Workpiece clamp and tool shielding device and combination thereof with a tool applying apparatus
United States Patent 1 Narang [4 1 Apr. 15, 1975 WORKPIECE CLAMP AND TOOL SHIELDING DEVICE AND COMBINATION THEREOF WITH A TOOL APPLYING APPARATUS [76] Inventor: Rajendra K. Narang, 9265 Lincoln Dr., Apt. E-l, Northfield, Ohio [22] Filed: Dec. 13, 1973 [21] App]. No.: 424,209  
 Primary Examiner-James J. Gill Assistant Examiner-Anthony V. Ciarlante Attorney, Agent, or Firm-John Harrow Leonard [57] ABSTRACT A housing is detachably connected to one arm of the C-frame of a hardness tester. The arm carries a reciprocable plunger on one end of which is a penetrator. The other arm carries an adjustable anvil. The penetrator is forced by the plunger against a workpiece disposed on an anvil for testing hardness. The housing wall is in surrounding spaced relation to the plunger. The housing carries a workpiece clamping and tool shielding sleeve which is coaxial with the plunger and penetrator and which projects through the end of the housing adjacent the anvil so that the outer end of the sleeve can engage the workpiece over a substantial area in surrounding spaced relation to the point of application of the penetrator. The sleeve has at its inner end a wide outer radial flange which extends close to the side wall of the housing. An annular abutment plate is secured in the housing in coaxial relation with the flange by a snap ring. A compression coil biasing spring is interposed between the flange and the abutment plate and biases the sleeve to an extended position in which its outer end extends axially beyond the penetrator so that it can effect initial engagement with the workpiece when the sleeve is in its extended position and the plunger concurrently is in its retracted position. In this position the sleeve also surrounds and shields the penetrator. The spring applies sufficient biasing force to clamp the workpiece in fixed position on the anvil preparatory to and during penetration of the workpiece by the penetrator.  
 8 Claims, 3 Drawing Figures PMEHT&#39;ESAFR 1 SEES 3,877. 298  
 SHEET 1 95 2 v WORKPIECE CLAMP AND TOOL SI-IIELDING DEVICE AND COMBINATION THEREOF WITH A TOOL APPLYING APPARATUS BACKGROUND OF INVENTION 1. Field of Invention Detachable combined workpiece clamping tool and tool shielding attachment for tool applying apparatus.  
 2. Prior Art The present invention is directed broadly to a clamping and shielding device for clamping a workpiece fixedly in position preparatory to and during engagement thereof by a pointed tool which is caused to engage the workpiece pointed end foremost under pressure and perform thereon an operation, and for shielding the tool preparatory to its engagement with the workpiece, during its operation, and during its withdrawal. The invention is particularly adapted for hardness testers and for purposes of illustration is described herein specifically in connection therewith.  
  Heretofore hardness testers have been provided in which a combined work clamping and tool shielding sleeve attachment is mounted in coaxial relation with a penetrator carrying plunger so that one end of the sleeve engages the workpiece over an area in surrounding radially spaced relation to the plunger preparatory to applying the penetrator, and so that the sleeve maintains its firm clamping contact with the workpiece and a shielding relation to the penetrator during movement of the plungertoward the workpiece for effecting the penetrating or testing operation.  
  Such a structure broadly is disclosed in US. Pat. No. 2,804,769, of C. W. Clark, Sr issued Sept. 3, 1957. This structure is built, however, as a part of the hardness tester itself as a result of which the hardness tester and the clamping and shielding structure must be disassembled in part for servicing either one. The tester must be recalibrated after the clamping structure is installed, and it is difficult to determine whether possible errors are in the tester or are introduced by the auxiliary structure. This is because the clamping force of the biasing spring is itself inherently varied by the manner of its installation.  
  Further, in this prior structure, the biasing spring applies its force to the inner end of the clamping and shielding sleeve near or slightly inwardly radially from the outer peripheral limit of the side wall of the sleeve. Again, the clamping and shielding sleeve is carried in a coaxial outer sleeve which is adjustable by a threaded connection axially of, and relative to, its support. Thus, when the combined clamping and shielding sleeve is free of the work, the spring pressure transferred by the clamping and shielding sleeve to the outer sleeve causes a succession of minute and cumulative incremental migrations of the outer sleeve to a different rotated position and, therefore, to a different axial position relative to the frame of the tester. This results in the pressure applied by the clamping and shielding sleeve to the workpiece varying slightly, depending upon the degree to which the spring has been initially compressed due to the accumulated movement of the clamping sleeve endwise of the spring in the spring collapsing direction by the outer sleeve.  
