Abstract:
Provided is a hand-held electric cutting machine having excellent spark control capability, high stability, good usability and high versatility. A unit having: a first guard which covers a part of a disc-shaped cutting tool; a second guard which covers a part of the disc-shaped cutting tool and is rotatably attached to the first guard; a movable guard which is rotatable around outer peripheries of the first guard and the second guard, covers a part of the disc-shaped cutting tool, and is attached on the second guard; and a protector which covers an outside of the movable guard and is attached on the second guard, is attached to a hand-held electric tool serving as a driving source.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a hand-held electric cutting machine controlling sparks generated when a steel pipe, a steel sheet or the like is cut with a disc-shaped cutter. 
       BACKGROUND ART 
       [0002]    Generally, when machining a small-sized steel pipe, steel sheet or the like with a cutting grindstone, the machining work is often performed by a hand-held electric cutting machine represented by a disc grinder  1  with a dedicated guard  51  and base  52  attached thereto as shown in  FIG. 11 . Sparks  53  generated during the cutting, however, scatter in large quantity obliquely upward along the direction of rotation of a cutting grindstone  30  and, in the case of outdoor work, the flying sparks sometimes fall on an operator depending on the direction of wind. In addition, a part of sparks  54  sometimes passes by the inner periphery of the guard  51 , blows out from a rear end part  55 , bounces on the ground back to the operator, and possibly causes injury such as a burn to the operator depending on the situation. 
         [0003]    On the other hand, there are tip saws for metal generating a smaller quantity of sparks and enabling more highly-efficient cutting in the present market, but the tip saws cannot be used in the above-described hand-held electric cutting machine in terms of safety problem. 
         [0004]    In contrast, a circular saw described in Japanese Patent Laid-open Publication No. Hei 7-205101 can machine a steel pipe and a steel sheet using the above-described cutting grindstone or the tip saw for metal, in which a surface plate that is a part of its components stabilizes the cutting posture and a movable guard rotating about the rotational axis of a cutter exhibits, to a certain degree, an effect of preventing scattering of the sparks. However, there still remains a possibility that sparks flowing into a space between the inner periphery of the guard and the outer periphery of the movable guard blow out from a rear end part of the guard and bounce on the ground back to an operator as in the above-described disc grinder. 
         [0005]    Further, the front part of the cutter of the circular saw is widely open for exchange of the cutter and a large quantity of sparks scatters also from the front part. Moreover, since a pivot part for rotational movement of the movable guard is provided inside the guard, fine dust generated during the cutting, easily intrudes into the pivot part and consequently tends to cause failure of operation of the movable guard. 
         [0006]    In such a situation, in an example introduced in Japanese Patent Laid-open Publication No. 2002-283134, a cutter is nearly entirely covered with two sets of fixed covers and movable covers and is configured such that when the movable cover comes into contact with a work material, a part of the cutter is exposed from a slit on the cover and performs cutting, so as to prevent scattering of sparks. However, accumulation of the sparks inside the covers is not preferable in safety because of problem of ignition. 
         [0007]    Further, since the aforementioned example has a structure in which the cover on the side contacting the work material operates, there is no member, such as the above-described base or surface plate, which comes into contact with the work material and serves to stabilize the cutting posture, so that the operation becomes unstable and tends to apply load in an inappropriate direction with respect to the cutting grindstone and, as a result, to cause breakage of the cutting grindstone, thereby possibly bringing about a serious accident in which broken pieces scatter into an eye of the operator and lead the operator to blindness. 
         [0008]    On the other hand, in an example introduced in Japanese Registered Utility Model Publication No. 3008934, a movable guard having a rotational axis and moving to follow in a direction of discharge of sparks is provided at the front part of a cutter to prevent scattering of sparks. However, it is necessary to rotate the cutter and a work material in opposite directions in order to stabilize the cutting operation and the movement of a main body is limited to the rotational movement about a separately provided pivot, as described in this document, and therefore it should be said that its workability and general versatility is low. 
         [0009]    As described above, there has been no hand-held electric cutting machine, so far, which has high spark control capability and high stability for its operation, and is easy to use. 
