PATENT ABSTRACT
A cutter for milling of workpiece includes a cutter body, a first cutting portion, and a second cutting portion formed between the cutter body and the first cutting portion. The first cutting portion carries out primary machining on the workpiece. The first and second cutting portions extend in opposite twists or helixes along a central axis of the cutter body and are rotated in opposite directions during machining.

PATENT DESCRIPTION
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates generally to a milling cutter and, more particularly, to a milling cutter, which is capable of performing rough or primary machining and precision machining at the same time. 
         [0003]    2. Description of Related Art 
         [0004]    In milling, a plurality of burrs may be generated by a milling cutter. To obtain a surface with high quality on a workpiece, the workpiece may require another machining process and another cutter for removing the burrs. During the two machining processes in milling, the first and second milling cutters must be exchanged, and a position of the second milling cutter used must be adjusted to find a proper starting point or work point. Thus, milling is performed by alternating between using the different (first and second) milling cutters, and adjusting the positions of the milling cutters, which takes or consumes more time, thereby decreasing the overall working efficiency and the working precision. 
         [0005]    Therefore, there is room for improvement within the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The elements in the drawings are not necessarily drawn to scale, the emphasis instead placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0007]      FIG. 1  is an isometric view of an embodiment of a cutter having a cutting portion. 
           [0008]      FIG. 2  is similar to  FIG. 1 , but viewed from another aspect. 
           [0009]      FIG. 3  is an enlarged view of a circular part II of  FIG. 1   
           [0010]      FIG. 4  is a top plan view of an end of the cutting portion of the cutter of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  shows an embodiment of a cutter  100 . The cutter  100  includes a cutter body  10 , a cutter handle  30 , and a cutting portion  50 . The cutter handle  30  and the cutting portion  50  are formed at opposite ends of the cutter body  10 . 
         [0012]    In the illustrated embodiment, the cutter body  10  is substantially cylindrical, and defines a central axis α. In machining, the cutter body  10  rotates about the central axis α. The cutter body  10  includes a first end  12  and a second end  14  formed at an end of the first end  12 . The cutting portion  50  is formed at the first end  12  of the cutter body  10 , and the cutter handle  30  is formed at the second end  14  of the cutter body  10 . 
         [0013]    The cutter handle  30  can have a straight shank or a tapered shank. The cutter handle  30  is used for attaching the cutter  100  to a main shaft (not shown) of a computer numerical control machine (not shown). 
         [0014]    The cutting portion  50  includes a first cutting portion  60  and a second cutting portion  70  connected to the first cutting portion  60 . The first cutting portion  60 , the second cutting portion  70 , and the cutter body  10  are aligned along the central axis α. The first cutting portion  60  is adjacent to the second cutting portion  70  along the central axis α. The first cutting portion  60  extends toward the cutter handle  30  in a helix shape along the central axis α of the cutter body  10 . The second cutting portion  70  extends toward the cutter handle  30  along the central axis α of the cutter body  10  in a helix shape. In the illustrated embodiment, a helical direction of the first cutting portion  60  and a helical direction of the second cutting portion  70  are opposite of each other. A distance between the first cutting portion  60  and the cutter body  10  is greater than a distance between the second cutting portion  70  and the cutter body  10 . A length of the first cutting portion  60  along the central axis α is equal to or slightly smaller than a length of the second cutting portion  70  along the central axis α. The first cutting portion  60  is used for the rough or primary machining of a workpiece (not shown), and the second cutting portion  70  removes burrs being created on the portion of the workpiece which has been cut during the primary milling performed by the first cutting portion  60 . 
         [0015]    Referring to  FIGS. 2 through 4 , the first cutting portion  60  includes two lead cutting edges  61  and two side cutting edges  65 . The two lead cutting edges  61  and the two side cutting edges  65  are alternately arranged in an end surface of the first cutting portion  60  along a circumferential direction of the first cutting portion  60 , and helically extend toward the cutter handle  30  along the central axis α. A first helical groove  66  is defined between one of the two lead cutting edges  61  and one of the two side cutting edges  65  next to the lead cutting edge  61 , to facilitate the discharge of metal chips and dissipation of heat produced in machining process. Each of the two lead cutting edges  61  includes an end edge  612  in an end surface thereof, and a circumferential edge  614  connected to the end edge  612 . The end edge  612  is substantially straight. The circumferential edge  614  extends helically along the central axis α. The side cutting edge  65  includes an end edge  652  and a circumferential edge  654  connected to the end edge  652 . A cutting edge radius of the end edge  652  of the side cutting edge  65  is equal to or slightly greater than a cutting edge radius of the end edge  612  of the lead cutting edge  61 . As such, the end edge  612  is used for primary machining, and the end edge  652  is used for precision machining. The circumferential edge  654  has the same structure as that of the circumferential edge  614  of the lead cutting edge  61 . 
         [0016]    The second cutting portion  70  includes a first cutting edge  71 , a second cutting edge  73 , a third cutting edge  75 , and a fourth cutting edge  77 . The four cutting edges  71 ,  73 ,  75 ,  77  helically extend from the first end  12  of the cutter body  10  along the central axis α. The first cutting edge  71  is adjacent to the second cutting edge  73 . A first cutting end edge  711  is formed between the first cutting edge  71  and the second cutting edge  73 , and is adjacent to one first helical groove  66 . The third cutting edge  75  is located adjacent to the fourth cutting edge  77 . A second cutting end edge  713  located opposite to the first cutting end edge  711  is formed between the third cutting edge  71  and the fourth cutting edge  77 , and is adjacent to another first helical groove  66 . In the machining process, the first cutting end edge  711  and the second cutting end edge  713  are capable of removing the burrs created by the two lead cutting edges  61  and the two side cutting edges  65  of the first cutting portion  60 , along a cutting direction thereof. 
         [0017]    During machining, the cutter  100  rotates along the central axis α. Because the direction of twist of the second cutting portion  70  is opposite to the direction of twist of the first cutting portion  60 , and the cutting direction which is applied to the second cutting portion  70  is the reverse cutting direction when burrs were generated, and the burrs created are removed by the second cutting portion  70 . The processes of having to alternating cutter installation for usage or the re-positioning the workpiece upon installation of a new cutter are simply not needed, such that labour hours can be greatly decreased, and the working efficiency is increased. Further, any error introduced by having to re-position the second cutter can be avoided, and the working precision for milling can be greatly increased. 
         [0018]    The quantities of the lead cutting edges  61  and of the side cutting edges  65 , respectively, of the first cutting portion  60  can be changed according to a size or the manufacturing difficulty of the cutter  100 , for example, the total number of the lead cutting edges  61  or the side cutting edges  65  can be two, or four, or eight. The lead cutting edges  61  and the side cutting edges  65  can be arranged non-uniformly in the end surface of the first cutting portion  60  along the circumferential direction thereof. Shapes of the lead cutting edge  61  and the side cutting edge  65  can be changed according to a surface shape of the workpiece to be machined. 
         [0019]    It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages.