Patent Publication Number: US-11397139-B2

Title: Metallographic grinder and components thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119(e) and the benefit of U.S. Provisional Application No. 62/463,793 entitled METALLOGRAPHIC GRINDER/POLISHER, filed on Feb. 27, 2017, by John Hauck, the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a metallographic specimen preparation apparatus, namely, components of a grinder for preparing a specimen for subsequent analysis. 
     Grinders have been used in metallographic preparation for many years. Typically, the machines include a rotating platen to which an abrasive pad is attached. A rotating head is positioned above the abrasive pad with a holder for positioning and holding specimens on the abrasive pad. In some units, a specimen driver extends downwardly and may include fingers aligned with and positioned above the specimens, which are positioned in a specimen holder to apply pressure to the specimens against the platen as the platen rotates. The specimen driver may rotate the specimen holder in either the same or a direction opposite the platen. 
     Prior art metallographic grinders have employed flat platens and rigid fingers to support the metallographic specimens being finished. The resultant specimens, once polished to a flatness of about 0.002 inch to about 0.004 inch, are analyzed utilizing microscopy, micro hardness testers, or other instruments to determine physical characteristics of specimens which are of interest. With such prior art machines, the flatness of the specimen has proven somewhat inadequate. 
     There exists a need, therefore, for an improved grinder which will provide a much flatter surface to a specimen for subsequent examination and analysis. 
     SUMMARY OF THE INVENTION 
     The present invention satisfies this need by providing a platen for use with a metallographic grinder which improves the flatness of a specimen during grinding. Instead of being flat, the platen has an outer peripheral rim which has a surface-oriented height reduction. When a central force specimen holder is employed, the various platen geometrics provide a vastly improved flatness of the specimen. When an individual force specimen holder is employed, flexible fingers are provided for holding a specimen against an abrasive disk on the platen. The fingers are allowed to move laterally (i.e., wobble) to minimize the tipping forces on the specimen during the grinding process. Either one or both of these improvements results in a much flatter specimen surface for use in subsequent analysis. A platen with a surface-oriented height reduction at the outer edge can be used with either an individual force specimen holder in which the specimens are held down with fingers, or with a central force specimen holder in which the specimens are clamped into place in the specimen holder. With the grinder of the present invention, therefore, improved specimen flatness is achieved to facilitate the subsequent analysis of the specimens. 
     In one embodiment of the invention, a platen is provided for use in a metallographic grinder and an outer peripheral rim with a surface-oriented height reduction. In an embodiment for use with an individual force specimen holder, at least one flexible finger is provided for engaging the specimen to apply a force to the specimen against the platen. The at least one finger allows a specimen within a specimen holder to move laterally to some extent with respect to the specimen holder. 
     In yet another embodiment, a metallographic grinder is provided and includes a base rotatably supporting a generally disk-shaped platen, the platen having an outer peripheral rim with a surface-oriented height reduction. The grinder includes a head assembly positioned above the base and includes a specimen holder for positioning at least one specimen in contact with the platen. In yet another embodiment, the head assembly of a grinder includes at least one flexible finger engaging the specimen to apply a force to the specimen against the platen with surface-oriented height reduction and wherein at least one finger allows a specimen within the specimen holder to move laterally to some extent with respect to the specimen holder. 
