Patent Publication Number: US-8113921-B2

Title: Tool set for an eccentric grinder

Description:
CROSS-REFERENCE 
     The invention described and claimed hereinbelow is also described in PCT/EP2007/064154, filed on Dec. 19, 2007 and DE 10 2007 007 787.6, filed on Feb. 16, 2007. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119 (a)-(d). 
     BACKGROUND OF THE INVENTION 
     The present invention is directed to a tool set for an eccentric grinder having at least two grinding discs. 
     A known hand-held sander (U.S. Pat. No. 5,018,314) designed as an eccentric grinder includes a circular grinding disc which is installed via a pivot bearing on an eccentric output shaft of an eccentric gearing driven by an electric motor. The grinding disc includes a support body and a grinding means carrier. The support body of the grinding disc includes a flat plate and a bearing tube which is designed as a single piece with the plate and extends away from the plate at a right angle, and in which the pivot bearing is inserted. The circular grinding means carrier composed of plastic bears in a planar manner against the plate of the support body and extends over the plate of the support body via its appropriately designed edge in the manner of a clip. 
     A known grinding disc for a hand-held sander (EP 0 557 773 A1) includes a support plate composed of plastic, a cushion foamed onto the support plate as the carrier for a grinding means, and a steel disc located between them, as a reinforcing part. The underside of the cushion forms a flat mounting surface for an abrasive disc and is provided with Velcro strips, to which the velour backing of the abrasive disc adheres. The support plate includes, on its top side which faces away from the sanding cushion, a mounting surface enclosed by a centering ring for placing the grinding disc on an eccentrically driven driving element of an eccentric grinder. 
     To ensure that there is satisfactory running smoothness of the eccentric grinder, the eccentric component mass of the grinding disc is stabilized in a static and dynamic manner by at least one balancing mass attached to the output shaft of the electric motor. Since the magnitude of the balancing mass is matched to the mass of the grinding disc, only a certain single grinding disc may ever be used with the eccentric grinder. 
     SUMMARY OF THE INVENTION 
     The tool set according to the present invention—for an eccentric grinder has the advantage that, given that the disc mass has a fixedly specified value which is independent of the disc diameter that was selected, the grinding disc may be designed with different diameters in order to attain top-quality grinding results, and the grinding disc may be operated with the same eccentric grinder without this having a negative effect on the running smoothness of the machine. For example, it is possible to use a grinding disc with a disc diameter of 150 mm to grind large surface areas, and to use a grinding disc with a disc diameter of 125 mm to grind corners and concave surfaces in the same eccentric grinder. This provides customers with the advantage that they may use an entire set of grinding discs with the same eccentric grinder, the grinding discs having disc diameters which are specially adapted to the type of grinding work to be performed, while the machine maintains its same good handling quality at all times. 
     The value of the disc mass, which is fixedly specified by the balancing mass in the eccentric grinder, may be adhered to in different manners, independently of the disc diameter, e.g., according to an advantageous embodiment of the present invention, by designing the grinding disc with a height that is inversely proportional to the disc diameter, i.e., when the disc is manufactured with a large disc diameter, the disc height is made correspondingly small, and, conversely, when the grinding disc is manufactured with a small diameter, the disc height is made much greater. 
     According to an advantageous embodiment of the present invention, the grinding disc is composed of at least two components, a carrier plate for placement of the grinding disc on the eccentric of the eccentric grinder, and a sanding cushion fastened to the carrier plate with a supporting surface for a detachably connected abrasive disc. In this embodiment of the grinding disc, the specified value of the disc mass may be adhered to, independently of the disc diameter, by the fact that the density of the carrier plate material and/or the sanding cushion material are/is inversely proportional to the magnitude of the disc diameter. The grinding disc with a large diameter therefore has a grinding disc material with a lower density, and the grinding disc designed with a small disc diameter has a very large density. 
     According to an advantageous embodiment of the present invention, the fixedly specified value may also be adhered to, independently of the disc diameter, via various selections of the material of which the carrier plate and/or sanding cushion are/is composed. For example, a hard plastic may be used as the material for the carrier plate, and a plastic foam may be used for the sanding cushion, the density of the hard plastic being adapted to the disc diameter. As an alternative, it is possible to embed a metal ply in the hard plastic, the mass of which is inversely proportional to the magnitude of the disc diameter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention is described in greater detail in the description below with reference to an embodiment shown in the drawing. 
         FIG. 1  is a partial side view of an eccentric sander with a replaceable grinding disc, shown in a partial cross-sectional view, 
         FIG. 2  shows a tool set of two sanding discs—shown in a top view and in a sectional view along line A-A—with different diameters for the eccentric grinder in  FIG. 1 . 
     
    
    
