Abstract:
A belt sander ( 2 ) comprising a housing ( 4 ) and having a lower sanding surface ( 40 ) and an upper sanding surface ( 42 ) opposite the first sanding is disclosed. The sander has a larger rear roller ( 32 ) driven by a motor ( 22 ), a front roller ( 34 ) of smaller diameter than the rear roller, and an endless sanding belt ( 38 ). A guard ( 48 ) is pivotable between a lowered position preventing access to the upper sanding surface and a raised position allowing access to the upper sanding surface. A handle ( 12 ) on the housing is pivotable between a first handle position adjacent the upper sanding surface and at least one second handle position further from the upper sanding surface than the first handle position.

Description:
FIELD OF THE INVENTION 
   The present invention relates to sanding apparatus, and relates particularly, but not exclusively, to belt sanders for sanding wooden floors. 
   BACKGROUND OF THE INVENTION 
   Belt sanders are known in which an endless abrasive sanding belt passes around a driving roller and a driven roller, and the driving roller is rotated by means of a toothed belt driven by a motor to cause the sanding belt to move over a generally flat base surface located between the driving and driven rollers. 
   U.S. Pat. No. 6,174,226 discloses a handheld belt sander which has opposed first and second sanding surfaces. 
   JP 2000-280157 discloses a belt sander which provides a pivotable cover which selectively prevents access to an upper sanding surface of the sander. However, this arrangement suffers from the disadvantage that the accuracy with which sanding can be carried out is limited, for a given size of sander. 
   Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art. 
   BRIEF SUMMARY OF THE INVENTION 
   According to the present invention, there is provided a sanding apparatus comprising: 
   a housing defining a first base surface and a second base surface opposite said first base surface; 
   at least one first roller and at least one second roller, wherein at least one said first roller has a diameter larger than a diameter of at least one said second roller; 
   a motor for driving at least one said first roller for causing an endless abrasive belt passing around at least one said first roller and at least one said second roller in use to move across said first and second base surfaces to define first and second sanding surfaces respectively; 
   at least one guard member moveable between a first guard position preventing access to said second sanding surface and at least one second guard position allowing access to said second sanding surface; and 
   at least one handle on said housing, wherein at least one said handle is moveable between a first handle position adjacent said second sanding surface and at least one second handle position further from said second sanding surface than said first handle position. 
   By providing a sander having at least one first roller and at least one second roller of smaller diameter than the first roller, this provides the advantage of enabling accurate sanding operations to be carried out for a given size of sander, while the provision of a movable guard member provides a further sanding surface which may be selectively accessible. 
   At least one said guard member may be pivotable between said first and second guard positions thereof. 
   At least one said handle may be pivotable relative to said housing between first and second handle positions thereof. 
   The apparatus may further comprise locking means for preventing movement of at least one said handle from a second handle position thereof to said first handle position when at least one said guard member is in a said second guard position thereof, and/or for preventing movement of at least one said guard member to a second guard position thereof when at least one said handle is in a first handle position thereof. 
   The locking means may comprise linkage means interconnecting at least one said handle and at least one said guard member such that movement of at least one said handle to the first handle position thereof causes movement of at least one said guard member to the first guard position thereof. 
   The locking means may comprise at least one linkage member adapted to engage a respective handle to prevent movement of said handle relative to the housing to said first handle position when a predetermined said guard member is in the second guard position thereof. 
   At least one said linkage member may comprise a respective protrusion and/or slot adapted to engage a corresponding slot and/or protrusion on a respective said handle. 
   The locking means may comprise at least one linkage member adapted to engage at least one guard member to prevent movement of said guard member to said second guard position thereof when a said handle is in said first handle position thereof. 
   At least one said linkage member may comprise a respective recess and/or protrusion for engaging a corresponding protrusion and/or recess on at least one said guard member. 
   At least one said linkage member may be pivotable relative to the housing between a first position allowing movement of at least one said guard member to a second guard position thereof and a second position preventing movement of said guard member to said second guard position, wherein movement of said linkage member to said first position is prevented when said handle is in a first handle position thereof. 
