Abstract:
A hand tool for holding a spinning disc while the circumference of the disc is being ground is noteworthy for its ability to accommodate disks of various thicknesses. The disc is gripped between two resilient grippers that rotate with the disc. The grippers are mounted for rotation to the jaws of the tool. The jaws slide open and closed on two spaced parallel guide pins that are parallel to the axes of rotation of the grippers. This assures that as the jaws are opened or closed to accommodate discs of different thicknesses, the axes of the grippers remain colinear.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is in the field of hand tools and more specifically relates to a hand tool for holding a disc while the circumference of the disc is being ground to produce a disc having a desired diameter. 
     2. The Prior Art 
     One way of producing a disc of a desired diameter is as follows. A number of disc-shaped blanks are punched from a sheet or plate of the chosen material. These blanks do not have the desired final diameter due to the fact that a punch of the right size may not be commercially available, and due to the lack of precision inherent in the punching process. In addition, the punched blanks may have burrs or irregular edges. The tool of the present invention is used for holding a punched blank while the circumferential edge of the blank is ground, to bring it to the desired diameter and to eliminate the burrs and irregularities. 
     In U.S. Pat. No. 163,683 issued May 25, 1875 to Norton, there is shown a clamp for use in grinding watch crystals. The crystal is held between elastic-faced grippers each of which rotates about an axis that is perpendicular to a jaw of the clamp. The jaws open and close by pivoting about a pin. 
     In U.S. Pat. No. 2,551,648 issued May 8, 1951, to Suben, there is shown a tool for use in beveling a lens. As in Norton&#39;s tool, the jaws are connected by a pivot. Also, a spring is used to urge the jaws closed. Each jaw terminates in a rotating gripper. 
     The tools of Norton and of Suben are designed for working with discs of a particular thickness. Because the jaws are connected by a pivot, as the jaws are opened to accommodate a thicker disc, the axes of the rotating grippers cannot remain in a single straight line. The elastic facing of the grippers can accommodate only relatively small variations of disc thickness. Larger variations in disc thickness disrupt the gripping action and may cause the disc to become dislodged. 
     With this problem in mind, the present inventor set out to design a disc grinder capable of being used with discs having a wide range of thicknesses. 
     SUMMARY OF THE INVENTION 
     The main object of the present invention is to provide a disc grinder that can, without adjustment, be used to grind discs that have a wide range of thicknesses. 
     In accordance with the present invention, the jaws open and close along a pair of parallel guide rods that assure that the axes of rotation of the grippers remain colinear as the jaws are opened and closed. 
     In a preferred embodiment, the jaws are biased to an open position, and the user squeezes the jaws closed by overcoming the biasing force. 
     In a alternative embodiment, a threaded member is rotated to draw the jaws together. 
     In all embodiments, the axes of the rotating grippers remain colinear as the jaws are opened and closed, thereby permitting the tool of the present invention to be used for grinding discs of various thicknesses. 
     The novel features which are believed to be characteristic of the invention, both as to organization and method of operation, together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawings in which a preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and a description only and are not intended as a definition of the limits of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing a disc grinder of a type known in the prior art, in use; 
     FIG. 2 is a diagram showing the prior art disc grinder of FIG. 1 when a thicker disc is being ground; 
     FIG. 3 is a side elevational view showing a disc grinder in a preferred embodiment of the present invention; 
     FIG. 4 is a front end elevational view of the disc grinder of FIG. 3; 
     FIG. 5 is a side elevational view in cross section of the disc grinder of FIG. 3; 
     FIG. 6 is a perspective view of the disc grinder of FIGS. 3,  4  and  5  in use; 
     FIG. 7 is a side elevational view partly in cross section showing a disc grinder of an alternative embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 show a tool of a type known in the prior art, for grinding discs. The tool includes handles  12  and  14  which the user squeezes while the disc is being ground. Jaws  18  and  20  are pivotally connected through the pin  16 . The tool includes resilient grippers  22  and  24 , which are mounted for rotation about the axes  30  and  32  on the axles  26  and  28 , respectively. 
     FIG. 1 shows the tool grasping a disc  34 , and FIG. 2 shows the tool grasping a disc  36  that is thicker than the disc  34 . In order to grasp the thicker disc  36 , the jaws  18  and  20  must open wider, causing the axes  30  and  32  to depart in FIG. 2 from the colinear disposition shown in FIG.  1 . This causes an irregular camping action which could cause the disc  36  to be ejected from the tool. 
     From consideration of FIGS. 1 and 2 it can be correctly seen that because the jaws are pivotally connected by the pin  16 , the tool is limited to use on discs of a particular thickness, in the absence of some correcting mechanism. 