     These and other features, objects and advantages of the present invention will become apparent upon reading the following description thereof together with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sequence diagram illustrating from left-to-right the steps of preparing a part in a mount for subsequent grinding; 
         FIG. 2  is a fragmentary perspective view of a grinder embodying the present invention; 
         FIG. 3  is an exploded perspective view of an individual force specimen holder and hub for attaching the specimen holder to the specimen driver shown in  FIG. 2 ; 
         FIG. 3A  is an exploded perspective view of a central force specimen holder and hub for attaching the specimen holder to the driver shown in  FIG. 2 ; 
         FIG. 4  is a top plan view of the individual force specimen holder; 
         FIG. 5  is a side elevational view of the individual force specimen holder; 
         FIG. 6  is a top plan view of a platen employed in the grinder shown in  FIG. 2 ; 
         FIG. 7  is a side elevational view of the platen shown in  FIG. 6 , showing in exploded perspective view an abrasive pad used with the grinder; 
         FIG. 8  is an enlarged fragmentary view of a the circled area of  FIG. 7 , showing a first structure for providing surface-oriented height reduction of the outer peripheral edge of the platen; 
         FIG. 9  is a side elevational view of an alternative structure for surface-oriented height reduction of the platen at the outer periphery; 
         FIG. 10  is an enlarged view of the circled area shown in  FIG. 9 ; 
         FIG. 11  is a side elevational view of an alternative platen illustrating yet another structure for surface-oriented height reduction of the outer periphery of the platen; 
         FIG. 12  is an enlarged view of the circled area shown in  FIG. 11 ; 
         FIG. 13  is a side elevational view of yet another embodiment of the platen in which surface-oriented height reduction of the outer periphery is provided; 
         FIG. 14  is an enlarged fragmentary view of the circled area shown in  FIG. 13 ; 
         FIGS. 15A-15C  are fragmentary vertical cross-sectional views of one of the specimen driver retractable fingers illustrating its lateral movement during the grinding operation; 
         FIG. 15D  is an enlarged cross-sectional view of one of the pads used with the fingers of  FIGS. 15A-15C and 16A-16C ; 
         FIGS. 16A-16C  are fragmentary vertical cross-sectional views of an alternative embodiment of one of the specimen driver retractable fingers illustrating its lateral movement during the grinding operation; 
         FIGS. 17A-17C  are fragmentary vertical cross-sectional views of yet another embodiment of the specimen driver retractable fingers illustrating its lateral movement during the grinding operation; 
         FIG. 17D  is an enlarged fragmentary side elevational view of the finger shown in  FIGS. 17A-17C ; 
         FIGS. 18A-18C  are fragmentary vertical cross-sectional views of a further embodiment of one of the specimen driver retractable fingers illustrating its lateral movement during the grinding operation; and 
         FIGS. 19A-19C  are fragmentary vertical cross-sectional views of a further embodiment of one of the specimen drivers using an inflatable bladder and illustrating its lateral movement during the grinding operation. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to  FIG. 1 , there is shown a four-step sequence (from left to right) of preparing a part, such as a machine bolt for encapsulating into a puck-like mount for use in the grinder of the present invention. The bolt  10  is only an example of one of numerous items on which a company may want to perform a metallographic analysis. In this example, the manufacturer wants to determine the hardness of threads of the bolt. In  FIG. 1 , a machine bolt  10  is shown in its initial form and is first cut in half, as shown at  11 . The machine bolt is then placed in a mounting press  12  which includes upper and lower pistons  13  and  14 , respectively, and a pressure cylinder  15  to allow the part  11 , such as the cutaway bolt, to be encapsulated into a puck-like mount  18  utilizing a thermosetting material, such as phenols, acrylics, epoxies, or other resins typically employed for forming specimen  16 , such as bolt  10 , for analysis. The mount  18 , including the metallographic part, can be formed utilizing a mounting press of the type disclosed in U.S. Pat. No. 7,404,707, the disclosure of which is incorporated herein by reference. The specimen  16  is inverted, as seen on the right side of  FIG. 1 , when removed from cylinder  15  to expose the unfinished surface  17  of the bolt within the mount  18 . 
     Turning now to  FIG. 2 , there is shown a grinder  50  embodying the present invention. 
