Abstract:
A hand-held belt sander has a housing, an on-off switch and a power supply conductor supported by the housing, a motor and a transmission received in the housing, a sanding belt, a driving roller driven by the motor and driving the sanding belt, a sliding shoe provided with a base, a deviating roller arranged so that said sanding belt is guidable over the deviating roller and the base of the sliding shoe, a unit for centering the sanding belt, a unit for clamping the sanding belt, the deviating roller and the driving roller have different diameters so that the sanding belt is guided inclinedly, the housing being elongated and the sanding belt being guided on guiding parts which are introduced in a rear region of the elongated housing so that with together with the sanding belt in a front region of the elongated housing a centrally forwardly extending, freely projecting, wedge tip-shaped contour is formed so that the hand-held belt sander as a whole has a lance-like contour.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a hand-held belt sander.  
           [0002]    Hand-held belt sanders are known in the art. One of such hand held belt sanders is disclosed in the U.S. Pat. No. 4,694,616. It is provided with a driving roller and two deviating rollers having a substantially corresponding diameter. They guide the sanding belt over a sanding base exchangeably arranged on the device. With this device small surfaces of various profiles can be well treated. However, because of the relatively great diameter of the driving and deviating rollers of the hand-held belt sander and because of the coinciding tangential transmission between the rollers and the sanding base, corners and hollow channels are not sufficiently accessible.  
           [0003]    The German patent document DE 02 42 26 708 discloses a stationary belt sanding machine with a sanding belt guided over at least two rollers and having a small sanding base. It is provided for sanding works, in which work pieces are to be treated only directly over the sanding belt surface in the embracing region of the rollers, in particular for the production of concave surfaces.  
           [0004]    The German patent document DE 0S 39 19 651 discloses a handheld belt sander which in addition to the conventional substantially identical deviating and driving rollers, has a small additional deviating roller for guiding the sanding band tangentially coincidentally between the deviating roller and the sanding base. With this device, corners and hollow channels are substantially better accessible than with other handheld sanders. Since however its construction is based on the conventional handheld belt sander, its belt centering and belt tensioning can be performed in expensive way because of additional, small deviating roller.  
           [0005]    Furthermore, the British patent document GB 962 164 discloses a handheld belt sander with the driving roller provided on its periphery with longitudinal grooves. Therefore an improved for transmission to the sanding band is obtained. The handheld belt sander is however heavy, uncomfortable, and complicated.  
           [0006]    In the known handheld belt sanders the belt centering is performed by turning or tilting of the deviating rollers which rotate on roller or metal sliding bearings about a fixed rotary point on the roller axis. The deviating roller is mounted by screwing or safety rings on its axle. An exchange of the deviating roller is complicated. Moreover, in the known belt sanding devices the sanding band is tensioned by displacement of an operating lever which is operative for actuating the deviating rollers at the outer side of the sanding belt. However, the operating lever is difficult to axis and not easy to operate.  
           [0007]    In belt sanders, independently from their size of the width of the belt, the sanding belt is driven through a rotatable driving roller by a frictional connection. Therefore, the force transmitted to the belt is dependent on the friction value between the inner side of the belt and the roller, as well as on the normal force of the belt on the roller, and on the embracing angle. However, in the known belt sanders these values are not sufficient.  
         SUMMARY OF THE INVENTION  
         [0008]    Accordingly, it is an object of present invention to provide a handheld belt sander which avoids the disadvantages of the prior art.  
           [0009]    In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a hand-held belt sander which has a lance-shaped contour, and in which the parts which guide the sanding band are guidingly introduced in a rear region of an elongated housing so that, together with the sanding belt they form in the front region of the housing a centrally forwardly extending, freely projecting wedge-tip shaped contour.  
           [0010]    When the hand-held belt sander is designed in accordance with present invention, it has better handling, simplified mechanical system for manual adjustment of a belt centering, as well as is favorable as to the number of individual parts, the manufacture and mounting.  
           [0011]    In accordance with another feature of present invention, a fork which receives the deviating roller and which is used for adjustment of the belt running can be exchangeable by a user without dismounting the parts of the device.  
