Abstract:
A blade-mounting adaptor for a power tool has a blade-mounting stud on which the blade is mounted at a first end. The blade is mounted upon the stud in a manner such that it is capable of axial motion along the length of the stud when exertion is applied to the blade. The blade is provided with an adjustable pre-set bias force against the axial motion.

Description:
This invention relates to a spring force adapter for coupling a round cutting tool or the like, such as a grinder blade, to a power tool such as an electric grinder. 
   BACKGROUND OF THE INVENTION 
   Blades used in tools such as electric grinders are utilized in a variety of applications where precise control of the tool may be required. Such applications include shaving mortar or concrete adhering to old bricks, tiles, concrete or frames and have the objective of removing such foreign matter from the substrate evenly and completely without damaging the substrate. As the grinder blade is engaged with the surface significant loading of the tool can result. The application of excessive force by the tool operator can result in overloading the tool, resulting in excessive current draw, overheating, excessive wear to tool components, or failure. 
   Such grinders generate significant amounts of dust and debris during operation. As a result of increasingly strict health and environmental regulations and concerns, the grinders often are provided with a safety cover or shield to contain or restrain the dust and debris, along with a vacuum device to collect the materials. Often the safety cover or shield has a mechanism, such as brushes, to provide a measure of a seal between the cover and the workpiece. The blade must be positioned appropriately with respect to the seal to allow appropriate contact with the workpiece to be made while brush contact is preserved. 
   The blades utilized in connection with the grinders and similar tools are interchangeable and replaceable. It is thus important that each blade when mounted on the tool is positioned properly with respect to the cover or shield to permit proper blade-workpiece contact to be maintained as blades are exchanged and replaced. As grinding is a force-intensive action, sufficient force must be applied to the tool to maintain appropriate contact between the rotating grinding wheel and the workpiece, but not excessive force that can stress or overload either the tool motor or grinding wheel. 
   It is accordingly the objective of the present invention to provide a coupling for the mounting of a grinder blade or similar rotating tool that can minimize or eliminate damage to the electrical tool due to repetitive and rapid changes in the load or heavy loads and which accommodates the necessary blade positioning for proper and efficient tool operation. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In accordance with the foregoing and other objectives the present invention is a coupling upon which a grinder blade or other rotating tool element is mounted and which in turn is mounted to the tool drive shaft. The blade is spring biased into an operating position at the end of the coupler shaft. Thus the position of the blade with respect to the tool remains constant when blades are changed. Excessive axial forces applied to the blade, such as by the operator pushing the blade into a workpiece, overcome the spring force applied to the blade, allowing the blade to retract along the coupler, relieving the force on the blade. As the excessive force is removed the blade returns to the original position. The level of spring bias is adjustable. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     A fuller understanding of the invention will be achieved upon consideration of the following detailed description of a preferred but nonetheless illustrative embodiment thereof, when considered in conjunction with the annexed drawings, wherein: 
       FIG. 1  is an exploded perspective assembly diagram showing an embodiment of the present invention and a blade as installed thereon; 
       FIG. 2  is a perspective view of the invention with an installed blade; 
       FIG. 3  is an elevational cross-section view thereof taken along line  3 — 3  of  FIG. 2 ; 
       FIG. 4  is a corresponding elevational cross-section view showing the blade in a retracted position as when excessive force is applied to the tool; 
       FIG. 5  is an exploded assembly diagram showing an alternative embodiment of the invention; and 
       FIG. 6  is an elevational cross-section view thereof taken along line  6 — 6  of  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With initial reference to  FIGS. 1–3 , a power tool, such as an electric hand-held grinder (not depicted) has a rotating shaft or arbor member to which a blade, such as grinder cup blade  20 , is mounted. The present invention provides a coupling between the blade and arbor shaft, and includes adaptor puck  10  that mounts upon the arbor shaft, typically through threaded bore  10  which allows the puck to be installed upon a correspondingly threaded portion of the power tool shaft. The puck  10  has a projecting threaded axle portion  14  extending from the puck body. The threads of the axle are preferably of the same pitch and diameter as the threads of the tool&#39;s shaft member. Blade-mounting stud  18 , which is of polygonal and preferably square cross-section, has a threaded bore extending therethrough with threads complementary to the threads of the axle  14 , such that the mounting stud can be affixed upon the axle, and thus serves as an extension of the arbor shaft. The face vertices or corners of the stud are threaded along their length  16  to allow the mounting of complementary elements on the stud. It is to be recognized that the puck  10  and blade mounting stud  18  may be formed as a unitary member. Alternatively, the stud may have a bore portion allowing the stud to be mountable directly upon the arbor shaft without an intermediate puck element. 
