Patent Publication Number: US-2022236231-A1

Title: Measurement probe edge guide tool

Description:
BACKGROUND 
     The present disclosure relates generally to probes for measuring properties of workpieces or in-service parts and, more specifically, to measurement probes designed to measure properties of marginal portions of workpieces or parts which are bounded by a contoured edge. 
     The traditional method of using an ultrasonic transducer for performing manual hand scans around machined edges involves holding the transducer in a pinch grip between the index finger and thumb, while using the middle finger as a guide against the edge to act as a rail. Existing transducer holders utilize a spring-loaded mechanism, but with a negative protrusion of the transducer that requires the operator to “push” the transducer onto the material within a cage. The cage has a flat contact surface which opens the potential to friction-induced wear and adversely affected performance. The existing tool also has a way to hook onto an edge of the workpiece or part, making it possible for the transducer to lose stability if the cage extends too far off the edge of the workpiece or part. 
     SUMMARY 
     The subject matter disclosed in detail below is directed to a measurement probe edge guide tool that is designed to overcome one or more of the above-described issues associated with an existing probe holder. The measurement probe edge guide tool uses an edge follower comprising two edge contact pins that spin around the outside of the measurement probe using a ball bearing to hug the corner of a contoured edge of the workpiece or in-service part while providing a consistent distance of the center of the probe from the edge. The edge follower enables the tool to inspect the marginal portion bounded by a contoured (machined) edge of a workpiece or part. However, the edge follower is removable so that the tool may also be adapted for use in general acreage inspection. 
     The tool proposed herein features a spring-loaded mechanism with a positive probe protrusion relative to a roller-supported cage, which feature enables the user to push the cage against the surface of the workpiece or part being measured rather than applying force directly to the measurement probe. The spring-loaded mechanism includes a spring chamber-defining part that is affixed to the plastic cage by means of heat-set threaded inserts and bolts. The positive protrusion of the probe (e.g., an ultrasonic transducer) enables the contact portion of the probe (e.g., the delay line of an ultrasonic transducer) to be in constant contact with a normal orientation relative to the plane of the surface being scanned for the duration of the scan without active effort by the user. 
     In accordance with one embodiment, the tool has a handle which is coupled to the cage by means of a universal joint. The universal joint enables the user to reduce wrist and finger strain by reducing the bending of the wrist when going around corners and eliminating the pinch grip associated with using a transducer by itself. The universal joint improves the ergonomics of manual non-destructive inspection of a marginal portion along the contoured edge of a workpiece or part. Besides enhancing safety, the adaptability of the tool proposed herein allows the user to perform scans with one sweeping motion and reduces the amount of time dedicated to readjustment. 
     Although various embodiments of measurement probe edge guide tools are described in some detail below, one or more of those embodiments may be characterized by one or more of the following aspects. 
     One aspect of the subject matter disclosed in detail below is a tool comprising: a cage comprising upper and lower parts and interconnecting structure that connects the upper parts to the lower parts; a measurement probe configured to measure a property of a workpiece or part; a probe retainer configured to retain the measurement probe in a vertical orientation, the probe retainer being translatable relative to the cage in directions parallel to a tool vertical axis; and an edge follower that is rotatable relative to the cage about the tool vertical axis. The edge follower comprises: a ring that encircles a portion of the measurement probe; and first and second edge contact pins that are connected to and project downward from the ring. 
     In accordance with one embodiment, the tool described in the immediately preceding paragraph further comprises: a socket ring affixed to the cage and comprising a plurality of sockets; and a plurality of balls respectively disposed in and protruding from the plurality of sockets. 
     In accordance with one proposed implementation, the ring of the edge follower comprises an inner race having an outer circumferential circular groove, and the tool further comprises: a bearing adapter that is affixed to the cage and comprises an inner circumferential circular groove; and a plurality of rolling elements contained by the inner and outer circumferential circular grooves. 
     In accordance with some embodiments, the tool further comprises: a universal joint comprising a U-joint hub having first and second axes, a first U-joint yoke rotatably coupled to the U-joint hub for rotation about the first axis, and a second U-joint yoke rotatably coupled to the U-joint hub for rotation about the second axis, wherein the second U-joint yoke is affixed to an upper part of the cage; and a handle affixed to the first U-joint yoke. In accordance with other embodiments, the tool further comprises a hand grip affixed to an upper part of the cage. 
