Patent Publication Number: US-6986627-B2

Title: Cylindrical bore head tool with hard metal cutters

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a cylindrical bore head tool with hard metal cutters. Hard metal cutters are desirable for cylindrical bore head tools or even necessary since bores, for example in the manufacture of furniture components, are cut into resin-bonded pressed particle boards so that tools of tool steels without hard metal cutters have only an unsatisfactory service life. 
   The manufacture of a cylindrical bore head with hard metal cutting edges however is complicated and expensive since it requires a bore tip as well as cutting edges extending over the front surface of the tool and also circumferential cutting edges in order to make clean, cylindrical bores. 
   It is the object of the present invention to provide a cylindrical bore head or a similar tool with hard metal cutting edges in such a way that it can be manufactured in large numbers at relatively low costs, but with high precision. 
   SUMMARY OF THE INVENTION 
   In a cylindrical cutter head tool including a shaft part with a cutter head support structure and a cutter head disposed on the cutter head support structure, the cutter head support structure with the shaft are an integral part made of tool steel and the cutter head is a sintered hard metal body, and the cutter head support structure and the cutter head include cooperating plate-like form-locking elements by which the cutter head is centered on the cutter head support structure and rotationally firmly engaged therewith. 
   The whole cylindrical cutter head, that is, the whole tool head consists of a hard metal which is formed by injection molding using a hard metal powder provided with a wax as plasticizer. The unfinished molded head is then sintered. The shaft with the cutter head support structure is made from a tool steel. 
   The hard metal cutter head and the head support structure are provided with cooperating form-locking elements by which the head is centered on the shaft when the head is mounted to the shaft and engages the shaft in a rotationally form-fitting relationship in such a way that the head has the proper rotational position with respect to the shaft and the head is rotationally locked to the shaft. The head and the shaft may then be interconnected by soldering or welding in a simple manner. 
   An embodiment of the invention will be described below in detail on the basis of the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a tool shaft with a head support structure in a perspective view, 
       FIG. 2  is a perspective view of a head as seen from the front end of the tool, and 
       FIG. 3  is a perspective view of the head as seen from the back side thereof. 
   

   DESCRIPTION OF A PREFERRED EMBODIMENT 
   The cylindrical bore head or cutter head tool according to the invention comprises a shaft  1  and a head  2  disposed on the shaft  1 . 
   As shown in  FIG. 1 , the shaft  1  comprises a shaft part  11  and a bore head support structure  12  disposed at the front end of the shaft part  11 . The bore head support structure  12  comprises two radial arms  13  in the form of sections of a disc. The bore head support structure is provided at its front face  14  with two axial surface projections  15 , one being provided on each of the radial arms  13 , and, furthermore, a central opening  16 . The shaft part  11  is cylindrical and serves for mounting the tool in a chuck. 
   The shaft part consists of tool steel. 
     FIGS. 2 and 3  show the head  2 , which is formed from hard metal as a single piece by injection molding from a hard metal powder mixed with a wax serving as a plasticizer and a bonding compound, and sintering of the unfinished molded piece. During sintering, the wax is completely removed. 
   The bore or cutting head  2  is provided at its front end with a bore head centering tip  21  and has two main cutting edges  22  extending radially in opposite directions and two precutters  23 , which are circumferentially displaced with respect to the cutting edges  22  by 90° and which provide for a circumferential precut of the bore to be cut. Such a cutter configuration is basically conventional. 
   At its rear side (FIG.  3 ), the cutting head has a central lug  24 , which fits into the central opening  16  of the shaft  1 . Furthermore, the head  2  is provided at its rear side with flat recesses  25  formed in the diametrically opposed radial disc sections at the front of which the cutting edges  22 ,  23  are provided. The flat recesses  25  are exactly complementary to the axial surface projections  15  of the bore head support structure  12  of the shaft part  1 . 
   The bore head  2  can be placed onto the bore head support structure  12  of the shaft  1  whereby the lug  24  at the rear side of the head  2  is snugly received as a centering lug in the opening  16  of the shaft and the surface projections  15  on the bore head support structure  12  of the shaft  1  are received in the flat recesses  25  at the rear side of the head. With this engagement, the head  2  is positioned with respect to the shaft in an exactly centered and rotational position correct manner and in such a way that it can be welded or soldered to the shaft in a simple manner without the need for providing particular holding or support devices for ensuring the accurate position of the parts to be joined during the welding or soldering procedure. Furthermore, the form-locking engagement ensures that operating torques are transmitted from the shaft to the cutting head by the form-fitting engagement and not by the solder or weld connection. 
   Obviously, the configuration of the bore head support structure  12  of the shaft  1  and of the bore head  2  can be different from the configuration as shown and also the form of the cooperating form-locking structure may be selected so as to be expedient for a particular application. 
   The shown arrangement for the interconnection of a cylindrical bore head with a shaft may also be used for other cutting tools which include a bore or cutting head supported on a shaft part for mounting in a chuck.