       PRIOR ART DOCUMENT 
       [0010]    Patent Document 
         [0011]    Patent Document 1: Japanese Patent Laid-open Publication No. Hei 7-205101 
         [0012]    Patent Document 2: Japanese Patent Laid-open Publication No. 2002-283134 
         [0013]    Patent Document 3: Japanese Registered Utility Model Publication No. 3008934 
       DISCLOSURE OF THE INVENTION 
       [0014]    Problems to Be Solved by the Invention 
         [0015]    The hand-held electric cutting machines for machining steels, which have been designed so far, are not satisfactory, mainly because of safety problems such as control of sparks generated during cutting, stability of cutting operation. 
         [0016]    An object of the present invention is to solve the above-mentioned problems, and provide a hand-held electric cutting machine which has excellent spark control capability, high stability, good usability and high versatility. Means for Solving the problems 
         [0017]    The above object is achieved by attaching a unit having guards which cover a cutting tool, a movable guard which is rotatable around outer peripheries of the guards, and a protector which covers an outer periphery of the movable guard, to a hand-held electric cutting tool serving as a driving source. 
         [0018]    Effect of the Invention 
         [0019]    The hand-held electric cutting machine according to the present invention makes it possible to collectively discharge in a safe direction sparks generated during cutting of a steel and to make the cutting operation more stable and efficient. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]    [ FIG. 1 ] A perspective view showing an entire configuration of a hand-held electric cutting machine according to the present invention. 
           [0021]    [ FIG. 2 ] An exploded perspective view showing an internal configuration of the hand-held electric cutting machine according to the present invention. 
           [0022]    [ FIG. 3 ] A perspective view showing a bottom surface state of the hand-held electric cutting machine according to the present invention. 
           [0023]    [ FIG. 4 ] A partial sectional view of a side surface showing the internal configuration of the hand-held electric cutting machine according to the present invention. 
           [0024]    [ FIG. 5 ] A partial sectional view of a front surface showing the internal configuration of the hand-held electric cutting machine according to the present invention. 
           [0025]    [ FIG. 6 ] A perspective view showing a situation in exchanging a cutting tool of the hand-held electric cutting machine according to the present invention. 
           [0026]    [ FIG. 7 ] A partial sectional view of a side surface showing an embodiment of the hand-held electric cutting machine according to the present invention. 
           [0027]    [ FIG. 8 ] A perspective view and a partial top view showing the embodiment of the hand-held electric cutting machine according to the present invention. 
           [0028]    [ FIG. 9 ] A perspective view showing another embodiment of the hand-held electric cutting machine according to the present invention. 
           [0029]    [ FIG. 10 ] A perspective view showing examples of the cutting tool used in the hand-held electric cutting machine according to the present invention. 
           [0030]    [ FIG. 11 ] A perspective view and a partial sectional view of a side surface showing an example of a conventional hand-held electric cutting machine. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0031]    A hand-held electric cutting machine according to the present invention is configured such that a first guard  4  made of steel is attached to a guard attachment part  2  of a disc grinder  1  via a connector  3  as shown in  FIG. 1 , a second guard  5  made of steel is rotatably attached to the first guard  4  around a shaft  6  in a manner to cover the outer periphery of the first guard  4  as shown in  FIG. 2 , and a movable guard  7  made of steel and a protector  8  made of a transparent resin are attached on the second guard  5 . 
         [0032]    Further, as shown in  FIG. 3 , parts of the first guard  4 , the second guard  5 , and the protector  8  have edge parts made by being cut off along a plane, and when the respective members are combined, the edge parts form an edge surface  9  within the same plane. 
         [0033]    The movable guard  7  has a concentric shape covering the outer periphery of the second guard  5  and has a ring  10  for coupling provided at its central part. On the other hand, on the second guard  5 , a rotation base  11  having an outer diameter slightly smaller than an inner diameter of the ring  10  is fixed by welding to a central part thereof. In the state that the ring  10  is inserted into the rotation base  11  and a holder plate  12 , that is a separate member is set on an upper surface of the rotation base  11 , the protector  8  is fastened to the rotation base  11  by screws  13  together with the holder plate  12  and also fastened to the second guard  5  by screws  56 . 
         [0034]    In addition, as shown in  FIG. 4 , a spring  14  is set to follow the outer periphery of the ring  10  between the movable guard  7  and the second guard  5  and has one end attached to an attachment hole  15  on the movable guard  7  and the other end hooked on a hook  16  provided on the second guard  5 . Further, a stopper  17  is provided on the second guard  5  and comes into contact, at a predetermined position, with the movable guard  7 . 