     Another aspect of the subject matter disclosed in detail below is a tool comprising: a cage comprising an upper ring, a lower ring, and a plurality of beams connecting the upper ring to the lower ring; a socket ring affixed to the lower ring of the cage and comprising a plurality of sockets; a plurality of balls respectively arranged in the plurality of sockets and protruding below a plane of a bottom surface of the socket ring; a measurement probe having a contact portion; a plunger/retainer subassembly that retains the measurement probe in a central position relative to the cage, the plunger/retainer subassembly being displaceable relative to the cage from a starting position at which the contact portion of the measurement probe projects downward and lower than the cage; a rolling-element bearing comprising inner and outer races and a plurality of rolling elements contained by the inner and outer races, the inner and outer races being disposed between the measurement probe and the lower ring of the cage, the outer race being fixed, and the inner race being rotatable relative to the cage; and first and second edge contact pins that are connected to and project downward from the inner race. The tool user is able to measure properties of (e.g., non-destructively inspect) a marginal portion of a workpiece or in-service part by manually moving the tool while maintaining the edge contact pins in contact with an edge of the workpiece or part. 
     In the alternative, the measurement probe edge guide tool may be reconfigured for general acreage measurement (e.g., inspection) by removing the edge follower. Other aspects of measurement probe edge guide tools are disclosed below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features, functions and advantages discussed in the preceding section may be achieved independently in various embodiments or may be combined in yet other embodiments. Various embodiments will be hereinafter described with reference to drawings for the purpose of illustrating the above-described and other aspects. None of the diagrams are drawn to scale. 
         FIG. 1  is a diagram representing a three-dimensional (3-D) view of a measurement probe edge guide tool equipped with a handle that is mechanically coupled to a cage by means of a universal joint in accordance with one embodiment. 
         FIG. 2  is a diagram representing another 3-D view of the measurement probe edge guide tool depicted in  FIG. 1 , but from a different from a different viewpoint. 
         FIGS. 3 through 6  are diagrams representing side, front, top, and bottom views respectively of the measurement probe edge guide tool depicted in  FIGS. 1 and 2 . 
         FIG. 7  is a diagram representing a cross-sectional view of the measurement probe edge guide tool depicted in  FIGS. 1 and 2 , the section being taken along the plane  7 - 7  indicated in  FIG. 1 , with the exception of the measurement probe which is not sectioned. 
         FIG. 8  is a diagram representing a 3-D view of a rolling cage subassembly included in the measurement probe edge guide tool depicted in  FIGS. 1-7 . 
         FIG. 9  is a diagram representing a 3-D view of the U-joint yoke with spring chamber included in the measurement probe edge guide tool depicted in  FIGS. 1-7 . 
         FIG. 10  is a diagram representing a 3-D view of the U-joint yoke with handle spine included in the measurement probe edge guide tool depicted in  FIGS. 1-7 . 
         FIG. 11  is a diagram representing a 3-D view of the U-joint hub of the universal joint included in the measurement probe edge guide tool depicted in  FIGS. 1-7 . 
         FIG. 12  is a diagram representing a 3-D view of the plunger of the plunger/retainer subassembly included in the measurement probe edge guide tool depicted in  FIGS. 1-7 . 
         FIG. 13  is a diagram representing a 3-D view of the probe retainer of the plunger/retainer subassembly included in the measurement probe edge guide tool depicted in  FIGS. 1-7 . 
         FIG. 13A  is a diagram representing a sectional view of the probe retainer depicted in  FIG. 13 , the section being taken along the plane  13 A- 13 A indicated in  FIG. 13 . 
         FIG. 13B  is a diagram representing a 3-D view of the sectioned probe retainer depicted in  FIG. 13A . 
         FIG. 14  is a diagram representing a 3-D view of the measurement probe included in the measurement probe edge guide tool depicted in  FIGS. 1-7 . 
         FIG. 15  is a diagram representing a 3-D view of the bearing adapter included in the measurement probe edge guide tool depicted in  FIGS. 1-7 . 
         FIG. 15A  is a diagram representing a sectional view of the bearing adapter depicted in  FIG. 15 , the section being taken along the plane  15 A- 15 A indicated in  FIG. 15 . 
         FIG. 15B  is a diagram showing a sectional view of the bearing adapter and a side view of the edge follower included in the measurement probe edge guide tool depicted in  FIGS. 1-7 . 