     The grinder  50  includes a base assembly  20  and a head assembly  40 . The head assembly  40  is vertically movable with respect to the base assembly  20  by means of an interconnecting movable mounting post  25 , which allows vertical movement of the head assembly  40  up and down, as shown by arrow A in  FIG. 2 , with respect to base assembly  20 . A platen  24  is rotatably supported by base assembly  20  and rotatably driven by a motor contained within the base assembly  20  in a conventional manner to rotate at variable speeds in either direction, i.e., either counterclockwise or clockwise, as illustrated by arrow B in  FIG. 2 . The platen  24  can range typically from 8 inches to 12 inches in diameter depending upon a particular machine  50 . The upper surface of the platen  24  is covered by a removable abrasive pad  22  ( FIG. 7 ), which has a lower adhesive or magnetic side  21  to allow its positioning and adhesion to the generally disk-shaped platen  24  and be changed to different grits during the grinding steps. Typically, pad  22  has an upper abrasive surface that ranges from about 60 grit to about 1200 grit, and the grinding process frequently requires three to four replacements for the adhesive pads  22  from a coarser grit (lower number) to a finer grit for final grinding. The movement of head assembly  40  upwardly and away from platen  24  allows easy replacement of the pad  22  as well as positioning the specimen  16  in the specimen holder  30 . The thickness of the abrasive pads  22 , which cover the upper surface of the platens  24 , is about 0.02 inches. This allows the grinding surface  23  of the pad  22  to conform to the shape of the upper surface of the platens  24 . Typically, the platen will generally be disk-shaped as will be the abrasive pad, however, other geometries of the platen and pad may employ the features of these inventions. 
     The head assembly  40  includes a specimen driver  44 , which is generally cylindrical and which is driven by a motor in a conventional manner within head assembly  40  to rotate in either in a clockwise or counterclockwise direction as indicated by arrow C, either in the same direction as platen  24  or in an opposite direction during the grinding process. Typically, the platen  24  is rotated from about 50 to about 600 rpm and preferably about 300 rpm. The specimen driver  44 , on the other hand, typically rotates at a slower speed from about 10 to about 150 rpm and preferably about 75 rpm. 
     A specimen holder  30  is coupled to a hub  32 , as seen in  FIG. 3 , by means of fastening screws  31 , which are threaded into the lower cylindrical end  34  of hub  32 . The hub  32  snap-fits within the specimen driver  44  by means of a snap-fit coupling  36  and suitable interlocking pins (not shown) in specimen driver  44  which engage apertures  35  in hub  32  to rotate specimen holder  30  with driver  44 . The snap-fit coupling  36  allows removal and replacement of specimen holder  30 . This allows different types of specimen holders to be used, such as an individual force specimen holder ( FIGS. 3-5 ) or a central force specimen holder ( FIG. 3A ). The former is the specimen holder  30  of the preferred embodiment which can be disk-shaped and includes six equally spaced (60°) apertures  38  having a diameter of about 1.515 inches for loosely receiving the specimens  16 , which have a diameter of 1.5 inches. Thus, there is 0.015 inch between the inner diameter of apertures  38  and the outer diameter of specimen  16  to allow the specimens to move to some extent within the specimen holder  30  during the grinding process. For specimens ranging in size from about 1 inch to about 2 inches, the gap in diameters between specimens  16  and apertures  38  in the holders would remain about 0.015 inch. This random movement using flexible holding fingers, as disclosed below, improves the flatness of the specimen surfaces  17  ( FIG. 1 ). 
     Specimen holder  30  is shown in detail in  FIGS. 3-5  and includes three apertures  37  which allow fasteners  31  to attach the specimen holder  30  to the hub  32 . The specimen holder is typically 6 inches in diameter as compared to the 8 inch to 12 inch diameter platen  24 . Head assembly  40  positions the specimen holder  30 , spaced above and offset from the axis of rotation of the platen  24 , in a position as seen in  FIG. 2  for the grinding operation. Specimen driver  44  ( FIG. 2 ) includes six flexible fingers  60 - 65  that align with and engage the upper surfaces of specimens  16  captively held by specimen holder  30 . The fingers  60 - 65  may be vertically movable to be retractable within head  44 , as shown by representative arrows D in  FIG. 2 , and may be spring-loaded and which, as described below in connection with  FIGS. 15-19 , engage with the upper surface  19  of specimens  16  to apply a downward force of from about 1 to about 12 pounds and preferably 4 pounds on the surface  17  of specimen  16 , pressing it against the grinding surface  23  of abrasive pad  22  during the grinding process. Specimen holder  30 , in one embodiment, is 6 inches in diameter, made of stainless steel or aluminum, and has a thickness of about 0.075 inch. 