   A plane defined by said first base surface may be substantially tangential to a predetermined said second roller. 
   By arranging a predetermined said second roller to be substantially tangential to a plane defined by the first base surface, this provides the advantage that the limit of the region sanded by the sanding apparatus is now defined by the bottom of the predetermined second, as opposed to the edge of the base surface, as a result of which the region which cannot be sanded by the present invention is as wide as the radius of the predetermined second roller, whereas this region in the prior art is at least as wide as the whole diameter of one of the rollers. As a result, the present invention has the advantage that sanding much closer to the edge of a floor can be carried out. 
   The spacing of said predetermined second roller from said first base surface may be adjustable. 
   This provides the advantage of enabling the tension in the belt to be adjusted. 
   The predetermined second roller and a base portion defining said first base surface may include cooperating engaging means for enabling said predetermined second roller to slide relative to said first base surface. 
   This provides the advantage of providing a simple means of adjusting the spacing between the predetermined second roller and the first base surface, while maintaining the predetermined second roller tangential to the plane defined by the first base surface. 
   The predetermined second roller may be displaceable towards said first base surface to facilitate mounting and/or removal of said endless belt. 
   A first said roller located furthest from the or each said second roller may be substantially tangential to said second base surface but not to said first base surface. 
   The apparatus may further comprise a third base surface substantially coplanar with said first base surface, and an inlet between said first and third base surfaces for enabling the endless belt to pass through said inlet and around said first roller located furthest from the or each said second roller. 
   In a preferred embodiment, the motor is located in use on a side of the endless belt remote from said first base surface and an output shaft of said motor is substantially parallel to an axis of rotation of a first said roller adapted to be driven by said motor. 
   By providing the motor on a side of the endless belt remote from the first base surface and an output shaft of said motor substantially parallel to an axis of rotation of a first said roller adapted to be driven by said motor, this provides the advantage of enabling the apparatus to be constructed more compactly. For example, by passing a toothed belt around gears connected to the ends of the motor output shaft and the first roller axis, the motor does not need to be laterally offset relative to the sanding belt, as a result of which the width of the apparatus is only slightly larger than that of the sanding belt. 
   The apparatus may further comprise a drive belt connected between an output shaft of said motor and a said first roller. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which: 
       FIG. 1  is a perspective view of a sander embodying the present invention from the front and a first side with a guard in a lowered position; 
       FIG. 2  is an elevation view of the sander of  FIG. 1  from the first side; 
       FIG. 3  is a top view of the sander of  FIG. 1 ; 
       FIG. 4  is a bottom view of the sander of  FIG. 1 ; 
       FIG. 5  is a rear view of the sander of  FIG. 1 ; 
       FIG. 6  is a front view of the sander of  FIG. 1 ; 
       FIG. 7  is a perspective view from the front and a second side of the sander of  FIG. 1 ; 
       FIG. 8  is an elevation view from the second side of the sander of  FIG. 1 ; 
       FIG. 9  is a cross sectional elevation view of the sander of  FIG. 1  from a first side; 
       FIG. 10  is a cross sectional elevation view of the sander of  FIG. 1  from a second side; 
       FIG. 11  is a view, corresponding to  FIG. 1 , of the sander with the guard and handle thereof in a raised position; 
       FIG. 12  is a perspective view of a handle, guard and locking mechanism of the sander of  FIG. 1 , with the guard and handle in a lower position; 
       FIG. 13  is a view, corresponding to  FIG. 12 , with the handle in a raised position; 
       FIG. 14  is a view, corresponding to  FIG. 12 , with the handle and guard in raised positions; 
       FIG. 15  is a front view of the handle, guard and locking mechanism of  FIG. 12 ; 
       FIG. 16  is a top view of the handle, guard and locking mechanism of  FIG. 12 ; and 
       FIG. 17  is a rear view of the handle, guard and locking mechanism of  FIG. 14 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A belt sander  2  has a housing  4  of durable plastics material and having a generally wedge shaped base portion  5  defining a generally flat base surface  6  and a rear handle  8  having a trigger  10 . Flat base surface  6  may comprise a separate metal plate attached to base portion  5 . A power cable (not shown) extends from the handle  8  for supplying electrical power to the sander  2 . A forward handle  12  is pivotable about pivot axis  14  relative to the housing  4  and is lockable in selected angular positions relative to the housing by means of a locking lever  16  which is pivoted outwardly of the housing  4  in the direction of arrow A ( FIG. 1 ) to release the handle  12  and is pivoted inwardly to lock the handle  12 . Pivot axis  14  extends substantially transversely to a vertical plane containing the major axis of sander  2  and base portion  5 . (The major axis extends horizontally (left to right) on the page of  FIG. 2  and the vertical plane containing the axis extends perpendicularly to the page in  FIG. 3 .) In particular, the handle  12  is provided with suitable engaging means, which will be familiar to persons skilled in the art, which locate the handle  12  at selected angular positions about pivot axis  14 . The lever  16  can operate in a number of possible ways, for example by means of cooperating cam surfaces. This enables the user to choose the most ergonomic position of the handle  12  for the particular task. 