         FIG. 16  is a diagram representing a 3-D view of the edge follower included in the measurement probe edge guide tool depicted in  FIGS. 1-7 . 
         FIG. 17  is a diagram representing a 3-D view of a measurement probe edge guide tool having two edge contact pins in contact with the edge of a workpiece while a major portion of a rolling cage is seated on the surface of the workpiece and a minor portion of the rolling cage projects beyond the edge of the workpiece. 
         FIG. 18  is a diagram representing a 3-D view of a measurement probe edge guide tool equipped with a hand grip in accordance with another embodiment. 
         FIG. 19  is a diagram representing a cross-sectional view of the measurement probe edge guide tool depicted in  FIG. 18 , the section being taken along the plane  19 - 19  indicated in  FIG. 18 , with the exception of the measurement probe which is not sectioned. 
     
    
    
     Reference will hereinafter be made to the drawings in which similar elements in different drawings bear the same reference numerals. 
     DETAILED DESCRIPTION 
     For the purpose of illustration, measurement probe edge guide tools will now be described in detail. However, not all features of an actual implementation are described in this specification. A person skilled in the art will appreciate that in the development of any such embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
       FIGS. 1 and 2  are diagrams representing three-dimensional (3-D) views from different vantage points of a measurement probe edge guide tool  2  (hereinafter “tool  2 ”) in accordance with one embodiment.  FIGS. 3 through 6  show side, front, top, and bottom views respectively of the tool  2  depicted in  FIGS. 1 and 2 .  FIG. 7  shows a cross-sectional view of tool  2 .  FIG. 8  shows a 3-D view of rolling cage subassembly  3  in isolation. 
     In accordance with the embodiment depicted in  FIGS. 1 and 2 , the tool  2  is equipped with a handle  6  that is mechanically coupled to a rolling cage subassembly  3  by means of a universal joint  8 . The rolling cage subassembly  3  includes a cage  4 . The tool further includes a measurement probe (hidden in  FIG. 1 , but shown in isolation in  FIG. 14 ) which is carried by the rolling cage subassembly  3 . A contact portion  33  of the measurement probe is seen protruding from tool  2  in  FIG. 2 . (As used herein, the term “contact portion” means the portion of the measurement probe that contacts the surface of the workpiece or part during an inspection procedure.) 
     As seen in  FIG. 2 , the tool  2  further includes an edge follower  24  comprising two edge contact pins  30   a  and  30   b  that spin around the outside of the contact portion  33  of the measurement probe to hug the corner of a contoured edge of a workpiece or in-service part. As the edge contact pins  30   a  and  30   b  are pressed against the contoured edge of the workpiece or part, the edge follower  24  rotates about an axis of rotation. (The convention is adopted herein that the axis of rotation of the edge follower  24  is the tool vertical axis  1  which is depicted in  FIG. 7 .) The edge follower  24  enables the tool  2  to inspect a marginal portion of a workpiece or part which extends along a contoured (machined) edge by maintaining the center of the measurement probe at a consistent distance from the edge. 
     As previously mentioned, tool  2  includes a handle  6  which is coupled to the cage  4  by means of a universal joint  8 . Referring again to  FIG. 1 , the universal joint  8  includes a U-joint hub  14 , a first U-joint yoke  10  rotatably coupled to the U-joint hub  14  for rotation about a first axis, and a second U-joint yoke  12  rotatably coupled to the U-joint hub  14  for rotation about a second axis. In one proposed implementation shown in  FIG. 5 , the first and second axes of the U-joint hub  14  are mutually orthogonal. The handle  6  is affixed to the first U-joint yoke  10 . The second U-joint yoke  12  is affixed to the upper part  40  of the cage  4 . Thus, the rolling cage subassembly  3  is rotatable relative to first U-joint yoke  10  about the first and second axes. The universal joint  8  enables the user to reduce wrist and finger strain by reducing the bending of the wrist when going around corners, thereby improving the ergonomics of manual non-destructive inspection of a marginal portion along a contoured edge of a workpiece or part. 
     As best seen in  FIG. 8 , the rolling cage subassembly  3  includes the cage  4  and a socket ring  50  which is affixed to the cage  4 . The cage  4  comprises an upper part  40 , a lower part  44 , and interconnecting structure  42  which connecting the upper part  40  to the lower part  44 . In accordance with the proposed implementation depicted in  FIG. 8 , the upper part  40  and lower part  44  are circular rings, while the interconnecting structure  42  includes four beams. However, a person skilled in the art will appreciate that the upper and lower parts of cage  4  need not be circular. For example, the upper and lower parts of cage  4  may be square. 