           [0012]    A further advantage of the present invention is that the belt running is centerable with a handle which surrounds the roller axis of the deviating roller at both sides and is supported in a sliding member so that it is joined through a virtual three point structure and is tiltable around it with an adjusting screw. The legs of the handle are formed as flat springs which by the screw force both fix the roller and also are used for a special position of the sliding block. The handle is supported at the rear end centrally in the sliding member, so that no high moments are produced in the lever. The small deviating rollers which are arranged in pairs near one another for the belt are composed of high-strength synthetic plastic and run with self lubrication and without additional roller or sliding bearings directly on the roller axle. A substantially simplified mounting, lower number of components, and low cost, as well as a simpler subsequent change of the deviating rollers is characteristic for the inventive solution when compared with the known solutions.  
           [0013]    A special advantage of the inventive hand-held belt sander is that the sanding belt can be easily exchangeable by unlocking of both clamping rollers with a single lever which is easily operable and arranged outside of the device. The both clamping rollers are supported so that they are elastically coupled with one another to be outwardly radially expandable. In the locked position this provides for the elastic sufficient belt clamping. The adherence of the sanding dust is prevented by the clamping rollers. The clamping lever is designed so that both in the blocked and in the unblocked position it engages in a simple manner without additional components for arresting its rotary axle.  
           [0014]    A further advantage is that a fixed base plate of the belt clamping mechanism and the sanding shoe, as well as other parts are held premountable before the mounting in the ridge-like manner. In addition, the base plate which works as a supporting cover has further functions such that the receipt of the roller bearing of the drive shaft which carries the driving roller and the receipt end positioning of the buffer disk. The bearing support is formed as a simple punched part for all multiple functions. Since its mounting is performed without additional parts between the sliding shoe and the housing shell, only a few individual components are and the mounting is simplified. A further advantage of the invention is that the frictional connection of the driving roller relative to the sanding belt is increased by combining the running surface of the driving rollerfrom hard and soft material and applying grain material on the running surface, or it is provided with brushes and the normal force between the sanding belt and the driving roller is increased by forming grooves in the running layer, so that inclined small plates are formed which are placed under load and thereby increase in diameter of the roller. Furthermore, the application of a skin-like coating has the advantage that under load it rises, and an additional pressing roller is arranged, so that with no raising the clamping force of the belt is needed and the sanding belt can be finally operated.  
           [0015]    It is also advantageous to provide a form-locking connection between the belt and the roller, by combining a perforated belt with a roller provided with pins or by profiling the lower side of the belt and the roller so that a form-locking connection is produced during roller of this parts over one another. In corresponding variants, the advantage of a form-locking drive is provided by a transmitting correspondingly high forces with relatively low belt clamping.  
           [0016]    Therefore the sanding shoe, the drive cover, the housing and the means for belt clamping are provided with inventive features, and the sanding shoe and the drive cover form an important component of a replacement part, on which a differently equipped sanding belts or the like can be arranged.  
           [0017]    The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a spacial view of a hand-held belt sander in accordance with one embodiment of the, present invention;  
         [0019]    [0019]FIG. 2 is a spacial, partially exploded view of a front region of the inventive hand-held belt sander with a released sanding belt;  
         [0020]    [0020]FIG. 3 is an explosion view of the inventive hand-held belt sander;  
         [0021]    [0021]FIG. 4 is an explosion view while FIGS.  5 - 8  are side views of a transmission cover and a belt clamping axial;  
         [0022]    [0022]FIG. 9 is a view of a front region of the hand-held belt sander from the side of the clamping and loosening lever for sanding belt exchange;  
         [0023]    [0023]FIG. 10 is a view showing a longitudinal section of the front region of the hand-held belt sander;  
         [0024]    [0024]FIG. 11 is a view of the front region of the hand-held belt sander from the side of the free sanding belt side;  
         [0025]    [0025]FIGS. 12, 13 are a longitudinal and a transverse section of the clamping and loosening lever;  
         [0026]    [0026]FIGS. 14 a  and  14   b  are views showing a transverse cross-section of the driving roller;  
         [0027]    [0027]FIGS. 15 a  and  15   b  are views showing a further modification of the driving roller;  
         [0028]    [0028]FIG. 16 is a spacial view of a sliding shoe; and  
         [0029]    [0029]FIGS. 16 a  and  16   b  are views showing an auxiliary tool for exchanging deviating rollers.  