     An alternative central force type specimen holder  130  is shown in  FIG. 3A  and includes a plurality of specimen-holding apertures  138  for holding specimens  16  of the same type previously described above. The holder  130  is a relatively thick plate as compared the individual force specimen holder  30  in the prior embodiment. Holder  130  includes axially extending apertures  132  for receiving locking screws  134  to secure a specimen in fixed relationship within each of the apertures  138 , with the lower surface  17  of the specimens  16  positioned approximately ⅛ inch below the surface  131  of specimen holder  130 . Thus, the specimens are in locked positions with respect to holder  130 , which is attached to the specimen driver  44  by a shaft  136  held within a central recess  137  of holder  130  by a circular retainer plate  140 . Fastening screws  143  are threaded into apertures  133  within the recess  137  of holder  130 . Retainer plate  140  has a central aperture  141  which slides over shaft  136  and is sealably coupled thereto with an O-ring  144 . The bottom of shaft  136  conventionally includes a conical recess for retaining a ball bearing  150  which engages the upper surface of conical floor  139  of holder  130  to allow the holder  130  to tilt during the grinding process to follow the contour of the different platen configurations. When the central force specimen holder  130  is employed with the new platen configuration described below in  FIGS. 6-14 , it achieves dramatically improved flatness for the specimens  16  fixed in apertures  138  by locking screws  134  due to the geometry of the platens  24  provided as described below. The retainer plate  140  also includes three apertures  145  which receive pins of the specimen driver, as in the previous embodiment, and also may extend into corresponding apertures  135  in the specimen holder. 
     As the specimen driver  44  rotates, specimens  16  are moved from the center of the platen  24  near its axis of rotation toward the outer peripheral edge thereof. In the grinding steps, the specimen is abraded and, together with broken or dislodged abrasive particles from the grinding surface  23 , forms a granular material known as swarf. In an effort to reduce the adverse effect of swarf on the overall grinding step, the grinder  50  typically includes a water dispensing nozzle  52  for directing water onto the surface  23  of the pad  22  attached to the platen  24  to assist in the grinding step and, to some extent, to remove the swarf. 
     Before describing further details of the structure of the invention, an overview of the operation of the grinder machine  50  is provided in reference to  FIG. 2 . The sequence of operation includes lowering the head assembly  40  to position the specimen holder  30  in spaced relationship above the abrasive pad  22  a distance such that the specimens  16  can extend through the apertures  38  in the specimen holder  30  and be captively held at approximately ⅛ inch from their bottom to the platen  24  by the specimen holder  30 . At this point in time, fingers  60 - 65  are retracted within the specimen driver  44  to allow the operator to load the specimens  16  into the awaiting empty apertures  38  of specimen holder  30 . 
     Next, water or other fluid from nozzle  52  is activated, and fingers  60 - 65  are lowered to individually engage the upper surfaces  19  ( FIGS. 15-19 ) of the specimens  16 . At this time, the rotation of platen  24  is initiated, as is rotation of the driver  44 , such that the specimens  16  are swept over the abrasive surface  23  of pads  22  and periodically move above the outer reduced thickness edge  26  of platen  24 . The grinding step lasts for one to five minutes and, more typically, from one to two minutes, after which it is stopped and the pad  22  replaced with a finer grit pad. Two to three pad changes are typically required to achieve the desired flatness of the specimen surface  17 . Between pad replacements, the fingers  60 - 65  are retracted. Head assembly  40 , including the specimen driver  44 , is raised to allow the finished specimens  16  to be removed for subsequent analysis either by a micro hardness tester, microscopy, or other analytical instruments. 
     The grinder  50  of the present invention includes two structural components which individually and/or collectively allow the surface  17  of a specimen  16  to be ground flat to 0.0004 inch over the entire surface of the specimen. Prior art grinders typically achieve flatness of only 0.002 inch to 0.004 inch. This unexpected and remarkable at least ten fold improved result is due to the platen geometry and/or the use of flexible fingers  60 - 65 , allowing specimens  16  to move laterally to some extent in specimen holder  30  eliminating tipping forces on the specimens during grinding. Otherwise, the tipping forces would cause the surface  17  to be ground to a conical shape. The platen design promotes the removal of swarf from the grinding surface due to the surface-oriented height reduction of the platen near the outer periphery of platen  24 . The platen design, which at least partially promotes this result, is due to the surface-oriented height reduction of the platen near the outer periphery of platen  24 . 
