Patent Publication Number: US-2010120341-A1

Title: Portable grinder

Description:
The present invention pertains to a portable grinder with a grinding head, the grinding contact zone of which can be placed against a workpiece. 
     Portable grinders of this type which can be placed against a workpiece so that the machine resists tipping in at least one direction are known from WO 2005/095052 A1. What is described here is, among other things, a grinder with a conical grinding head for grinding down edges. The machine has a ring-shaped plate concentrically surrounding the grinding head by which the grinder can be set against a workpiece surface adjacent to the edge. This portable grinder makes it possible to remove large amounts of the material quickly. The degrees of freedom for the movement of the grinding head, however, are limited. Angle grinders with grinding heads which can be moved into any desired position are also known. 
     The invention is based on the goal of creating a novel portable grinder which combines greater flexibility with respect to the movement of the grinding head with high removal capacity and grinding quality. 
     The inventive portable grinder which achieves these goals is characterized by a stop, which is located a certain distance away from the grinding contact zone. When the grinder is placed against the workpiece, the stop forms a pivot axis for the grinding head and the fulcrum of a lever around which at least one handle can be rotated 
     It is advantageous that the angular position of the grinding head relative to the direction toward the pivot axis is largely determined by the stop, which is located a certain distance away from the grinding contact zone. Changes to this angular position are possible only in association with the approach of the grinding head to the surface of the workpiece in the direction more-or-less perpendicular to that surface. The user of the grinder can therefore, without the tilting of the grinding head in the direction just mentioned, i.e., with a high degree of grinding accuracy, exert a large amount of grinding contact force and a large amount of force in the forward-feed direction parallel to the workpiece surface. 
     In the preferred embodiment, two handles, arranged a certain distance apart, are provided, so that the machine can be held and guided with both hands, wherein, in a projection onto the workpiece, the grinding head and/or the stop is located between the handles. 
     The stop is preferably designed so that the machine can be pressed against the workpiece without the danger of tilting in the direction of the pivot axis. Thus, the user can focus to an even greater degree on the exertion of suitable grinding contact and forward-feed forces. 
     The stop is preferably rounded in a cross-sectional plane perpendicular to the pivot axis. It can be formed, for example, by a pin with a circular cross section. 
     In an especially preferred embodiment of the invention, the stop comprises a roller, which can be set on the workpiece, wherein several rollers arranged a certain distance apart can be provided. The distance between the rollers is preferably adjustable. 
     The rollers can be locked in place on a shaft or can rotate on an axle. Preferably the rollers can be locked in place on the shaft at the desired distance from each other. 
     In another embodiment of the invention, two rollers are provided, and the sides of these roller which face each other comprise slanted rolling surfaces, by which the guide stop makes contact with two different workpiece surfaces, which come together at an angle. A guide stop of this type with rolling surfaces beveled at a 45° angle can, for example, be set against two surfaces of a workpiece which come together at a right angle in order to grind a 45° bevel on the edge formed by the meeting surfaces. 
     The rolling surfaces can be beveled to different angles. For example, one can have a 30° angle, the other a 60° angle, so that a 30° bevel is produced. 
     Whereas a belt grinder head, for example, can be used as the grinding head, a rotating grinding head is used in the preferred embodiment of the invention, wherein the pivot axis formed by the guide stop extends in a tangential direction relative to the rotational axis of the grinding head. 
     The pivot axis formed by the guide stop is also preferably parallel to the surface ground by the grinding head. 
     The guide stop can preferably be pivoted toward the rotational axis of the grinding head and locked in place in a desired position. The position can be adjusted in correspondence with the inclination of the slanted ring-shaped grinding surfaces attached to the end surface of the grinding disk. 
     In the preferred embodiment of the invention, the machine has an elongated housing, which encloses a drive motor for the grinding head, wherein a drive shaft for the grinding head projects, preferably at an angle, from the housing. 
     A handle can be provided a certain distance away from the pivot axis, especially at each of the two longitudinal ends of the housing, as a result of which the length of the lever extending to the pivot axis becomes quite long. This makes it possible in turn to exert a large amount of pressure on the workpiece and thus also to exert high grinding forces. It is advisable here for the lengthwise dimension of the handle near the grinding head to be parallel to the pivot axis. 
     In an especially preferred embodiment, the guide device is a component of a unit which comprises the grinding head and which can be connected to the housing. Thus, for example, the housing of a standard commercial angle grinder can be used, and the angle grinder can be converted into the inventive device. 
     In one embodiment of the invention, the grinding head comprises a multi-layer grinding disk, especially with a wire backing plate, so that high contact forces can be absorbed. It is advisable to provide a hexagonal socket, for example, to prevent normal grinding heads from being used in such grinders. 
    
    
     
       The invention is explained in greater detail below on the basis of exemplary embodiments and the attached drawings, which illustrate these embodiments: 
         FIG. 1  shows a perspective view of a first exemplary embodiment of an inventive portable grinder, 
         FIG. 2  shows the portable grinder of  FIG. 1  in a perspective view rotated 90° from that of  FIG. 1 , 
         FIG. 3  shows a detail of the portable grinder of  FIG. 1 , 
         FIG. 4  shows an exploded perspective view of the portable grinder of  FIG. 1 , which comprises a unit which can be connected to a standard commercial angle grinder, 
         FIG. 5  shows a cross-sectional side view of the unit of  FIG. 4  in isolation, 
         FIG. 6  shows a partial perspective view of the unit of  FIG. 4 , and 
         FIGS. 7-9  show various perspective views of another exemplary embodiment of an inventive portable grinder. 
     