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0030]    A hand-held belt sander  10  shown in FIG. 1 has a slim, lance-shaped construction with forward wedge-shaped and approximately tip-shaped working surfaces of a sanding band  20 . Its housing  12  extends directly rearwardly for receiving a transmission  15  and a motor  14  shown in FIG. 3. The elongated, rod-shaped housing  12  includes a longer and a shorter shells  112 ,  212 , which are connected with one another through a central abutment joint  312 .  
         [0031]    An on-off switch  16  is arranged in the rear region of the housing  12  for turning on the motor for rotating the sanding belt  20 . An electric cable  18  extends from the rear end of the housing  12 . Near it a suction  2101  of the suction passage  101  shown in FIG. 3 near an adjusting gear  105  of an electronic rotary speed preselecting device. Lateral ventilation slots  106  are provided in the rear and the front region of the housing  12 . The shorter shell  212  forms relative to the longer shell  112  a recess  412  in the wedge-shaped, front region of the housing  12 . A sanding belt  20  is guided in the recess  4102  so that it substantially coincides with the contour of the elongated shell  112  as seen in the lateral direction.  
         [0032]    The sanding belt  20  is supported by a sliding shoe  33  shown in FIG. 3. The sliding shoe is wedge-shaped and has a tip  333  extending forwardly. The sliding shoe  33  is provided on its edge surfaces with two sanding bases  133 ,  233 . The sliding shoe in front of its tip  333  carries on a handle  33  with the fork  35 , a pair of deviating rollers  31 . The deviating rollers pair  31  is rotatably supported in the fork  35  through an axial  32  as shown in FIG. 3. At the opposite side of the deviating roller pair  31 , the sanding belt  20  is guided over a driving roller  46  shown in FIG. 3. A housing axis  510  identified in a dot-dash line illustrates the longitudinal extension of the hand-held belt sander  10 .  
         [0033]    A turning button  139  for adjusting a centering position of the sanding belt  20  is arranged in the front region of the longer housing shell  112 . It projects laterally and is integrated by arrangement in an indentation flush in the housing contour. During turning of the button  132  the fork  35  with the axial  32  and the handle  34  which carries the deviating rollers  31  is turned, depending on a rotary direction, in one or another direction.  
         [0034]    Closely near the turning button  139 , the hand-held belt sander  10  carries a clamping and releasing lever  51  which projects laterally and is also integrated in the housing contour by arrangement in an indentation and flush with it. During turning of the clamping and releasing lever  51  about its axis  511 , the sanding belt  20  is released for exchange.  
         [0035]    A suction hose  103  is connectable to the suction pipe  2101 . The suction hose is connected with an external, not shown dust aspirating device for aspiration of sanding dust.  
         [0036]    An auxiliary handle  110  with its threaded piece  111  is screwable into a threaded opening  108  in the front region of the longer shell  112  of the housing  12 . Thereby the hand-held belt sander  10  can be adjustable in an especially fine and controllable manner.  
         [0037]    [0037]FIG. 2 shows the hand-held belt sander  10  with a dismounted sanding belt  20  and the clamping lever  51  located in its releasing position in which it is turned downwardly. The deviating rollers  31  which are arranged in pair, the sliding shoe  33  together with the sanding bases  133 ,  223  and the radially inwardly turned clamping roller  47  can be clearly seen from this Figure.  
         [0038]    [0038]FIG. 3 shows a hand-held belt sander  10  in an explosion view. Its construction, its components and its operation can be easily recognizable. These figures specifically shows the housing  12  assembled of the longer and shorter shells  112 ,  212  and forming a recess for  112  in the front region in view of their length difference.  