   The housing  4  also defines a duct  18  ( FIG. 9 ) connecting an inlet  20  in the base  5  of the housing with a motor  22  having an output shaft  24  which also carries a fan (not shown). The fan displaces air radially outwardly through an outlet  28  into a dust bag (not shown). The fan is surrounded by a closely fitting flange to divide the space occupied by the fan into a clean air chamber axially separated from a dirty air chamber. Air drawn into the clean air chamber through air inlets  26  in one or both sides of the housing  4  cools the motor, while air is drawn into the dirty air chamber through inlet  20  via duct  18 , and all of the air drawn into the fan is expelled through outlet  28 . As a result, dust produced by the sanding operation is drawn through inlet  20  and expelled into the dust bag, in a manner described in greater detail below. 
   Housing  4  includes cylindrical motor receiving chamber  41  disposed at a location between the locations of front roller  34  and rear roller  32  taken along a major axis of sander  2 . Chamber  41  is disposed at a higher vertical position than both rollers  32  and  34 . Motor  22  is received within chamber  41 . The output shaft  24  of the motor  22  is rotatable about axis  24   a  which is substantially transverse to the major axis and carries a gear  25  for driving a toothed belt  30  ( FIG. 10 ) which passes around a gear  33  mounted to a rear roller  32  arranged in a lower part of the housing  4  above inlet  20 . The gear  33  is rotatable about axis  32   a  and has larger diameter than the gear  25 , which enables the rotational speed of the rear roller  32  to be chosen. The axes  24   a  and  32   a  are generally parallel to each other, which enables the motor  22  to be located above the base portion  5  and laterally in line therewith, which in turn enables compact construction of the sander. A front roller  34 , having smaller diameter than the rear roller  32 , is arranged in the lower part of the housing such that a lowermost point  36  of the front roller is in line with the base surface  6 . The front roller  34  is of concave cross-section to assist in retaining in position an endless sanding belt  38  ( FIG. 9 ) which passes around the front  34  and rear  32  rollers and across the base surface  6  to define a lower sanding surface  40  and an upper sanding surface  42 . Front roller  34 , rear roller  32  and base  5  jointly define a path for receiving belt  38  of standard size, that is, having a width of seventy five mm (usually expressed as three inches) transverse to the major axis and having a perimeter of either eighteen or twenty one inches. The rear roller  32  is generally tangential to an upper surface  7  of wedge shaped base portion  5 , but is offset relative to the flat base surface  6 , as a result of which the direction of belt  38  changes as it passes around rear edge  6   a  of base surface  6 , so that the belt  38  is asymmetrically arranged relative to a line joining the central axes of front and rear rollers  34 ,  32 . Housing  4  includes an undersurface  43  which extends at a forwardly downwardly inclined angle from a location above rear roller  32  towards front roller  34 . The overall inclination angle of undersurface  43  may be ten degrees relative to the horizontal. 