     As seen in  FIGS. 6-8 , showing the first embodiment of the platen design, a first platen  24  is shown and has a diameter of typically 8 to 12 inches. The platen has a center area  24   a  in each of these designs. The outer peripheral edge  26  has a surface-oriented height reduction as compared to the center area in the embodiment shown in  FIGS. 6-8  of about 0.01 inch to about 0.1 inch and preferably 0.04 inch provided by linear chamfer  29  of from about 1.5° to about 6° and preferably 3°, as illustrated in  FIG. 8 . The chamfer in the area  26  has a width of from about 0.5 inch to about 1 inch and preferably 0.75 inch. Thus, as the specimen  16  is moved by the rotating specimen holder  30  near the edge of disk  22  supported by the chamfered peripheral edge  26  of platen  24 , any swarf buildup is exposed to the surface-oriented height reduction area  26  and the debris moves off the platen  24  from the abrasive interface grinding surface  23  between the surface  17  of specimen  16  and pad  22  by a combination of the centrifugal force of the platen  24  and the water from nozzle  52 . A gap of about 0.04 inch is provided by the chamfer  29 . This again allows the swarf to escape the interface between surface  17  of a specimen being ground and surface  23  of the abrasive pad  22 . Otherwise, the swarf could unevenly erode the surface  17  of the specimen  16 , leading to an undesirable uneven surface  17 . 
     Instead of the linear chamfer as shown in the embodiment of  FIGS. 6-8 , a platen  24 ′ may include a surface-oriented height reduction area  26 ′, as shown in  FIGS. 9 and 10 , which is the same as area  26  of  FIGS. 6-8  but which is continuously curved at a radius arc of approximately 5 inches, as indicated at  27  in  FIG. 10 . Thus, the surface-oriented height reduction area  26 ′ of about 0.04 inch of platen  24 ′ is provided by a downwardly and outwardly curved radius at the outer edge  26 ′ of platen  24 ′. This allows the swarf to escape the interface between surface  17  of a specimen being ground and surface  23  of the abrasive pad  22 . 
     In another alternative embodiment of the present invention shown in  FIGS. 11 and 12 , a platen  24 ″ is provided and has a surface-oriented height reduction area  26 ″ of about 0.04 inch at its outer edge provide by a compound curve  28  including a first section  28   a , which is concave as viewed in  FIG. 12 , and a second recurved section  28   b , which is convex to provide a wave shape to provide the surface-oriented height reduction area  26 ″ of platen  24 ″. Sections  28   a  and  28   b  are curved at a radius of about 2 inches. The surface-oriented height reduction area  26 ″ of about 0.04 inch of platen  24 ″ is provided by the downwardly and outwardly recurved sections  28   a  and  28   b  at the outer edge  26 ″ of platen  24 ″. The relatively thin pad  22  used in each embodiment allows the pad to conform to the platens, including the recurved outer edge  26 ″ of the platen  24 ″. This allows the swarf to escape the interface between surface  17  of a specimen being ground and surface  23  of the abrasive pad  22 . 
     In yet another alternative shown in  FIGS. 13 and 14 , the reduction in thickness of about 0.04 inch to the outer periphery  26 ′″ of the platen  24 ′″ employed in the grinder  50  of the present invention is achieved by another structure. The platen  24 ′″ includes a surface-oriented height reduction area  33  at the outer peripheral area  26 ′″ having a depth of about 0.04 inch. The relatively thin abrasive pad  22  ( FIG. 7 ), which is adhered to the center area  25 ′″ of platen  24 ′″, drapes down over area  33  to provide a smooth surface-oriented height reduction outer edge presented to a specimen being treated. Thus, this provides surface-oriented height reduction of the platen and a release area for the swarf to be discharged from the abrasive pad  22  of grinding machine  50  during its operation. 