         [0039]    A small pinion  215  which is not shown in detail supports a roller bearing and axially following impeller, and a partially shown roller of the motor  14  is connected to it. The small pinion  21  engages with the plate gear  115  of the transmission  15 , which is surrounded by a lubricant  1098  and is centrally fixably connected with a driven shaft  91 . The species  16  is held between the shelves  112 ,  212 . The E-connecting cable  18  extending outwardly of the housing  12  is also held between the shells.  
         [0040]    The sanding belt  20  can be seen at the left side in the observation direction, and the sanding basis  133 ,  223  with the felt plates  43  arranged under them are located above the sanding belt. The deviating roller pair  31  with their axial  32  which carries at its ends pins  132  are shown above at the left side. Furthermore, the sliding shoe  33  with its tip  333  follows the handle  34  with the fork  35  at the right side. Its opening  44  merging into slot  533  and bore hose  331   332  can be easily seen in this Figure. The fork  34  in the mounted condition surrounds the sliding shoe  33  in a springy gap-free manner.  
         [0041]    The handle  34  carries a bent tab  235  with an opening  135  for passage of an adjustment screw  39 . It is supported by spring  335  on the bottom of the opening  44 . The screw  39  is adjustable by an adjusting button  139  and operates for turning the handle  34  together with the deviating rollers  31  for centering of the belt running.  
         [0042]    The design and the operation of the rear end  37  of the handle  34  is illustrated in FIG. 10. This Figure also shows radii  38 ,  41  in the groove button  40  of the slot  533  for guiding the fork  35 , which form a virtual rotary point  42  for the handle  44 .  
         [0043]    The driving roller  46  shown in the upper, central region in FIGS. 3 and 4 has small plates  146  which are separated from one another by inclined slots  246 . Belt clamping rollers  47 ,  48  composed of synthetic plastic material are shown at the left side. By turning of the supporting lever  52 ,  53  they are movable readily inwardly by means of the clamping and releasing lever  51  for exchanging the sanding belt  20 .  
         [0044]    FIGS.  5 - 12  show the operation of the components illustrated in FIGS. 3 and 4. They include a plug  54  which projects on a lateral arm of the supporting lever  52  axis-parallel with it, a spring wire  55 , the transmission cover  57 , the torsion spring  59 , the pin  60  with the end  61 ,  62 , a release  63  in the transmission cover  57 , a U-shaped clamping spring  64  with ears  65 ,  66 , a reap  68 , an axial plug  69 , a longitudinal opening  70 , a flat spring  71  in the clamping-releasing lever  51 , its ends  72 ,  75 , grooves  73 ,  74 , an axial  76  of the clamping-releasing lever  51 , a slot  77  in the axial  76  of the clamping-releasing lever  51 , a longitudinal cortigation  78  in the flat spring  71 , transverse grooves  79  in the belt clamping rollers  47 ,  48 , a pin  82  on the transmission cover  57  which forms the axis of the bearing lever  52 , a pin  182  which forms an axis for the bearing lever  53 , openings  282 ,  382  in the bearing levers  53 ,  52 , a circular-arc-shaped punch out  83  in the transmission cover, openings  85  a collar  86 , a needle bearing  87  for the driven shaft  91 , the release  88 , claws  89  forming an axial securing feature for the disk  22  of ceramic, a housing plug  90 , a profiled plug  93  of the adjusting plate  94  for the transmission gap adjustment, a plug  193  for floating the profiled plug  93 , a fixed bearing  95 , an arresting projection  96 , axial grooves  97 , a lubricant pen  98 , an outer wall  99  of the housing, a ring wedge  1  housing, a suction opening  1101  of the dust aspiration passage  101 , a suction pipe  2101  a threaded opening  102  in the sliding shoe  33  for an engagement of a holding screw of an underframe for mounting on the sliding shoe, both openings  1102  in the sliding shoe  33  for engaging of the plug of a not shown underframe for a stationary arrangement of the hand-held belt center  10 .  
