply includes threaded fastener holes  628 A for receiving threaded fasteners of a rotor having corresponding bolt holes. Such a rotor could be shaftless or have a half-shaft. 
         [0034]    Each of coupling portions  604 C,  608 C,  612 B,  616 B and each of rotor mounts  620 ,  624 ,  628  includes indexing features that allow each one of rotor mount receivers  604 ,  608 ,  612 ,  616  to couple to each one of the rotor mounts in a manner that provides a balance test indexing tool for each such pair. In the example shown, each coupling portion  604 C,  608 C,  612 B,  616 B includes three balls  604 D,  608 D,  612 C,  616 C (only two visible in each coupling portion) similar to balls  300  of  FIG. 3  and each rotor mount includes six pin-type ball receivers  620 B,  624 B,  628 B (only four indicated in each mount) similar to the configuration of rotor mount  220  as shown in  FIG. 3 . As discussed above in connection with  FIGS. 2 and 3 , this particular configuration of indexing features provides a kinematic coupling having six index positions 60° apart from one another. Of course, these indexing features are merely illustrative, and those skilled in the art will appreciate that other types of features can be used, including features that provide infinite indexing adjustability. Those skilled in the art will also appreciate that the number of and types of rotor mounts and number and types of rotor mounts shown in  FIG. 6  are merely exemplary, and that many other sizes and configurations of these components are possible while maintaining modularity. 
         [0035]      FIG. 7  illustrates a balance test indexing tool  700  that provides indexing in 20° increments. Tool  700  includes a rotor mount  704  and a rotor mount receiver  708 . In this example, rotor mount  704  is similar to rotor mount  420  shown in  FIG. 4 , in that it has a similar cylindrical flange  712  for engaging a rotor, such as rotor  716 . Rotor mount receiver  708  of this example is a bit different from rotor mount receivers  224 ,  424 ,  604 ,  608 ,  612 ,  616  shown in  FIGS. 2-6  in that it is configured as an adapter of sorts for a plain arbor  720 . With this configuration, rotor mount receiver  708  can be fixed to arbor  720  in any suitable manner, such as bolting. Tool  700  includes indexing indicia for assisting a user in selecting and setting up an index position for rotor  716  relative to rotor mount receiver  708 . 
         [0036]    In this example, indexing indicia includes tick marks  724  and angle values  728  on the outer periphery of rotor mount receiver  708  and a corresponding alignment mark  732  on the outer periphery of rotor mount  704 . As those skilled in the art will appreciate, the indexing indicia shown in  FIG. 7  is merely illustrative and other indicia may be used in other embodiments. In addition, the indicia shown can reversed, with tick marks  724  and angle values  728  being located on rotor mount  704  and alignment mark  732  being located on rotor mount receiver  708 . Coupling features on rotor mount  704  and rotor mount receiver  708  include three balls  736  (only one seen in the  FIG. 7  view) and a continuous circular groove  740 , respectively. This allows tool  700  to provide a kinematic coupling with continuously variable adjustability and a high degree of repeatability for a given angular position. In this example, tick marks  724  are provided every 10°. It is noted that in other embodiments having 10° incremented tick marks  724 , tool  700  can be configured to provide discrete indexing, i.e., indexing positions located only at the 10° increments. Other features of tool  700  not described can be similar to like features of balance test indexing tools of  FIGS. 1-6 . The balance test indexing tools of  FIGS. 1-6  can include suitable indexing features in the same or similar manner to the manner just described relative to tool  700 . 
         [0037]      FIGS. 8A-C  and  9  illustrate an example of a method  900  ( FIG. 9 ) of using a balance test indexing tool made in accordance with the present disclosure, such as tool  800  of  FIGS. 8A-C . Before describing method  900 , the context of the method is first provided. Referring to  FIGS. 8A-C , tool  800  is used in a balance testing machine  804  to check rotor  808  for unbalance both before and after the rotor is modified to correct an initially discovered unbalance. Tool  800  in this example is essentially identical to tool  400  of  FIGS. 4 and 5 , except that tool  800  of  FIGS. 8A-C  includes visible indexing indicia in the form of tick marks  812  and angle values  816  on rotor mount receiver  820  at the 0°, 120° and 240° index positions and a corresponding alignment mark  824  on rotor mount  828 . (Note how tool  400  of  FIGS. 4 and 5  includes kinematic coupling features that provide exactly three index positions at 0°, 120° and 240°.) In method  900 , the unbalance testing is performed by collecting unbalance data when rotor  808  is in each of the 0°, 120° and 240° index positions. 