     As seen in  FIG. 8 , socket ring  50  is disposed directly underneath and has a geometry that matches the geometry of lower part  44  of cage  4 . The socket ring  50  comprises four mounting brackets  54  which are fastened to cage  4  in four places using heat-set threaded inserts and bolts (not shown in the drawings). The threaded inserts are installed inside bores formed in bosses  25  of cage  4 , which is made of plastic material. The bolts are threadably coupled to the threaded inserts for fastening the socket ring  50  to cage  4 . 
     As seen in  FIG. 2 , the socket ring  50  has a plurality of sockets  38  which receive respective balls (not shown in  FIG. 2 , but see balls  52  in  FIG. 7 ). The rolling cage subassembly  3  is able to move across a surface of a workpiece or part (as depicted in  FIG. 17 ) by rolling on those balls. 
     Referring again to  FIG. 1 , the tool  2  further includes a bearing adapter  5  and a plunger/retainer subassembly  7 . Only portions of the bearing adapter  5  and plunger/retainer subassembly  7  are visible in  FIGS. 1 and 2 . The individual components of bearing adapter  5  and plunger/retainer subassembly  7  are described in detail below with reference to  FIGS. 12-16 . The bearing adapter  5  is affixed to and carried by the rolling cage subassembly  3 . The plunger/retainer subassembly  7  is slidably coupled to the bearing adapter  5  for relative translation up and down along the tool vertical axis. 
     The tool  2  further includes a measurement probe which is not visible in  FIG. 1  because one part of the probe is retained inside plunger/retainer subassembly  7  while another part of the probe is slidable inside the bearing adapter  5 . The measurement probe is held in an upright (vertical) position by the bearing adapter  5  and the plunger/retainer subassembly  7 . The plunger/retainer subassembly  7  includes a probe retainer  18  (shown in isolation in and described in detail below with reference to  FIG. 13 ) that is slidably coupled to bearing adapter  5  in a manner that allows probe retainer  18  to slide in a direction parallel to the tool vertical axis (not indicated in  FIG. 1 , but see tool vertical axis  1  in  FIG. 7 ) while the bearing adapter remains stationary. More specifically, the plunger/retainer subassembly  7  is vertically displaceable relative to bearing adapter  5 . 
     The bearing adapter  5  and the probe retainer  18  are configured to receive respective portions of the measurement probe. The measurement probe is also vertically displaceable relative to the bearing adapter  5  between extended and retracted positions. In the extended position, the contact portion  33  of the measurement probe protrudes from tool  2  as shown in  FIG. 2 . The contact portion  33  is retracted (displaced upward) when tool  2  is placed in contact with the surface of the workpiece. 
     The tool  2  is partially sectioned to reveal the measurement probe  32  in  FIG. 7 . Referring to  FIG. 7 , the bearing adapter  5  includes an upper bearing adapter part  20  and a lower bearing adapter part  20  which are fastened together, while the plunger/retainer subassembly  7  includes a plunger  16  and a probe retainer  18  which are coupled by twist-locking. The probe retainer  18  is slidably coupled to the upper bearing adapter part  20 , which is fixed relative to cage  4 . Thus, plunger  16 , probe retainer  18 , and measurement probe  32  are vertically translatable in tandem along the tool vertical axis. 
     More specifically, the measurement probe  32  is vertically translatable between the extended position seen in  FIG. 7  and a retracted position. The measurement probe  32  is urged toward the extended position by a spring  36  which interacts with plunger  16 . In the extended position seen in  FIG. 7 , the contact portion  33  of measurement probe  32  protrudes below the socket ring  50 . However, when the rolling cage subassembly  3  is placed on a surface, that surface presses against the contact portion  33  of measurement probe  32 , causing measurement probe  32  to retract relative to cage  4  until the end face of contact portion  33  is co-planar with a plane defined by the points of contact of balls  52  on the surface (assuming a planar surface for the sake of simplicity). 