 SUMMARY The device of the present invention is such that the initial compression of the biasing spring, in the extended position of the combined clamping and shielding sleeve, is fixed and its force cannot be varied or changed by any relative movement of the parts of the device or in any manner other than by disassembling the device and installing a new spring. The device can be detachably secured in place in proper operating position relative to the C-frame and penetrator of a conventional hardness tester so as to assure that it performs its function properly in relation thereto. Its clamping forces and parts are self-contained so that it can be removed for servicing, testing, or recalibrating of the hardness tester and reinstalled without requiring any adjustment of itself or of the tester in the installed position of the device and without disturbing the calibration. This is due to the forces applied by the device itself to the work being self-included so as to have a fixed effect which remains constant and can be allowed for in calibration of the tester.  
  Various other objects and advantages of the invention will become apparent from the following description wherein reference is made to the drawings.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a conventional hardness tester with the device of the present invention installed thereon;  
  FIG. 2 is an exploded perspective view of the principal functioning elements of the clamping and shielding device of the present invention; and  
  FIG. 3 is an enlarged vertical sectional view of the device and is taken on the line 33 of FIG. 1. parts of the hardness tester being shown diagrammatically in connection therewith for purposes of illustration.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the device is shown in connection with a conventional hardness tester, indicated at 1, comprising a C-frame 2 having an upper arm 3 and lower arm 4. The upper arm 3 has a cylindrical boss 5 depending from its under face and through which extends a quill 6 which carries a plunger 7 having at its lower end a penetrator or diamond tip 8. A conventional reading gauge is carried by the upper arm 3 and connected to the plunger. Power means, not shown, such as selected weights, are provided for driving the plunger 7 downwardly with a preselected force to an extended position into penetrating engagement with a workpiece W to determine the hardness which is then reflected by the gauge.  
  The workpiece W is supported on an anvil 9 which is adjustable by conventional adjustment means 10 to a height such that the penetrator 8 can be brought firmly into engagement therewith when the plunger is in a downwardly extended position.  
  With testers of this type considerable difficulty is encountered in testing workpieces at a location thereon such that the weight of the workpiece is unbalanced relative to the anvil or point of application of the penetrator. The unbalance tends to rock the workpiece and impose inordinate turning moments and stresses impose forces on the tip which result in erratic readings, but also frequently are of such intensity as to fracture the diamond point or break it loose from its mounting. All too frequently an operator will rely on the force applied by the point or tip to the workpiece to hold the workpiece firmly against the anvil. Even when the penetrator has penetrated the piece to the extent caused by the selected power means. the workpiece can rock or shift and snap off the penetrator tip or introduce frictional and lateral stresses and turning moments such that the components of force normal to the workpiece result in inaccurate readings.  
  In accordance with the present invention, a combined workpiece clamping and tool device is provided which can be readily attached to or detached from the arm 3 in a position so as to engage the workpiece and hold it firmly in position against the anvil preparatory to, and during, operative engagement of the workpiece by the penetrator 8. The device is spring biased so as to hold the workpiece firmly by a force equal to or greater than the total force which is to be applied to the workpiece by the penetrator 8, but which force is distributed on an annular area of the face of the workpiece coaxial with and spaced radially outwardly from, and disposed generally so as to constrain the workpiece from rocking or imposing any unforeseeable forces and factors affecting the reading.  
  In the form illustrated, the invention comprises a holding ring 12 which is adapted to bear against the under face of the arm 3 and to be secured in this position on the arm 3 by suitable bolts 13 in coaxial relation with the boss and plunger 7. The ring 12 can be left permanently installed on the arm 3. Preferably, the inner diameter of the ring 12 is such that it fits snugly the outer periphery of the boss 5. The ring 12 is of such length that it extends downwardly below the under face of the boss 5.  
  The clamping and shielding device includes an outer housing 15 which is open at its upper and lower ends and has at its upper end an enlarged portion 16 which preferably is circular in horizontal cross section and fits snugly within the ring 12 in coaxial relation therein and with the plunger 7. The portion 16 has a radially outwardly open annular groove 17 which is engageable by a plurality of manually operable clamping screws 18 for holding the housing 15 in place in coaxial relation with the plunger 7 and with its upper edge against the boss 5. The housing 15, at its lower end, has an opening 19 coaxial with the annular portion 16 and with the plunger 7.  