         [0038]    Referring now to  FIG. 9 , and also to  FIGS. 8A-C  as noted, method  900  may begin at step  905  with rotor mount  828  being fixedly secured to rotor  808  to form a mount/rotor assembly  832 . While this can be done in any suitable way, in one example this is accomplished using a shrink fit technique. At step  910 , rotor mount receiver  824  is engaged with mount/rotor assembly  832  with rotor  808  set to the 0° index position ( FIG. 8A ), and nut  836  is installed to firmly bias the mount/rotor assembly against the coupling portion  840  of the rotor mount receiver and to create the test assembly  844 . At step  915 , test assembly  844  is installed into balance testing machine  804 , and at step  920  a balancing run is made with rotor  808  set at the 0° index position. Except for the unique way in which rotor  808  is indexed using a balance test indexing tool made in accordance with the present disclosure, the operation of balance testing machine  804  may be the same as the operation of a balance testing machine in any suitable known balancing process. Therefore, a description of step  920  is not necessary for those skilled in the art to practice method  900 . 
         [0039]    After the balancing run is made with rotor  808  indexed at 0°, at step  925  the rotor is indexed to the 120° index position. This can be accomplished by loosening nut  836 , and rotating mount/rotor assembly  832  relative to rotor mount receiver  820 , in situ, within balance testing machine  804  until alignment mark  824  on rotor mount  828  is aligned, or nearly aligned, with the tick mark  812  corresponding to the 120° index position ( FIG. 8B ). Nut  836  is then re-tightened to firmly bias rotor mount  828  into engagement with coupling portion  840  of rotor mount receiver  820  so as to precisely set the indexing by fully engaging the corresponding respective kinematic coupling features. At step  930 , a balancing run is made with rotor  808  set at the 120° index position. 
         [0040]    After the balancing run is made with rotor  808  indexed at 120°, at step  935  the rotor is indexed to the 240° index position. As before, this can be accomplished by loosening nut  836 , and rotating mount/rotor assembly  832  relative to rotor mount receiver  824 , in situ within balance testing machine  804 , until alignment mark  824  on rotor mount  828  is aligned, or nearly aligned, with the tick mark  812  corresponding to the 240° index position ( FIG. 8C ). Nut  836  is then re-tightened to firmly bias rotor mount  828  into engagement with coupling portion  840  of rotor mount receiver  820  so as to precisely set the indexing by fully engaging the corresponding respective kinematic coupling features. At step  940 , a balancing run is made with rotor set at the 240° index position. 
         [0041]    At step  945 , it is determined whether or not the results of the balancing runs made at each of the 0°, 120° and 240° index positions indicate that rotor  808  passes the unbalance test. As those skilled in the art know, this can be accomplished, for example, by balance testing machine  804  and/or any suitable unbalance analyzer equipment that can analyze the data collected during the test runs at the differing index positions. If it is determined rotor  808  has passed, at step  950  test assembly  844  is removed from balance testing machine  804 , mount/rotor assembly  832  is removed from the test assembly and rotor mount  828  is removed from the rotor. Rotor  808  is now ready to be returned to the manufacturing process of making the machine (not shown) of which the rotor will be a part. 
         [0042]    If at step  945  it is determined that rotor  808  does not pass the unbalance test, at step  955  it is determined what adjustments need to be made to the rotor to correct the unbalance. This can be accomplished using any known techniques, such as using balance testing machine  804  and/or data generated from the balancing runs made in steps  920 ,  930 ,  940 . In this example, it is assumed that the modifications must be made outside of balance testing machine  804 , for example, in a special modifications area of the factory. In addition, in this example, modifications are made while rotor mount  828  remains affixed to rotor  808 . Consequently, at step  960 , test assembly  844  is removed from balance testing machine  804 , mount/rotor assembly  832  is disengaged from rotor mount receiver  820  and the rotor mount assembly is transported to the modifications area. At step  965 , modifications are made to rotor  808  to correct the unbalance. This can be accomplished using known techniques, such as adding material, removing material, changing out one or more components, shifting of components, adding weights, etc. After rotor  808  has been modified, it is then retested by looping back to step  910 . The kinematic coupling of balance test indexing tool  800  permits the retesting to be performed with very high repeatability relative to each preceding unbalance testing of rotor  808 . 
         [0043]    Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.