         [0035]    In this case, as shown in  FIG. 5 , a gap  18  between the holder plate  12  and the rotation base  11  is set to be slightly larger than a ring width  19  so that the movable guard  7  can perform a smooth rotational movement around the center of the rotation base  11 , while being held on the second guard  5 . 
         [0036]    Windows  20  are provided at parts of side surfaces of the first guard  4  and the second guard  5 , and a first side protector  21  and a second side protector  22 , which are made of a transparent resin, are fixed on the respective windows by screws  23 . 
         [0037]    On a rear surface of a main body, a knob bolt  24  is fastened to a female screw  26  on the first guard  4  through a slit  25  provided on the protector  8  to indirectly fix the first guard  4  and the second guard  5 . 
         [0038]    By loosening the knob bolt  24  on the rear surface and then pulling up an operating lever  27  of the movable guard  7  as shown in  FIG. 6 , the second guard  5  and the movable guard  7  and the protector  8  simultaneously rotate around the shaft  6  in an interlocking manner to widely open the inside of the first guard  4 . In this state, by inserting a flange  28  into a spindle  29 , setting a cutting grindstone  30  on the flange  28 , and fastening a lock nut  31  to a male screw part  32  of the spindle  29 , the cutting grindstone  30  can be attached to the disc grinder  1 . 
         [0039]    For example, when a steel sheet is cut by the hand-held electric cutting machine according to the present invention, the disc grinder  1  is powered on first, and after it is confirmed that the cutting grindstone  30  has reached a certain rotational speed, a guide  33  provided on the first guard  4  is placed on a steel sheet  34  as shown in  FIG. 7 , and the disc grinder  1  is pressed forward as it is. Then, a head part  35  of the movable guard  7  comes into contact with the steel sheet  34 , its acting force rotates the movable guard  7 , and the cutting grindstone  30  thus exposed comes into contact with the steel sheet  34  and starts cutting. 
         [0040]    Sparks  37 , generated at a contact point  36  between the cutting grindstone  30  and the steel sheet  34 , scatter obliquely upward along the rotational direction of the cutting grindstone  30 , then come around behind along the side walls of the guards existing ahead, and flow out of a rear end part  38 . However, because the outer peripheral parts of the guards are covered with the movable guard  7 , all of the sparks  37  never leak to the outside but go around in the inner peripheral part of the movable guard  7 , and finally are collectively discharged from a tip end part  39  of the movable guard  7 . In this event, unlike the conventional product, the sparks  37  are discharged under the steel sheet  34  and are thus never allowed to fly, to a height where they may fall on the operator. 
         [0041]    When the cutting operation is proceeded as it is, an opening angle  40  of the movable guard  7  gradually increases and finally to nearly  180  degrees and the sparks  37  are discharged out of the rear end part  38  as in the conventional product. However, the position of the cutting grindstone  30  at that time has moved to a position far from the operator, so that there is a low risk. 
         [0042]    Once the cutting operation is ended and the steel sheet  34  is separated from the hand-held electric cutting machine, the movable guard  7  is instantaneously restored by the acting force of the spring  14  to the regular position where the movable guard  7  comes into contact with the stopper  17 . 
         [0043]    Unlike the aforementioned circular saw, the rotation base  11 , that is the pivot of the rotational movement of the movable guard  7 , is set outside the guard and the rotation base  11  is entirely covered with the protector  8  in the hand-held electric cutting machine according to the present invention, so that dust generated during the cutting is unlikely to enter a gap  41  between the rotation base  11  and the ring  10 , with the result that a functional capability for the smooth rotational movement of the movable guard  7  is maintained for a long time. 
         [0044]    Further, because the acting force of holding a work material between the cutting grindstone  30  and the guide  33  acts during the cutting operation, the hand-held electric cutting machine according to the present invention can keep a stable working posture and suppress the risk such as breakage or the like of the cutting grindstone  30 . Further, the edge parts of the guards and the protector form the edge surface  9  within the same plane as the bottom surface of the guide  33 , so that when the cutting is proceeded, the edge surface  9  continuously functions as a surface plate to keep the stable working posture. The stable working posture eliminates excessive energy loss and accordingly enables realization of smoother and more highly efficient cutting. 
         [0045]    When the operator wants to accurately cut a place of the work material, the operator can easily perform cutting on a cutting target line  43  by proceeding the cutting while aligning the center line of a cutout groove  42  with the cutting target line  43  because the center line of the cutout groove  42  provided in the guide  33  is configured to be aligned with the cutting position of the cutting grindstone  30 . 