  Carried by the housing 15 is a workpiece clamping and tool shielding sleeve 20 which has an upper portion within the housing 15 and a lower portion projecting downwardly through the opening 19 below the lower end of the housing 15. The sleeve 20 is supported for axial movement in the housing 15 in coaxial relation with the plunger 7 with slight radial clearance relative thereto and relative to the peripheral wall of the opening 19 so as not to engage the plunger and bind thereagainst or against the housing as the sleeve is moved axially of the plunger 7 and housing 15. At its inner end the sleeve 20 has a wide outwardly extending radial flange 21. The flange extends outwardly beyond the outer peripheral surface wall of the sleeve 20, preferably a distance which is equal to or greater than the outer diameter of of the sleeve 20; for example, so that the outer diameter of the flange is three or four times the diameter of the sleeve 20.  
  Detachably mounted within the housing 15 is a spring abutment plate 23 which is held in place by a suitable snap ring 24 engaged with an internal annular groove 25 in the inner annular wall of the housing 15. The spring abutment plate 23 is annular with a central passage 26 slightly larger in diameter than the plunger 7. The plate 23 has slight radial clearance with respect to the inner peripheral wall of the housing 15 so that it can move in a direction from the ring 24 toward the flange 21.  
  A coil compression spring 27 is interposed between the plate 23 and the flange 21. The spring 27 bears at its upper end against the plate and at its lower end against the flange 21, thus holding the plate firmly against the ring 24 while biasing the sleeve 20 downwardly to a fully extended position in which the flange 21 engages an inner bottom wall portion 30 of the housing 15. The spring is preferably of constant strength and for most testing devices applies a total force of from 15 to kilograms to the flange. The spring strength should be about 10 to 20 percent less than the pressure applied by the penetrator so that the clamping and tool shielding sleeve is held firmly against the work but does not impose on the C-frame arms any pressure in addition to that imposed by the penetrator during the penetrating operation.  
  In the fully extended position of the sleeve 20, its lower end is disposed below the penetrating point of the penetrator 8 a short distance when the penetrator and plunger 7 are in their fully retracted position. Thus a workpiece W can be placed on the anvil 9 and the anvil adjusted upwardly to force the workpiece firmly against the bottom of the sleeve 20 and partially compress the spring 27 to a degree such that the predetermined strength of the spring is applied to the workpiece and holds it in fixed position on the anvil. The lower end of the sleeve 20 preferably engages the workpiece a considerable distance outwardly radially from the point of application of the penetrator 8. For example, in a conventional tester, the internal diameter of the sleeve 20 may be K inch.  
  Here it is to be noted that no adjustment or maladjustment of the spring 27 can result from installing or removing the device as all of the operating forces of the hold-down device are developed within the device and are self-contained. Accordingly, the device can be removed from the tester without in any way disturbing its own inherent biasing forces and without disturbing the setting of the tester or any part thereof. Thus both the device and the tester can be calibrated separately and connected together without danger of introducing some additional force component which could affect the reading. For example, the device can be removed and the tester calibrated. The device then can be installed and the tester further calibrated to allow for the fixed factor introduced by the device itself, such as the reactionary force applied to, and tending to spread apart, the arms of the C-frame. Any force factor introduced by the device is constant. Therefore, at any time in the future, the device can be removed from the tester and the tester then serviced and calibrated and the device reattached with the assurance that the reading will remain accurate as the constant force factor of the device can readily be allowed for because known from its original calibration. The device can be removed readily for rechecking the reading of the tester and for servicing either the tester or the device, or both, and reinstalled without any appreciable loss of time and without the introduction of any new force component.  
  The spring 27 engages the flange 21 outwardly a very great distance from the outer peripheral surface of the sleeve 20. Consequently, any slight changes in pressure applied by the spring at any point around its peripheral area of engagement with the flange 21 cannot cause any appreciable rocking of the sleeve and flange and resultant cocking of the sleeve into any binding relation to the wall of the opening 19 or to the surface of the plunger 7. There is no axial adjustment of any part of the device relative to the other parts or to the tester.  
  The force applied on the shield by the spring 27 is less than that applied by the point of the penetrator 8. The shield 20 engages the workpiece outwardly at a great distance from the point of the penetrator 8. The larger lever arm of the shield. as compared to that of the point of the penetrator 8. resisting rocking of the workpiece. assures that the workpiece cannot impose any turning moments or lateral stresses on the point.  
  The spring 27 does not have to be of constant strength, but it preferably is greater than required for a mere hold-down operation so that it does not become permanently deformed and lose its original strength after repeated used. All of the hold-down forces are self-contained and isolated from the plunger and point. The point is protected in both its retracted and in its extended positions.  