     Having described the base assembly  20  together with the various platen configurations which can be used with either type of specimen holder  30  ( FIG. 3-5 ) or  130  ( FIG. 3A ), a description of the flexible finger structures contained within the specimen driver  44  to achieve their lateral movement allowing the specimens  16  to move within the oversized apertures  38  in specimen holder  30  without encountering tipping forces is now described. There are several manners in which the fingers  60 - 65  are configured to remove any tipping forces on the specimens  16 . The first embodiment of such flexible fingers is shown in  FIGS. 15A-15C . 
     In  FIGS. 15A-15C , a fragmentary perspective view of one of the six cylindrical fingers of specimen driver  44  is shown. The specimen driver  44  includes six equally spaced cylinders  42  at an arcuate distance of about 60° and which are aligned with apertures  38  in the specimen holder  30 . This positions the cylindrical fingers  60 - 65  in alignment with the specimens  16 , as shown in  FIG. 2 . One of the cylinders  42  is shown in  FIGS. 15A-15C  and includes head  41  defining a chamber  54  which receives a source of compressed air through conduits  43  to actuate a piston  45  with suitable sealing rings  46 . Finger  64  (shown in these figures) is secured to the lower end of piston  45 . A return compression spring  46 ′ surrounds the lower end of piston  45  and finger  64  abuts against the top surface of inwardly projecting guide  47  near the lower end of cylinder  42  in spaced relationship to the piston  45 . In each of the following embodiments, pressure is selectively applied to chambers  54  by a suitable conventional electro-pneumatic control to lower fingers  60 - 65  during the grinding operation. When the pressure is released, the return springs  46 ′ retract the fingers into the specimen driver  44 . The diameter of finger  64  and the remaining fingers  60 - 63  and  65  are reduced, such that there is a gap of about 0.0625 inches between the outer diameter of the fingers  60 - 65  and the inner diameter of inwardly projecting guide  47  to allow lateral movement of the fingers and specimens  16  to which they are coupled. Fingers  60 - 65  are each cylindrical rods which extend from the pistons for selectively moving the fingers between a retracted position within specimen driver  44  to extended positions downwardly into engagement with the specimens  16 . Typically, the fingers are stainless steel cylindrical rods. 
     In  FIGS. 15A-15C , each of the fingers  60 - 65  ( 64  shown) terminate in a pad  48  which engages the upper surface  19  of the specimen  16 . Pad  48  has a cup-shaped upper end  56  ( FIG. 15D ) for receiving the end of finger  64 . This junction is surrounded by a flexible rubber jacket  49  which is fixedly coupled to a collar  51 , in turn, mounted to and surrounding a reduced diameter end  53  of finger  64 . The gap between the lower end of finger  64  and inwardly projecting guide  47  allows the pad and specimen  16  to move laterally. Pressure applied to the chamber  54  above pistons  45  in each of the six mounting cylinders provides a force of about 1 to about 12 pounds and preferably about 4 pounds of the pad  48  against surface  19  and, therefore, the face of surface  17  ( FIG. 1 , right end) of the specimen  16  against the abrasive surface  23  of the disk  22  on platen  24  during the grinding operation. The gap between inwardly projecting guide  47  and the cylindrical rods  60 - 65  allow the rods to wobble laterally, as shown by arrows E, as the platen  24  and holder  30  rotate the specimens  16  against the abrasive pad  22 , thus, minimizing any tipping forces which otherwise exist with fixed fingers. This flexibility assists in providing the very flat specimen results. The oversized apertures  38  in holder  30  allow the specimens  16  to also move laterally in each of the embodiments of  FIGS. 15-19  during the rotation of the specimen holder  30 . 
       FIGS. 16A-16C  show an alternative embodiment of each of the finger-holding cylinders of specimen driver  44  in which the inwardly projecting guide  47  and cylindrical rods  60 - 65  diameters are substantially the same but allow the rods  60 - 65  to slide up and down through inwardly projecting guides  47 . A gap of about 0.002 inches between guide  47  and fingers  60 - 65  in each of the embodiments of  FIGS. 16-18  allow the vertical movement. The fingers, thus, move vertically, as indicated by arrow D in these figures. The minimization of tipping forces on the specimen  16  is achieved in this embodiment by a low friction pad  55 , such as Teflon®, positioned between the lower surface of pad  48  coupled to the end of finger  64 , as shown in  FIGS. 16A-16C . This allows the specimen  16  to move laterally in oversized apertures  38 , as also illustrated by arrows E in  FIGS. 16A-16C  from side-to-side as the specimen holder  30  rotates driven by head  44  under the friction force of abrasive surface  23  of pad  22  rotated by platen  24 . This achieves the minimization of tipping forces without modification of the finger mounting cylinders in specimen driver  44 . 
     In another embodiment shown in  FIGS. 17A-17D , the same cylinder and structure as shown in  FIGS. 16A-16C  are employed but the end of fingers  65  (and similar fingers  60 - 64  in this embodiment) are coupled to the upper surface  19  of the specimen  16  by a spring  58  providing a true maximum load of about 15 pounds and having a length sufficient to allow the spring to flex from side-to-side, as shown in  FIGS. 17A-17C , while providing a downward force on the specimen  16  against the abrasive surface  22  and allowing the specimen to move from side-to-side in the oversized apertures  38  in holder  30 . Spring  58  itself is shown in  FIG. 17D  in which the compression spring  58  is shown captively held by and surrounds a reduced diameter end  53  of the finger  65 . 
     In yet another embodiment of the invention shown in  FIGS. 18A-18C , the flexible interface between a finger  65  and the specimen  16  is achieved by an inflatable bellows  70 , which is inflated or may be permanently inflated when pressure is applied to chamber  54  through passageway  72  extending axially through the finger  65  and communicating with a passageway  74  in piston  45 . This lowers finger  65  and may simultaneously inflate bellows  70 , which has a rippled side wall  71  to allow contact with the specimens and promote lateral movement of specimens  16  within holder  30  to, as in the other embodiments, thereby enhancing the grinding effect. 
     Instead of the retractable fingers  61 - 65 , in the embodiment shown in  FIGS. 19A-19C , the fingers are replaced with an inflatable bladder  80  which is sealably coupled to the lower end  81  of an axially extending passageway  82  formed in a specimen driver  44 , which otherwise is of the same configuration as prior specimen drivers but without the use of the piston-driven fingers  61 - 65 . The source of pressurized air through conduit  43  and passageway  82  allows for the selective pressurization of bladder  80 , as shown in  FIGS. 19A-19C , which provides both a downward force against the specimen  16  and allows the flexing of the inflated bladder  80  to permit the specimen to move laterally and hold a specimen against the grinding surface  92  while minimizing any tipping forces that otherwise may be present. Thus, in the embodiment shown in  FIGS. 19A-19C , the retractable fingers are eliminated but the specimen driver  44  is raised and lowered as in prior embodiments with the bladder  80  providing the necessary movement and downward force and permitting lateral movement of the specimen during grinding. The driver head  44  includes apertures and bladders aligned with each of the specimens held by specimen holder  30  so that the multiple specimens  16  are simultaneously subjected to the downward force and lateral movement. 
     In each of these embodiments, the fingers  60 - 65  themselves move laterally or their contact with the specimen allows the specimens  16  to move laterally within the apertures  38  of the specimen holder  30  to minimize the tipping forces on the specimens. In  FIGS. 19A-19C , the fingers can be eliminated and replaced with inflatable bladders directly coupled to the specimen driver. 
     Any one of the embodiments shown in  FIGS. 15-19  can be employed with any one of the embodiments of the platens shown in  FIGS. 6-14 . Likewise, the various platens  24  can be employed with a conventional central force sample holder shown in  FIG. 3A  to achieve a higher degree of flatness of the ground specimens. The combination of the two elements, i.e., a platen with an outer peripheral rim with surface-oriented reduced height and the lateral movement of the specimens achieves the high degree of flatness obtainable by the grinder  50  of the present invention. 
     It will become apparent to those skilled in the art that various modifications to the preferred embodiments of the invention as described herein can be made without departing from the spirit or scope of the invention as defined by the appended claims.