         [0045]    As can be seen from FIGS.  5 - 8 , bearing levers  52 ,  53  are provided for mounting the rollers  47 ,  48 . The rollers can turn on the bearing levers over a circular path radially inwardly. The rollers  47 ,  48  are turned inwardly as shown in FIGS. 2, 11, for a belt exchange. In the operational position the roller  48  is mechanically arrested in its outer position, while the other roller  47  is pressed outwardly by a spring  59 . The fixedly arrested roller  48  abuts against a side of the sander, on which the sanding band  20  is inserted in the housing  12 . Thereby, independently on the belt length, a constant inlet gap  49  of less 6 mm between the running in belt  20  and the housing edge  50  is guaranteed for safety reasons. Thicker sanding bands lead however to smaller gaps. Both rollers  47 ,  48  or bearing levers  52 ,  53  are simultaneously actuated through a clamping/releasing lever  51  arranged outwardly on the housing  12 . For this purpose the bearing lever  52  which actuated directly through the clamping-releasing lever  51  is connected through an axial plug  54  on which a spring-wire piece  56  with an ear  56  is mounted as shown in FIG. 4. A sliding down of the wire  55  from the plug  54  is prevented since the free end of the plug  54  after mounting of the lever  52  ends directly over the upper surface of the bearing cover  57 . The other end of the wire  55  is mounted in the same way on the other bearing lever  53 . The engaging points  54 ,  58  of the wire ends at both bearing levers  52 ,  53  are selected so that during turning of the directly driven bearing lever  52  its plug  54  is moved outwardly forwardly and a pulling tensioning is produced in the connected spring wire  55 . This generates on the second bearing lever  53  a moment which turns the bearing lever  53  and thereby the second belt clamping roller  57  also inwardly. Since the directly driven bearing lever  52  in the clamping position assumes a defined position, while the other bearing lever  53  is deviated more or less due to the spring force independence on the belt length and thickness, the spring wire  55  between the lever  52 ,  53  is angled so that a certain displacement between the engaging points is possible.  
         [0046]    The bending angle and the wire length are selected so that despite the permissible displacement compensation, the driving operation of the spring wire  55  is not negatively affected. The application of the clamping force to the not directly actuated bearing lever  53  is performed through a torsion spring  59 . This spring is held on a pin  60  on the transmission cover  57  and its one end  61  is supported against a formation  63  in the transmission cover  57  and pressed by it simultaneously against the transmission cover  57 , so that the torsion spring  59  can not spring from the pin, while the other end  62  is supported on the axial  58  of the second clamping roller  47  and presses it thereby outwardly. Therefore, no additional components are needed for mounting of the spring  59 .  
         [0047]    The blocking of the clamping mechanism in the clamping position is performed through a U-shaped clamping spring  64  with two ears  65 ,  66  on its ends. One ear  66  surrounds the rotary axial of the directly actuated bearing lever  52 , while the other ear  65  surrounds the extension of the axial  67  of the directly actuated clamping roller  48 . The spring  64  is formed so that during the blocking process it slides with one corner on an inwardly projecting rib  68  of the housing  12  and therefore is deformed. At the end of the actuation path of the directly actuated bearing lever  52 , the spring can snap under the rib  68  and thereby to block the mechanism against a reverse turning. The unblocking of the mechanism is performed by the clamping/releasing lever  51  which has an axial plug  69  engaging in the U-shaped spring  64 . During the actuation of the releasing lever  51 , first the blocking spring  64  is pressed by the plug  69  laterally, before the bearing lever  52  is turned. In order to prevent a direct co-rotation of the bearing lever  52  so that the forces on the bearing lever  52  do not unblock the blocking spring  64  by the clamping/releasing lever  51 , the clamping/releasing lever is connected with a certain slack which is formed by an elongated hole  70  on the receptacle of the extension of the clamping roller axial  67 . Thereby the mechanism can be unblocked by hand only by actuation of the lever  51 . FIG. 9 shows a front region of the hand held belt sander  10  from the side of the longer shell  112 . The turnable fork  35  of the handle  34  is supported at both sides on the concavely curved wall of the sliding shoe  33  which guides it as a supporting surface  39 . One of the two neighboring deviating rollers  31  can be seen in the drawing. An especial bearing for the deviating roller  31  is dispensed with, since they are composed of a special, high-grade synthetic plastic and run without lubrication on the axial  32 . The deviating rollers  31  can have a diameter of smaller than 8 mm. The pins  132  at the ends of the axial  32  engage in the openings of the fork  35 . For mounting of the axial  32  in the fork  35 , it is easily elastically bendable by an auxiliary tool manually. Subsequent, the axial  32  provided with the rollers  31  can be inserted. After this the fork  35  is compressed, the axial  32  is reliably clamped and is under slide pretensioning. The fork  35  acts simultaneously as a flat spring. Thereby the axial  32  and the rollers  31  can be exchanged with dismounting of the sliding shoe  33  or the hand held belt sander  10 .  