  A window 31 is provided at the lower end of the sleeve 20 so as to permit observation of the exact point of application of the penetrator 8 to the workpiece.  
 Having thus described my invention. I claim:  
  1. A detachable workpiece clamping and shielding device for a hardness tester having a rigid frame. a workpiece supporting anvil carried by the frame. a load applying plunger mounted on the frame in alignment with the work supporting face of the anvil and for axial movement toward the anvil to an extended position and away from the anvil to a retracted position. a penetrator on the end of the plunger facing the anvil. said device comprising;  
 a detachable hollow housing of fixed length and having coaxial openings at its ends. respectively;  
 a work clamping and shielding sleeve in the housing and having a portion at one end extending through and beyond one end of the housing;  
 said sleeve being supported by the housing for movement endwise thereof to an extended position in which said one end of the sleeve is a predetermined distance outwardly endwise beyond said one end of the housing and to a retracted position in which said one end of the sleeve is a lesser distance outwardly from said one end of the housing;  
 said sleeve having an end portion disposed in the housing and having an external peripheral flange on said end portion. which flange is wide relative to the outer periphery of said one end of the sleeve;  
 a fixed abutment in and carried by. the housing between said end portion and said other open end of the housing;  
 a coiled compression spring in the housing coaxial with the sleeve and bearing at one end against the abutment and at the other end against that annular area on that face of the peripheral flange which faces toward the abutment. and which area is near the periphery of the flange and outside of the axially projected outermost periphery of said one end of the sleeve onto the flange and biasing the sleeve to a predetermined maximum extended position;  
 a second fixed abutment in the housing operative to limit the movement of said sleeve axially in the extending direction to said predetermined maximum extended position.  
 said assembled housing. sleeve. abutments and spring constituting a self-contained unit; and  
 connecting means adapted for connection in fixed position on the frame of a hardness tester. said connecting means being detachably connectable to said housing at the end of the housing opposite from said one end for securing the housing in fixed radial and axial position relative to said holder.  
  2. A device according to claim 1 wherein the housing has an interior wall which. at the portion between the flange and abutment. is circular in cross section; and  
 the outer periphery of the flange is near to. but  
 spaced from. the interior peripheral wall of the housing.  
  3. A device according to claim 1 wherein the housing has an internal peripheral groove. the fixed abutment is an annular member coaxial with the sleeve and groove and movable axially thereof. and a snap ring in engagement with the groove and extending inwardly so as to engage the outer margin of that face of the annular member which is opposite from the spring so as to limit the movement of the annular member relative to the housing in a direction away from the sleeve.  
  4. A device according to claim 1 wherein said connecting means comprise an annular holder:  
 means for attaching the holder to the frame of a hardness tester in coaxial relation to the tool and plunger. and in fixed position circumferentially and axially:  
 said housing having its said other end portion shaped for telescopically slip fitting reception relative to said holder: and  
 releasably connecting elements cooperable with the holder and housing and operable to secure the housing in said fixed axial position relative to the holder.  
  5. The structure according to claim 1 further including a hardness tester having a rigid frame. a workpiece supporting anvil carried by the frame. a load applying plunger mounted on the frame in alignment with the work supporting face of the anvil and for axial movement toward the anvil to an extended position and away from the anvil to a retracted position. a penetrator on the end of the plunger facing the anvil; and  
 means detachably connecting said housing to the frame in coaxial. surrounding. and radially spaced. relation to the plunger and with said one end of the sleeve extending beyond the penetrator when the sleeve is in its extended position and concurrently the plunger is in its retracted position.  
  6. A device according to claim 1 wherein the outer diameter of the flange is at least twice the outer diameter of the sleeve at said one end.  
  7. A device according to claim 1 wherein said second abutment is in axially spaced relation to the first mentioned abutment and is disposed between said other end of the housing and the opposite face of said flange, and is aligned axially with an annular portion of said opposite face of the flange near the outer periphery thereof, and is engageable by the flange near said outer periphery to limit said movement of the sleeve by the spring in the extending direction to said predetermined maximum extended position. and to prevent rocking of the sleeve in a direction transversely of its axis in said maximum extended position.  
  8. A device according to claim 1 wherein said portion of the sleeve which extends through said one end of the housing is in radially spaced relation throughout its peripheral extent, to the wall of the housing defining the opening through which said portion extends so as to be free from guiding contact therewith.