   With reference to  FIGS. 1 and 2 , the gripping surface of handle  12  is curved and is located generally within a plane which extends in a direction transverse to the major axis of sander  2 . Handle  12  is secured to an upper portion of motor receiving chamber  41 , at a location between the locations of front roller  34  and rear roller  32  taken along a major axis of sander  2 . Like chamber  41 , handle  12  is disposed at a higher vertical position than both rollers  32  and  34 . 
   The front roller  34  is slidably mounted to the front of the base part  5  of the housing  4  by means of a support  44 , and the support  44  is urged forwardly by a compression spring (not shown) to maintain the tension in the sanding belt  38 . A lever  46  on the base part  5  of the housing can be pivoted outwards in the direction of arrow B shown in  FIG. 1  to place the spring under compression by means of a cam surface to enable the support  44  to be moved inwardly to remove the sanding belt  38  for replacement or for adjustment. The front roller  34  is also provided with an adjustment knob  35  for adjusting the angle of the longitudinal axis of the roller  34  relative to the housing  34 . 
   The upper sanding surface  42  is covered by a guard  48  which is pivotable relative to the housing about an axis  50  between a lower position and an upper position. In the lower position the guard  48  covers the upper sanding surface  42  and prevents access to it and a front portion  52  of the guard extends forwardly of forwardmost part  54  of the sanding belt  38 . In the upper position of the guard  48 , access to the upper sanding surface  42  is permitted, for example for sanding the underside of objects such as tables, or for sanding non-level surfaces such as door frames. 
   A rear part  56  of the guard  48  has a cam  58  ( FIG. 13 ) having a cam surface  60  on a side thereof which cooperates with a side surface of an end  62  of a linkage member  64  mounted to a pivot  66 . As a result, movement of the guard  48  from its lower to its upper position causes the cam surface  60  to displace end  62  of the linkage member  64  to the left in  FIG. 13 , which then urges the linkage member  64  in a clockwise direction about the pivot  66  in the direction of arrow C in  FIG. 13 . The linkage member  64  is received in a slot  68  in the handle  12  when the guard  48  is in its upper position and when the handle  12  is pivoted upwardly relative to the housing  4  as shown in  FIG. 13  to allow the guard  48  to pivot to its raised position. However, the linkage member  64  is prevented from pivoting in the direction of arrow C when its upper end  70  is not aligned with slot  68 , which in turn prevents the guard  48  from being raised when the handle  12  is in its lowered position as shown in  FIG. 12 . Similarly, location of upper part  70  of linkage member in slot  68  when the guard  48  is in its raised position prevents rotation of the handle  12  relative to the housing  4 , as a result of which the handle  12  can not be pivoted to its lowered position when the guard  48  is raised. This minimises the risk of injury to a user&#39;s hand through inadvertent contact with the upper sanding surface  42  when the handle  12  is in its lowered position as shown in  FIG. 9 . Suitable means (not shown) may be provided to retain the guard  48  in its raised or lowered position when the handle  12  is in its raised position to keep the guard  48  stationary during use. 
   The operation of the sander  2  will now be described. 
   In normal use of the sander  2 , i.e. in which sanding is carried out by means of the lower sanding surface  40 , the guard  48  covers the upper sanding surface  42 , and the handle  12  is locked in any one of its permitted angular positions about axis  14  relative to the housing by means of the locking lever  16 . The user actuates the motor by pressing trigger  10  on handle  8 , as a result of which the motor  22  drives rear roller  32  to cause movement of the sanding belt  38  around front  34  and rear  32  rollers and upper  40  and lower  42  sanding surfaces in the direction of arrow D shown in  FIG. 9 . At the same time, rotation of the fan creates an air current entering inlet  20 . This causes air containing dust produced by the belt  38  at lower sanding surface  40  to be drawn into inlet  20  as the belt  38  enters inlet  20  to pass around the rear roller  32 , and the dust containing air then passes along duct  18  into the dirty side of the fan and is expelled through outlet  28  into the dust bag (not shown). 