       FIG. 1  shows a section, in a partial cross-sectional side view, of a hand-guided eccentric grinder which is referred to below as an eccentric sander, for performing grinding work. The eccentric sander includes a housing  11  which transitions into a handle  12  toward the left as shown in the illustration, on the underside of which a switch  13  is located for switching an electric motor  14  located inside housing  11  on and off. A wheel  16  of a suction fan is non-rotatably mounted on output shaft  15  of electric motor  14 , with which the sanding dust produced on the surface of a work piece during sanding work is suctioned up and transported via a blow-out connector  17  into a dust collection container. An eccentric recess  18  is provided in the hub of wheel  16 , which is penetrated by a driving element  19  which extends away from the underside of housing  11 , driving element  19  bearing via two roller bearings  20 ,  21  against the inner wall of eccentric recess  18 . Driving element  19  is driven in a rotating manner via roller bearings  20 ,  21 , depending on the bearing friction. Roller bearings  20 ,  21  and driving element  19  are retained in eccentric recess  18  in an axially non-displaceable manner. 
     A flat supporting surface  191  is formed on the underside of driving element  19 , on which a grinding disc  22  may be placed via a mounting surface  23  formed on its top side. The connection between grinding disc  22  and driving element  19  takes place via at least one cap screw  24 , which may be screwed into at least one axial borehole  192  formed in driving element  19 . A disc brake  25  composed of rubber is non-rotatably fastened to the underside of housing  11 . Disc brake  25  lies on the top side of grinding disc  22 . 
     Grinding disc  22  is composed of two components, a carrier plate  26  made of a hard plastic, and a sanding cushion  27  fastened to the underside of carrier plate  26 . Mounting surface  23  of grinding disc  22  is designed such that it is centered on carrier plate  26 . A supporting surface  271  for an abrasive disc (not depicted) is formed on the underside of sanding cushion  27  which faces away from carrier plate  26 . Supporting surface  271  includes a Velcro layer for fastening with the abrasive disc which has a velour backing. The Velcro layer is eliminated when self-adhesive sanding paper is used. Dust collection ports  29  which pass through carrier plate  26  and sanding cushion  27  are provided in grinding disc  22 , via which the sanding dust is suctioned into a dust collection chamber which is formed in housing  11  and connected to blow-out connector  17 , and in which wheel  16  rotates. To obtain a satisfactory running smoothness of the eccentric grinder, at least one balancing weight (not depicted) acts on output shaft  15  of electric motor  14 . The balancing weight neutralizes the eccentric mass of grinding disc  22  in a static and dynamic manner. The balancing weight may be realized, e.g., via a corresponding design of wheel  16  of the suction fan. The sum of the masses of the balancing weights that are present is referred to below as the balancing mass. 
     To attain top-quality sanding results when working with various work piece surfaces, it is advantageous to use grinding discs having grinding surfaces of different sizes, i.e., disc diameters of different sizes. For example, it is recommended to use a grinding disc with a disc diameter of 150 mm to grind large, flat work piece surfaces, and to use a grinding disc with a disc diameter of 125 mm to grind corners and concave surfaces. To be able to use grinding discs with such different disc diameters with the eccentric grinder shown in  FIG. 1  without altering the handling quality of the eccentric grinder—its running smoothness in particular—the disc mass of each grinding disc  22  has a fixedly specified value which is independent of the selected disc diameter. This value is specified by the balancing mass present in the eccentric grinder, which is matched to the imbalance-free operation of the eccentric grinder with a selected grinding disc  22  which is fastened to its driving element  19  and is covered with an abrasive disc. Grinding disc  22  is designed in a manner such that its center of mass lies on the disc axis at a comparable distance from mounting surface  23 , which is independent of the disc dimensions, i.e., the eccentric grinder always sees the same mass with a center of mass located in the same position, regardless of which grinding disc with which disc diameter is fastened to driving element  19 . 
     Various design-related measures are implemented individually or in combination in order to hold the disc mass of grinding disc  22  shown in  FIG. 2  constant, grinding disc  22  belonging to the tool set for the eccentric grinder shown in  FIG. 1 . For example, grinding discs  22  are manufactured in a manner such that the distance between mounting surface  23  and abrasive disc supporting surface  271  is inversely proportional to the disc diameter. As a result, grinding disc  22  which is shown on the left in  FIG. 2  and has the larger disc diameter has a markedly smaller axial disc height than does grinding disc  22  which is shown on the right in  FIG. 2  and has the smaller disc diameter. In addition or as an alternative thereto, the density of the material of carrier plates  26  is also inversely proportional to the magnitude of the disc diameter. For example, grinding disc  22  which is shown on the left in  FIG. 2  and has the larger disc diameter has a markedly smaller density than does the carrier plate material of the grinding disc which is shown on the right in  FIG. 2  and has the smaller disc diameter. 
     Carrier plate  26  of both grinding discs  22  is preferably made of hard plastic, and the density of the plastic material in both grinding discs  22  is selected to be equal, or the density of the hard plastic in grinding disc  22  with the larger diameter is selected to be smaller than the density of the hard plastic in grinding disc  22  with the smaller diameter. In the latter case, the material for sanding cushion  27  in both grinding discs  22  is made of plastic foam. 
     Although this is not depicted, a metal ply may be embedded in carrier plate  26 —which is composed of hard plastic—of each grinding disc  22 . The magnitude of the metal ply is inversely proportional to the magnitude of the disc diameter. For example, the material ply in grinding disc  22  which is shown on the right in  FIG. 2  and has the smaller diameter has a much larger mass than does the metal ply in grinding disc  22  which is shown on the left in  FIG. 2  and has a larger diameter. 
     In the two grinding discs  22  shown in  FIG. 2 , mounting surface  23  for placement of grinding disc  22  on supporting surface  191  of driving element  19  have the identical design. Dust collection ports  29  are adapted to the hole pattern of the abrasive disc specified for the disc diameter. Since the abrasive discs used in conjunction with grinding disc  22  having the larger diameter include a hole pattern with a total of six round holes, grinding disc  22  with the larger diameter therefore includes six oval dust collection ports  29  which are offset relative to each other by the same circumferential angle as are the abrasive disc holes, while sanding disc  22  with the smaller diameter includes a total of eight dust collection ports  29  with circular cross sections, which are distributed equally on a hole circle, in accordance with the hole pattern of the prescribed abrasive discs.