    
    
     A portable grinder comprises an elongated housing  1  with a handle  2  at one end and another handle  3 , designed as a U-shaped bracket, at the opposite end. 
     A drive shaft  4  ( FIG. 4 ) projects from the side of the housing  1 . This shaft is in drive connection with a motor/gear assembly (not shown) installed in the housing  1 . 
     The drive shaft  4  drives a grinding head  5  with a grinding disk  6 . The grinding disk  6  comprises, on the side facing the workpiece  7 , a ring-shaped surface  8  ( FIG. 3 ), which is at a certain angle to the grinding plane and which is in grinding contact with the workpiece  7 . 
     The grinding head  5  is a component of an assembly  9 , shown separately in  FIG. 4 , which comprises a cylindrical connecting piece  10 , which can be clamped to a shoulder  11  on the housing  1 . When this clamping connection is established, the drive shaft  4  is brought into drive connection with the grinding head  5 . 
     The cylindrical connecting piece  10  of the assembly  9  is attached to a U-shaped retaining part  12  with side pieces  13  and  14 , which thus form the sides of the U. A U-shaped sheet metal part  15  is hinged to these side pieces by screwed connections. A certain distance away from each of these screwed connections, another screwed connection is provided, wherein the screw of each these connections passes through a slot  16  in the associated side piece of the U-shaped sheet-metal part  15 . A spark shield  22  is screwed to one side of the U-shaped sheet-metal part  15 . 
     Between the side pieces of the sheet-metal part  15 , the base side of which preferably comprises a Plexiglas-covered opening  17 , there extends a shaft  18 , which is rotatably supported in shaft bearings  21  on the side pieces and on which two rollers  19 ,  20  are seated, which can be connected nonrotatably to the shaft by clamping screws. Instead of the shaft, it would also be possible to provide an axle pin, connected rigidly to the U-shaped sheet-metal part  15 , on which the rollers are free to rotate independently of each other. 
     As can be seen in  FIGS. 5 and 6 , a rotating part  26  of the grinding head  5 , which can be connected to the grinding disk  6 , is supported rotatably by a ball bearing  27  in a bushing part  28 . The bushing part  28  is connected to the connecting piece  10 . The drive shaft  4  engages in a bore  29  in the rotating part  26 , wherein a clutch  30  establishes the drive connection with the rotating part  26 . 
     So that the flat surface of the workpiece  7  can be ground, e.g., so that the projecting part of a weld  23  can be ground off ( FIG. 2 ), the grinding contact zone  26  of the grinder is pressed with the help of the two handles  2  and  3  against the workpiece  7  and with the help of the rollers  19 ,  20 , wherein, in particular, by suitably distributing the load, the user can generate the desired grinding pressure perpendicular to the workpiece surface and also the desired forward-feed in the longitudinal direction of the weld  23 . The rotational axis of the shaft  18  forms a fulcrum for the rotation of the handles and a pivot axis  27  for the grinding head  5 . The distance of the axis from the handle  2  is approximately 300 mm, the distance to the handle  3  about 150 mm. During the process of feeding the grinder forward along the weld  23 , the rollers or wheels  19  and  20  roll over the workpieces surface. Because of the distance between the rollers, which is adjustable, the grinder is unable to tilt in the direction of the rotational axis of the shaft  18 , that is, perpendicular to the forward-feed direction. The grinder sits on the surface of the workpiece  7  with  3 -point support. The guidance by the shaft  18  with the rollers  19  and  20  makes it possible for the user of the grinder to focus fully on the exertion of the correct pressing and forward-feed forces. The rollers  19  and  20  mounted nonrotatably on the shaft  18 , furthermore, make it much easier to guide the grinder straight along the weld  23 . 
     Instead of the rollers, between which the weld is located, it would also be possible to use a shaft with a suitable profile. In the case of the exemplary embodiment according to  FIGS. 5-7 , the same or equivalent parts are designated by the same reference numbers as those used for the preceding exemplary embodiment, where the letter “a” is attached to the reference number in question. 
     The exemplary embodiment according to  FIGS. 5-7  differs from the preceding exemplary embodiment in that rollers  19   a  and  20   a , seated nonrotatably on a shaft  18   a , comprise ring-shaped surfaces  24 ,  25 , oriented at an angle of 45° to the axis of the shaft, on their facing sides. 
     The portable grinder according to  FIGS. 5-7  can therefore be set against the surfaces of a workpiece  7   a  which come together at a right angle and thus be used as a bevel grinder. The machine cannot tip in the direction perpendicular to the longitudinal direction of the bevel. The grinding of flat bevels is thus facilitated even more. 
     The assembly  9  or  9   a  of the previously described bevel grinder can be locked in place in the desired position relative to the rotational axis of the grinding head  5 , wherein this position depends on the angle of inclination of the ring-shaped surface  8  on the grinding disk  7 . The setting is accomplished in such a way that the surface line of the ring-shaped surface  8  is parallel to the workpiece surface in the forward-feed direction. 
     In certain applications, it can be advantageous for only an axle or shaft to rest directly on an edge. The shaft can be profiled, so that it cannot slide off laterally. In such applications the rollers can be pushed all the way to the ends of the shaft and locked in place there.