         [0046]    Furthermore, it is possible to visually check the inside of the guard, in particular, a cutting edge part  44  of the cutting grindstone  30  over the first side protector  21  made of the transparent resin through the window  20  provided in the side surface of the first guard  4  as shown in  FIG. 8 , and therefore it is also possible to more sensuously target the cutting target line  43 . Note that since the scattering direction of the sparks is positioned nearly parallel with the surface provided with the window  20 , little or no sparks hit the window  20 , and the first side protector  21  covering the window  20  does not come to melt. 
         [0047]    When a material generating no sparks is cut by the hand-held electric cutting machine according to the present invention, the second side protector  22  attached to the side surface of the second guard  5  may be detached, a duct connector  45  shown in  FIG. 9  may be attached instead, and a hose  46  of a dust collector (not shown in Figures) is connected to the duct connector  45 , thereby enabling collection of dust and chips generated during the cutting when necessary. 
         [0048]    Note that the aforesaid material generating no sparks means, for example, wood material, gypsum board, concrete or the like, and when machining these materials, various kinds of cutting tools such as a tip saw  47  and a diamond cutter  48  as shown in  FIG. 10  can be selectively used depending on usage in place of the cutting grindstone  30 , because the safety of the hand-held electric cutting machine according to the present invention is ensured by employing the movable guard  7 . 
         [0049]    The protector  8  covers the outer periphery of the movable guard  7  to prevent the operator from mistakenly touching with the movable guard  7 , which performs rotational movement on the outer peripheries of the guards and also provides a function of isolating the operator from the guards made of steel generating heat during the operation so as to reduce the risk of burn or the like. Similarly, the fastening part of each screw is designed to the operator away from the screw part generating heat by providing a wall shape  49  at the peripheral part of a hole for attaching the screw of the protector. 
         [0050]    The connector  3  attached to the first guard  4  may be freely exchanged with the one having another shape by removing fixing screws  50  at three positions, and thereby attachable to various types of disc grinders. 
         [0051]    Note that though the materials of the guards and the protector are described in the above, it is not always necessary to employ the materials designated in this document, depending on an object work material and the kind of cutter. The mechanisms of the first guard  4 , the second guard  5 , and the movable guard  7  are not limited to the rotational type introduced in this document, but another mechanism such as a detachable type may be employed. Further, the components illustrated in the above embodiment may be composed in an integrally molded type unless otherwise there is no technical and strength problems. 
         [0052]    Explanation of Codes 
         [0053]      1  disc grinder 
         [0054]      2  guard attachment part 
         [0055]      3  connector 
         [0056]      4  first guard 
         [0057]      5  second guard 
         [0058]      6  shaft 
         [0059]      7  movable guard 
         [0060]      8  protector 
         [0061]      9  edge surface 
         [0062]      10  ring 
         [0063]      11  rotation base 
         [0064]      12  holder plate 
         [0065]      13  screw 
         [0066]      14  spring 
         [0067]      15  attachment hole 
         [0068]      16  hook 
         [0069]      17  stopper 
         [0070]      18  gap 
         [0071]      19  ring width 
         [0072]      20  window 
         [0073]      21  first side protector 
         [0074]      22  second side protector 
         [0075]      23  screw 
         [0076]      24  knob bolt 
         [0077]      25  slit 
         [0078]      26  female screw 
         [0079]      27  operating lever 
         [0080]      28  flange 
         [0081]      29  spindle 
         [0082]      30  cutting grindstone 
         [0083]      31  lock nut 
         [0084]      32  male screw part 
         [0085]      33  guide 
         [0086]      34  steel sheet 
         [0087]      35  head part 
         [0088]      36  contact point 
         [0089]      37  spark 
         [0090]      38  rear end part 
         [0091]      39  tip end part 
         [0092]      40  opening angle 
         [0093]      41  gap 
         [0094]      42  cutout groove 
         [0095]      43  cutting target line 
         [0096]      44  cutting edge part 
         [0097]      45  duct connector 
         [0098]      46  hose 
         [0099]      47  tip saw 
         [0100]      48  diamond cutter 
         [0101]      49  wall shape 
         [0102]      50  fixing screw 
         [0103]      51  guard 
         [0104]      52  base 
         [0105]      53  spark 
         [0106]      54  spark 
         [0107]      55  rear end part 
         [0108]      56  screw