     As best seen in  FIG. 7 , the spring  36  is seated in a spring chamber  35  formed in a lower portion of the second U-joint yoke  12 . The spring chamber  35  communicates with a recess  31 . In one proposed implementation, spring chamber  35  is a circular cylindrical cavity having a first radius, whereas recess  31  is a circular cylindrical cavity having a second radius smaller than the first radius. The recess  31  and spring chamber  35  are separated by an intermediate space bounded by a conical surface. The conical surface guides the end of the shaft of plunger  16  into recess  31  during retraction (upward displacement) of the measurement probe  32 . 
       FIG. 7  also shows a pair of ball bearings  34   a  and  34   b  which rotatably couple the first U-joint yoke  10  to the U-joint hub  14  to enable the first U-joint yoke  10  to rotate about the first axis of rotation. An identical pair of ball bearings (not visible in  FIG. 7 ) enable the second U-joint yoke  12  to rotate about the second axis of rotation. 
       FIG. 9  shows a 3-D view of the second U-joint yoke  12  in accordance with one proposed implementation of tool  2  depicted in  FIGS. 1-7 . The spring chamber  35  shown in  FIG. 7  is not visible in  FIG. 9 . The second U-joint yoke  12  consists of two plastic parts  12   a  and  12   b  which are fastened together using heat-set threaded inserts and bolts. The threaded inserts are installed inside four bores  78  formed in a mounting crosspiece  76 . The four bores  78  align with four bores  41  which are distributed at equiangular intervals around the upper part  40  of cage  4 , as seen in  FIG. 8 . The second U-joint yoke  12  further includes a pair of receptacles  72   a  and  72   b  having respective circular cylindrical cavities  74  (only one of which is visible in  FIG. 9 ). A pair of ball bearings (not shown in  FIG. 9 ) may be press fit into the cavities  74  of receptacles  72   a  and  72   b.    
       FIG. 10  shows a 3-D view of the first U-joint yoke  10 . The first U-joint yoke  10  comprises a pair of yoke arms  56   a  and  56   b  and a handle spine  58  to which the handle  6  shown in  FIG. 1  is attached. The first U-joint yoke  10  further includes a pair of receptacles  60   a  and  60   b  having respective circular cylindrical cavities  62  (only one of which is visible in  FIG. 10 ). The ball bearings  34   a  and  34   b  seen in  FIG. 7  may be press fit into the cavities  62  of receptacles  60   a  and  60   b.    
       FIG. 11  shows a 3-D view of the U-joint hub  14  of the universal joint  8  depicted in  FIG. 1 . The U-joint hub  14  includes a spider  48  and two pairs of trunnions  46   a - 46   d.  The trunnions  46   a - 46   d  may be integrally formed with or attached to respective ends of the spider limbs. In one proposed implementation, trunnions  46   a  and  46   b  share a common first axis, while trunnions  46 c and  46   d  share a common second axis which is orthogonal to the first axis. The trunnions  46   a  and  46   b  may be press fit into ball bearings which are respectively press fit into the cavities  74  of receptacles  72   a  and  72   b  seen in  FIG. 9 . Likewise the trunnions  46 c and  46   d  may be press fit into ball bearings which are respectively press fit into the cavities  62  of receptacles  60   a  and  60   b  seen in  FIG. 10 . 
       FIG. 12  shows a 3-D view of the plunger  16  of the plunger/retainer subassembly  7  included in tool  2 . The plunger  16  has a base  64 , a flange  70 , and a shaft  68 . The base  64  of plunger  16  is seated in an upper cavity formed in the probe retainer  18 . The base  64  has a pair of projections  66   a  and  66   b  which project radially outward. These projections  66   a  and  66   b  enter and sit in respective inner circumferential grooves  83  (see  FIGS. 13A and 13B ) formed in the probe retainer  18 , thereby interlocking plunger  16  and probe retainer  18  so that they displace vertically in tandem. The flange  70  is disposed inside the spring chamber  35  (previously described with reference to  FIG. 7 ). The spring  36  bears against the flange  70  to exert a spring force which urges the plunger  16  downward. However, if an upward force is exerted on plunger  16  which is sufficient to overcome the spring force, then spring  36  is compressed and the tip of shaft  68  of plunger  16  displaces upward and into the recess  31  seen in  FIG. 7 . 
       FIG. 13  shows a 3-D view of the probe retainer  18  in accordance with one proposed implementation. The probe retainer  18  comprises sidewalls  71  and  73  having different outer diameters, the outer diameter of sidewall  71  being greater than the outer diameter of sidewall  73 . The sidewalls  71  and  73  are connected by an offset. The probe retainer  18  has a slot  82  which extends the entire length of sidewall  71  and part of the length of sidewall  73 . The slot  82  provides clearance for a conduit  80  of the measurement probe  32  depicted in  FIG. 14  when the probe retainer  18  is slid onto the uppermost portions of the measurement probe  32  during assembly of tool  2 . 
       FIG. 13A  is a diagram representing a sectional view of the probe retainer depicted in  FIG. 13 , the section being taken along the plane  13 A- 13 A indicated in  FIG. 13 .  FIG. 13B  is a diagram representing a 3-D view of the sectioned probe retainer depicted in  FIG. 13A . As seen in  FIGS. 13A and 13B , the inner surface  77  of sidewall  73  and the inner surface  87  of sidewall  71  form a lower cavity which is configured (sized and shaped) to receive the uppermost portion  37  and mid-portion  39  of measurement probe  32  seen in  FIG. 14 . The section plane bisects a pair of diametrally opposed vertical grooves  81  which communicate with an upper cavity defined by the inner surface  84  of sidewall  73 . The upper cavity is configured to receive the base  64  of plunger  16  seen in  FIG. 12 . The upper and lower cavities are separated by a floor  75 . When the plunger  16  and probe retainer  18  are assembled to form the plunger/retainer subassembly  7 , a bottom surface of the base  64  of plunger  16  rests on the upper surface of the floor  75  of probe retainer  18 . 
     The vertical grooves  81  seen in  FIGS. 13, 13A, and 13B  are configured to receive and guide the projections  66   a  and  66   b  projecting from base  64  of plunger  16  seen in  FIG. 12 . As seen in  FIG. 13A , each vertical groove  81  intersects a respective inner circumferential groove  83 , which allows the projections  66   a  and  66   b  to slide down vertical grooves  81  as plunger  16  is inserted into the upper cavity of probe retainer  18  and then the plunger  16  is twisted so that as base  64  of plunger  16  rotates, the projections  66   a  and  66   b  slide into respective inner circumferential grooves  83 , thereby interlocking the plunger  16  and probe retainer  18  so that these elements displace vertically in tandem. 
       FIG. 14  is a diagram representing a 3-D view of the measurement probe  32  included in tool  2 . The uppermost portion  37  and mid-portion  39  of measurement probe  32  fit inside the above-described lower cavity of probe retainer  18 . The measurement probe  32  is configured to measure (e.g., detect) a property (e.g., an anomaly) of a workpiece or part. A conduit  80  extends radially outward from the uppermost portion  37  of measurement probe  32 . An umbilical cable (not shown in the drawings) is passed through conduit  80  to connect the probe to sources of electric power or liquid couplant. For example, in cases where the measurement probe  32  is an ultrasonic transducer, the umbilical cable may include electrical wires for receiving electrical pulses from and returning ultrasonic inspection data signals to an external device and a hose for supplying water to water columns inside the probe, which water acoustically couples the transducer to the structure being interrogated. In cases where measurement probe  32  is an ultrasonic transducer, the contact portion  33  is a delay line. 
       FIG. 15  shows a 3-D view of the bearing adapter  5  included in tool  2  depicted in  FIGS. 1-7 .  FIG. 15A  is a diagram representing a sectional view of the bearing adapter  5  depicted in  FIG. 15 , the section being taken along the plane  15 A- 15 A indicated in  FIG. 15 . The bearing adapter  5  includes an upper bearing adapter part  20  and a lower bearing adapter part  22 , both made of plastic material. The upper bearing adapter part  20  is affixed to the cage  4 . The lower bearing adapter part  20  is fastened to upper bearing adapter part  20  by means of fasteners not shown in  FIG. 15A . Instead,  FIG. 15A  shows throughholes  98  which extend vertically through the upper bearing adapter part  20  at bosses  85  and throughholes  99  which extend vertically through the lower bearing adapter part  22 . Heat-set threaded inserts may be installed in throughholes  99  of lower bearing adapter part  22  prior to assembly. To assemble the bearing adapter  5 , the lower bearing adapter part  22  is aligned underneath the upper bearing adapter part  20  and then bolts are passed through throughholes  98  and threadably coupled to the threaded inserts. 