   Coiled compression spring  22  is mounted on the blade-mounting stud  18  between opposed inner and outer bowl washers  24  and  26 , each of which has a central aperture to allow it to be mounted upon the stud. The aperture wall of the inner bowl washer  24  is circular, sized and threaded to mate with the stud threading, allowing the position of the washer along the length of the stud to be adjusted. The aperture of the outer bowl washer  26  is square, sized to allow the washer to slide freely upon the stud but without being able to rotate with respect to the stud. 
   The blade-mounting stud  18  is dimensioned to be received by the central circular mounting bore of bowl blade  20 , which is of conventional construction. Blade retaining bolt  28  threads into the bore of the distal end of the mounting stud, its head  30  holding the blade upon the mounting stud. 
     FIGS. 2 and 3  depicts the coupler with the blade  20  mounted on the stud  18  in a normal operating position. The blade is located at the distal end of the stud, retained by the head  30  of retaining bolt  28  threaded into the stud, and is positioned between the bolt head  30  and the outer bowl washer  26 . The outer bowl washer is urged against the blade by spring  22 , the degree of force applied by the spring being controlled by the position of the inner bowl washer  24  along mounting stud  18 . The uncompressed length of spring  22  may be such that, with the inner bowl washer  24  positioned adjacent the puck  10 , the outer bowl washer  26  is not urged by the spring into a position along the mounting stud where it would conflict with the mounting of the blade on the stud. Once the blade is mounted upon the shaft the spring force applied to the blade through the outer bowl washer can be adjusted as appropriate by threading the inner bowl washer  24  along the stud as appropriate. Sufficient friction between the blade and outer bowl washer  26  and retaining bolt is present to drive the blade during use. The axial force applied by the spring to the outer bowl washer is chosen to allow the spring to further compress, absorbing excessive axial force applied to the blade by the user, and allowing the blade to move inwardly along the stud. 
     FIG. 4  depicts the coupler when excessive operator axial force has been applied. Spring  22  is further compressed by the reaction force of the workpiece, the blade thus retracting upward along the stud  18  until the additional spring force resulting from the further compression matches the operator force. As the operator force varies, the degree of compression of the spring automatically compensates therefor, the blade moving back and forth along the stud. When the operator force returns to the proper level the blade returns to its normal position at the end of the stud, resting against the head of the retaining bolt  28 . Because of the square cross-section of the shaft and the mating shape of the outer washer  26 , the washer does not rotate, and thus remains in positive, fixed drive contact with the blade. 
   Oftentimes the body of a cup blade  20  is of an unhardened metal construction, and is relatively thin. Particularly when mounted to a square spindle slippage may occur, with resulting wear on the cup wheel body. This can lead to the need for blade replacement before the cutting edge is worn. 
     FIGS. 5 and 6  depict an alternative embodiment of the invention capable of resolving this problem. In this embodiment blade  32  is of a modified design, with an enlarged central planar section  34  surrounding the central mounting bore  36 , which remains of standard size. Adaptor  38  mounts to the central section of the blade by screws  40 , through adaptor mounting bores that thread into corresponding bores  44  in the central portion of the blade. The adaptor may be provided with studs  46  which engage other of the blade bores  44 , and which assist in aligning the adaptor with the blade for mounting and also rigidify the adapter-blade connection. The adaptor eliminates the blade body-retaining bolt contact, and strengthens the blade body. 
   Blade-mounting stud  46  is multi-sided, and is shown with a main hexagonal portion having the thread surfaces  16  at the face vertices. An extension portion  48  is of reduced diameter, and may be of generally square cross-section, sized to accommodate the blade-mounting bore  36  and to be accommodated by the central mounting bore  50  of adaptor  38 , which is of complementary shape and dimensions. Mounting stud  48  again has internal threading to allow it to be mounted either directly to a power tool arbor (not shown) or to an adaptor puck (also not shown). Inner and outer bowl washers  52 ,  54  function in the same manner as in the previous embodiment, inner washer being threaded to allow positioning along the stud  46 . Outer washer  54 , however, may have a circular mounting bore, as a non-slip connection between the blade  32  and the stud  46  is established through the mating of the sides if stud extension  48  and adaptor mounting bore  50 . Blade retaining bolt  28  again retains the blade (and affixed adaptor  38 ) at the end of the stud  48 . As in the prior embodiment adjustment of the inner bowl washer  52  varies the spring force applied to the blade, allowing the blade to retract along the stud when excessive axial force is applied to the blade by the user.