   Because the forwardmost part of the lower sanding surface  40  is defined by the lowermost  36  part of the front roller  34 , only that part of the sander  2  forwardly of the rotation axis of the front roller  34  lies above the forwardmost part of the lower sanding surface  40 . As a result, the sander  2  can be used to sand much closer to the edge of floors than is the case with conventional sanders. In particular, by minimizing the diameter of front roller  34  while still maintaining a transverse width of 75 mm for the belt receiving path and providing for the use of standard size belt loops, the present invention provides the material removal capabilities of a full size belt sander but allows sanding much closer to a vertical wall. To minimize the gap between the sanding border and such a wall, front roller  34  may have a maximum diameter of approximately 23 mm and preferably a diameter of 16.5 mm. This structure allows the sander to sand within 15 mm of the vertical wall. Including base surface  6 , this structure allows the sanding belt to contact the sanded surface for a length of approximately 195 mm along the major axis. Contact between the front part  54  of the sanding belt  38  and a vertical surface such as a wall (not shown) is prevented by the front portion  52  of the guard  48 , which extends forwardly of the front part  54  of the belt  38  by approximately 5 mm when the guard  48  is in its lower position. This prevents inadvertent damage to, for example, skirting boards at the edge of a floor to be sanded. 
   In order to use the upper sanding surface  42 , the locking lever  16  is pivoted outwardly of the housing  4  to enable pivoting of the handle  12  about axis  14 , and the handle  12  is pivoted to its upper position, as a result of which the upper part  70  of linkage member  64  is aligned with slot  68  in the handle  12  to allow the linkage member  64  to pivot about pivot  66 . The guard  48  is then pivoted upwardly by means of a suitable actuator member (not shown), for example a lever located adjacent pivot axis  50  to expose the upper sanding surface  42 . The guard  48  is then retained in its upper position by suitable means. 
   The sander of the present invention also allows for sanding beneath an overhanging edge. The upper surface of base  5  has a forwardly downward inclination. Undersurface  43  has a corresponding downward inclination. This inclination along with the relatively flat upper surface of housing  4  disposed forwardly of motor receiving chamber  41 , and the fact that no portion of the housing extends above this flat upper surface permits the forward end of sander  2  to pass readily beneath an overhanging edge. This structure along with the minimized diameter of front roller  34  allows sanding of a horizontal surface to nearly the edge of such a surface extending beneath the overhanging edge. The flat upper surface may extend approximately 64 mm in the rearward direction from the forward end of housing  4 , and throughout its extent, the flat upper surface is disposed no greater than approximately 36 mm above the lower sanding surface, with no other portion of the housing disposed or extending above the flat upper surface. 
   The diameter of rear roller  32  approximately corresponds to the height of base  5  at the rear edge thereof. The rear roller  32  may have a diameter which is in a range of 2–3 times the diameter of front roller  34 . Preferrably the diameter of rear roller  32  is 48 mm, or approximately 3 times the front roller  34 . In a preferred embodiment, the flat upper surface of housing  4  is formed by the upper surface of guard  48 . 
   When the sanding belt  38  becomes worn, the lever  46  is pivoted outwardly of the housing  4  to compress the compression spring (not shown). This allows support  44  to be moved rearwardly, as a result of which the belt  38  becomes slack and can more easily be removed for replacement. When a replacement belt  38  has been placed around the rollers  32 , 34 , the lever  46  is then pivoted inwardly to cause the spring to urge the forward roller  34  forwards to place the replacement belt  38  under tension. 
   With further reference to  FIG. 2 , housing  4  includes a rear flat upper surface extending rearwardly from motor receiving chamber  41 , preferably for a distance of at least 50 mm. Housing  4  then curves downwardly about rear roller  32 , and handle support portion  45  extends rearwardly therefrom. Rear handle  8  extends rearwardly from motor receiving chamber  41  and terminates at support portion  45 . Therefore, a gripping surface of handle  8  extends above rear roller  32 , providing increased control for belt sander  2 . Trigger  10  is disposed at the underside of the gripping surface of handle  8 . The maximum height of sander  2  at the location of the rear flat upper surface may be 68 mm. 
   It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.