     For the ordinary mechanic who is not engaged in mass production, it does not make sense to purchase an assortment of tools in anticipation of a need to grind discs of various thicknesses. The present inventor recognized the desirability of having one tool capable of grinding discs of various thicknesses. As will be described in greater detail below, this objective was achieved by providing a mechanism for keeping the axes of the grippers in a colinear relationship as the jaws are opened and closed. 
     FIGS. 3,  4  and  5  show a preferred embodiment of the tool of the present invention. 
     In the preferred embodiment of FIGS. 3,  4  and  5 , a disc  54  is positioned by the user between the grippers  42  and  44  in the position shown in the drawings, and then the jaws  38  and  40  are squeezed together by the user until the grippers  42 ,  44  firmly grip the disc. The disc  54  is not part of the invention, and is shown in dashed lines in the figures. The grippers  42  and  44  are affixed to axles  46  and  48  respectively which are mounted for rotation in the jaws  38  and  40  by use of the ball bearings  56  and  58 , as shown in FIG.  5 . The gripper  42  rotates about the axis  50  and the gripper  44  rotates about the axis  52 . 
     The present inventor has succeeding in assuring that the axes  50  and  52  always lie in the same straight line regardless of the thickness of the disc  54 . In accordance with the preferred embodiment of the present invention, this desirable result is accomplished by the use of two guide pins  60  and  62 . In the preferred embodiment, the guide pins  60  and  62  are set into the jaw  40  by inserting the guide pins into tight-fitting bores in the jaw  40 . The bores in the jaw  40  are extensions of the bores  64  and  66  that extend entirely through the jaw  38 , as best seen in FIG.  5 . However, the bores  64  and  66  in the jaw  38  have a slightly larger diameter than the bores in the jaw  40 . This permits the jaw  38  to slide along the pins in a close sliding fit. 
     In one way of manufacturing the tool, the bores for the guide pins as well as the bores for the ball bearings are made in a single solid block of metal to assure alignment. Thereafter, the single block is sawed into two halves which become the jaws  38  and  40 . In another way of making the tool, the jaws  38  and  40  are formed first and then clamped tightly together while the bores are made. Regardless of which technique is used, the axes  50  and  52  must be colinear, and they must be parallel to the guide pin bores in the jaw  40  and the bores  64  and  66  in the jaw  38 . This assures that as the jaws  38  and  40  slide along the guide pins  60  and  62 , the axes  50  and  52  will remain colinear. 
     In the preferred embodiment, the jaws  38  and  40  are biased apart by the compression spring  68  which is held captive on the rod  70 . The rod  70  is provided with a head  72  that prevents the jaw  38  from being removed from the jaw  40 . 
     The embodiment of FIGS. 3,  4  and  5  is used in the manner shown in FIG.  6 . The disc  54  is placed between the grippers  42  and  44  and is manually centered with the axes  50  and  52 . Then, squeezing the jaws  38  and  40  between his thumb and forefinger, the user advances the tool toward the grinding wheel  74  until the disc  54  comes into contact with the grinding wheel  74 . 
     Assuming that at the point of contact between the grinding wheel and the disc, the grinding wheel is moving vertically downward, it is clear that if the axis  50  is vertical, the disc will not spin. It is also seen that if the axis  50  is horizontal, the disc will spin rapidly. It has been found, as expected, that if the axis  50  is inclined slightly from the vertical the disc will spin at an intermediate speed. Thus, the user can control the speed with which the disc spins by slightly inclining the axis  50  with respect to vertical. In normal usage, the grinding wheel is spinning much more rapidly than the disc  54 , but the spinning of the disc is highly desirable because it distributes the grinding action uniformly around the circumference of the disc, thereby preventing flat spots from developing. 
     FIG. 7 shows an alternative embodiment in which a lag screw  76  is used for opening and closing the jaws. The threads of the lag screw  76  engage threads in the jaw  40 , and the smooth portion of the shank of the lag screw passes through a clearance bore in the jaw  38 . The lag screw is provided with a large head  78  that is knurled on its circumference so that it can easily be turned. 
     Thus, there has been described a disc grinding hand tool that is capable of holding discs of various thicknesses during the grinding process. This is made possible by providing two pins that are affixed to one of the jaws in a direction parallel to the spin axis of the disc, and on which the other jaw slides. 
     The foregoing detailed description is illustrative of one embodiment of the invention, and it is to be understood that additional embodiments thereof will be obvious to those skilled in the art. The embodiments described herein together with those additional embodiments are considered to be within the scope of the invention.