     The upper bearing adapter part  20  has a cavity which is configured to receive sidewall  71  of probe retainer  18  and mid-portion  39  of measurement probe  32 . More specifically, the inner surface  86  of upper bearing adapter part  20  surrounds sidewall  71  of probe retainer  18  while a first ledge  89  provides a seat for probe retainer  18 . In addition, the inner surface  93  of upper bearing adapter part  20  surrounds mid-portion  39  of measurement probe  32  while a second ledge  91  provides a seat for measurement probe  32  in the fully extended position where contact portion  33  protrudes as seen in  FIGS. 2 and 7 . The upper bearing adapter part  20  also includes a vertical projection  79  which projects radially inward from inner surface  86  and extends upward from the first ledge  89 . The vertical projection  79  fits inside the slot  82  of probe retainer  18 , which slot is seen in  FIG. 13 . 
     When assembled as shown in  FIG. 15A , the two parts of bearing adapter  5  form an outer race of a ball bearing. More specifically, the upper bearing adapter part  20  has a circumferential surface  90  that forms the upper half of an inner circumferential circular groove, whereas the lower bearing adapter part  20  has a circumferential surface  92  that forms the lower half of the inner circumferential circular groove. In addition, the upper bearing adapter part  20  has a circular cylindrical surface  88  that defines a space that receives an upper flange  27   a  of the inner race  26  of edge follower  24  shown in  FIG. 16 , while the lower bearing adapter part  22  has a circular cylindrical surface  94  that defines a space that receives a lower flange  27   b  of the inner race  26  of edge follower  24 . As shown in  FIG. 16 , the inner race  26  has a central opening  29  (which receives the contact portion  33  of measurement probe  32 ) and an outer circumferential circular groove  28  (which is surrounded by the inner circumferential circular groove formed by circumferential surfaces  90  and  92 ). 
       FIG. 15B  is a diagram showing a sectional view of the bearing adapter  5  and a side view of the edge follower  24  in an assembled state. A plurality of balls  51  are contained by the inner race  26  of edge follower  24  and the outer race of bearing adapter  5 . Thus, the edge follower  24  is able to rotate freely about tool axis  1  (seen in  FIG. 7 ). This free rotation allows the edge contact pins  30   a  and  30   b  to stay in contact with the edge of a workpiece or part being measured (e.g., non-destructively inspected) as depicted in  FIG. 17 . 
       FIG. 17  is a diagram representing a 3-D view of a measurement probe edge guide tool  2  having two edge contact pins  30   a  and  30   b  in contact with the edge  102  of a workpiece  100  while a major portion of the rolling cage assembly  3  is seated on the surface  104  of workpiece  100  and a minor portion of the rolling cage assembly  3  projects beyond the edge  102  of the workpiece  100 . After both edge contact pins  30   a  and  30   b  have been placed in contact with edge  102 , the technician can manipulate the handle  6  to cause the measurement probe  32  to move along a marginal portion of surface  104  which is bounded by edge  102 . As the tool  2  travels over the marginal portion of surface  104 , the technician maintains the edge contact pins  30   a  and  30   b  in contact with the edge  102 , which has the effect of maintaining the center of the measurement probe at a consistent distance from the edge  102 . 
       FIG. 18  is a diagram representing a 3-D view of a measurement probe edge guide tool  2 ′ in accordance with an alternative embodiment. The measurement probe edge guide tool  2 ′ is identical to tool  2  described above except that a hand grip  96  is substituted in place of the handle  6  and universal joint  8 . 
       FIG. 19  is a diagram representing a cross-sectional view of the measurement probe edge guide tool depicted in  FIG. 18 , the section being taken along the plane  19 - 19  indicated in  FIG. 18 , with the exception of the measurement probe  32  which is not sectioned. Instead of the spring chamber  35  being incorporated in the universal joint as described above, in measurement probe edge guide tool  2 ′, the spring chamber  35  is incorporated in the lowermost portion of the hand grip  96 . 
     While measurement probe edge guide tools have been described with reference to various embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the teachings herein. In addition, many modifications may be made to adapt the teachings herein to a particular situation without departing from the scope thereof. Therefore it is intended that the claims not be limited to the particular embodiments disclosed herein. 
     As used in the claims, the terms “upper”, “higher”, “downward”, and “lower” refer to vertical positions of a tool component relative to a tool vertical axis which is oriented normal to a horizontal planar surface when the tool is placed on that horizontal planar surface. As used in the claims, the phrase “connected to” should be construed broadly to encompass “attached to” and “integrally formed with”.