         [0048]    [0048]FIG. 17 a  and  17   b  show the auxiliary tool  36  for easy exchange of the deviating rollers  31 , for example in the case of wear. The tool  36  is an elongated, flat, synthetic plastic part which surrounds a side of the form  35 . It is supported in an immediate proximity outside on the sliding shoe  33 , runs with an engagement edge between the inner edge of the handle  35  and the end of the deviating roller  31 , and over a long lever  136  a convenient elastic bending of the form  35  with only hand is performed. Thereby, the roller  31  and the axial  32  can be easily withdrawn and exchanged.  
         [0049]    [0049]FIG. 11 shows that for both-side axial support of the axial  32 , the handle  34  carries the fork  35  and is supported centrally with the opposite ends  37  in the sliding shoe  33 . For fixing of its lateral position relative to the sliding shoe  33 , the form  35  is curved inwardly concavely with the same curvature radius corresponding to that of the supporting surface  38  of the sliding shoe  33 . The design of the fork  35  as a pretensioned flat spring permits the construction of the abutment surfaces  38  of the sliding shoe  33  so that the fork  35  during turning relative to the supporting surface  38  must be slightly bent and thereby spring against the abutment surface  38 . Therefore, it sits without a gap in the sliding shoe  33 . The tilting of the total handle  34  for the belt running centering is performed by means of an adjusting screw  39 , manually with the rotary button  139 . It engages with the rear end  37  of the handle  34  and its axis is approximately parallel to the axis  32  of the deviating rollers  31 . The rear end  37  of the handle  34  is turnable by the adjusting screw  39 , and it is fixable in all degrees. During adjustment the end  37  of the handle  34  slightly slides against the rear support  40  which is formed in the groove bottom of the slot  633 . The radius  41  at the end  47  of the fork  35  is formed so that its central point is located in the virtual turning point  42  of the handle  34 , which is identical with the center points of the radii of the supporting surface  38  in the slide shoe  33  over the fork  35 . With another selection of the radius at the end  37  varying rotary points are provided during the adjustment.  
         [0050]    For fixing the rotary point  42  no special axle is needed, in contrast to the known solution. Moreover, with the corresponding construction of the operational surfaces in the sliding shoe  33 , no special guiding parts are needed for the handle  34 .  
         [0051]    The mounting of the handle  34  can be performed through the lateral opening  44  in the sliding shoe  33 . Since a mounting from the front is dispensed with, the central and the rear end of the handle  34  can be designed substantially freely, since they have yet to be introduced through a small opening at the front end of the sliding shoe  33 . This permits, for example, the angling of the plate, from which the handle  34  is produced to form a tab  235  with an opening  135  for passage of the adjusting screw  39 . By expanding the fork during the mounting around the greater radii  38  in the sliding shoe  33 , it is fixedly held in its position by the spring force. A tool for mounting or screwing or the like is not needed.  
         [0052]    [0052]FIG. 11 shows how for producing the belt tensioning required for the operation of the hand-held belt center  10 , the sanding belt  20  is guided over the two rollers  47 ,  48 , in addition to the deviating rollers  31  and the driving roller  46 . The rollers  47 ,  48  operate only for providing the tensioned guidance of the sanding belt  20 .  
         [0053]    As can be seen from FIGS. 12, 13, the clamping/releasing lever  31  is composed of a synthetic plastic material. A multi-bent flat spring  31  is pressed in the synthetic plastic material and has two functions. One end  72  of the spring  71  which is formed as a projection and extends outwardly of the clamping/releasing lever engages in corresponding grooves  73 ,  74  in the housing  12 , so that the lever  51  is arrestable in its both extreme positions. At the other end  75 , the spring  71  carries a V-shaft elongated cortilugation which, after fitting the lever  51  on its rotary axle  82 , engages in slot  77  of the axle  82 . Thereby the lever  51  is secured in an axial direction against displacement. Additional mounting means for fixing the lever  51  on the axial  76  are not necessary. Thereby, the lever  51  can be inserted with flush edge in the housing contour so that it can not be lost but at the same time it is mounted so that it can be easily releasable.  
         [0054]    For mounting the spring  71  in the clamping/releasing lever  51  it carries a further elongated cartugation  78 . The elongated cartugation provides a press fit between the spring  71  and the lever  51  in the mounting groove. The belt clamping rollers  47 ,  48  are composed of synthetic plastic material and run directly slidingly on the steel axles  58 ,  67 .  
         [0055]    In order to prevent deposits of wear particles, sanding dust, etc. on the outer surface of the rollers, the rollers  47 ,  48  are not formed as smooth cylinders, but instead are provided with transverse groups  79 , similarly to a toothed belt sprocket. The dust and wear particles can laterally move out through the transverse grooves. The remaining supporting surfaces of the rollers are to the contrary so small that the dust and the wear particles can not deposit there.  
         [0056]    This makes possible clamping of the grinding band  20  on the hand-held belt sander  10  by two movable clamping rollers  47 ,  48 , which together are actuated by the single clamping/releasing lever  51 . The driving of the second varrying lever  53  is performed through the spring wire  55  while the pressing force of the second bearing lever  52  is provided through an additional torsion spring  59 . The mechanism is connected through the U-shaped blocking spring  71  which blocks it in a clamped position. This blocking is removed by the plug  69  in the clamping/releasing lever  51  during its actuation. For this purpose, a definite slack is provided between the clamping/releasing lever and the bearing lever  52 . A shaped flat spring  71  is pressed in the clamping lever and held through a cartigulation  78  in the clamping/releasing lever  51 . A further cartigulation  75  arrests in the slot  77  the axle  76  of the clamping/releasing lever  51  and thereby secures its axial position. The spring  71  is provided on its free end with a projection  72 . In the extreme positions of the clamping/releasing lever  51  it is arrested in the corresponding grooves  73 ,  74  of the housing  12  and thereby arrests the lever  51 .  
         [0057]    With the use of two clamping rollers  47 ,  48 , instead of an adjustment of the deviating rollers  31  on the tip  333  of the sliding shoe  33  or the hand-held belt sander  10 , constant belt running conditions at the tip can be provided. The reason is that it always remains in the same position and thereby the belt  20 , independently from the belt tensioning runs always identically on the pressing surfaces  88 ,  89  or bases  133 ,  233  of the sliding shoe  33 .  
         [0058]    FIGS.  5 - 8  and  10  show how the total support of the belt clamping mechanism for the hand-held belt sander  10  is provided by the transmission cover  57 . For this purpose two pins  77 ,  82  are riveted on the transmission cover  57  which is formed as a punched member. They operate as axles for both bearing levers  52 ,  53 . Furthermore, the transmission cover  57  is connected through circular-arc-shaped punched portions  83 ,  84  operating for guiding and limiting the rotary movement of the bearing levers  52 ,  53 . Also, it is mounted through a formation  63  under the clamping spring  59  of the clamping mechanism. Thereby the total clamping mechanism is premounted on the transmission cover  57 .  
         [0059]    For fixing the transmission cover  57  in the housing  12 , it is provided with openings  85 , so that housing plugs  90  engage in them during the mounting. During the mounting the transmission cover  57  is clamped between the sliding shoe  33  and the housing  12  and fixed in connection with the known positioning plugs  90 . Therefore, no further mounting elements are needed.  
         [0060]    The transmission cover  57 , in addition to the receipt of the clamping mechanism, also performs other functions. A collar  86  produced by punching receives the needle bearing  87  for the drive shaft  91 . The collar  86  serves simultaneously as a centering for a buffer disk of ceramic. It prevents a damage of the housing during a lateral running of the sanding belt  20  on the transmission cover  57  in the region of the driving roller  46 . A further formation  88  prevents a turning of the buffer disk  92  which is flatened radially at one side. This flatening engages exactly into the above mentioned formation  88 .  
         [0061]    The axial securing of the buffer disk  92  performs during mounting by the sliding shoe  33  which for this purpose is provided with a special claw  89  which extends over the buffer disk  92 . The sliding shoe  93  is centered by the dome  90  in the housing  12  and supported through the transmission cover  57  on the housing  12 .  
         [0062]    The cross-sections of the second example of the driving roller  36  shown in FIGS. 14 a - 14   b  have a specially defined peripheral region. With the use of a softer rubber mixture for the casing of the driving roller, a higher friction value is provided. With 2K tips a hard material is combined with soft strips to counteract the disadvantage that the rubber at high temperatures is soft, it deforms and wears out.  
         [0063]    The driving roller  46  can sprinkled with a not shown grain material for example by glueing standard sanding agents. With this construction the friction value is also increased.  
         [0064]    The arrangement of not shown wire brushes on a surface of the rollers composed of porous material also increases the friction value. Tearing-off of the brushes can be counteracted when the brushes are embedded in the material of the rollers so that only a short part extends outwardly the roller.  
         [0065]    The casing of the driving roller  46  can be provided with inclined slots  246  to provide strip-like construction of the soft roller surface with strips  145 . Thereby an increase surface pressure under load onto the sanding belt  20  is obtained, since the strips which are inclined in the running direction of the sanding belt  20  is obtained, since the strips which are inclined in the running direction of the sanding belt  20  are arranged under the driving force of the belt. The roller diameter of the driving roller  46  is increased and the belt tensioning is increased as well, which leads to higher transmittable force to the sanding belt  20 . Furthermore, when the flattening is provided, a so-called polygon effect is achieved. The reason is that the sanding belt  20  with raised projection of the strips  146  no longer uniformly abuts against the whole surface of the roller, but instead runs only on the edges of the strips. As a result, a substantially higher surface pressure is provided.  
         [0066]    In accordance with FIGS. 15 a ,  15   b ,  15   c , similarly to a free running drive, the driving roller  46  is knotched so that six arresting elements can be pressed in the knotches  2146  connected by an undercut and produced for example by extrusion. The arresting members can be formed of metal or synthetic plastic material which raise underload. This arresting members in contrast to projections, are not deformable, so that the desired affect of the pressing force increase is provided here in stronger way.  
         [0067]    In accordance with a not shown embodiment of the invention, the roller can be provided with a coating composed of brushes. Similarly to the fleece, the ruffle up during stroking against the nap.  
         [0068]    In accordance with a further not shown embodiment of the invention, an additional pressing roller is provided. It presses the belt radially outwardly against the driving roller  46  so that the transmittable force or the embracing angle can be increased. If the pressing roller is composed of a sufficiently soft material, practically no wear occurs, as long as it runs on the sanding side of the belt.  
         [0069]    In accordance with still further not shown embodiment of the invention, the sanding belt is perforated, substantially as in a small film. The perforations can be arranged on the belt not only at the edge, but also in the center or at any other place. Radially outwardly extending pins of the driving roller engage in the perforations so as to provide a form-locking connection and therefore an optimal force transmission.  
         [0070]    Finally, in accordance with still another embodiment of the invention, a profiled is applied to the inner side of the belt. For example, transverse grooves corresponding to a toothed belt can be provided, while the driving roller has a corresponding counter profile, so that also a form-locking connection between the sanding belt and the driving roller is produced.  
         [0071]    It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.  
         [0072]    While the invention has been illustrated and described as embodied in hand-held belt sander, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.  
         [0073]    Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.