Abstract:
A pneumatically operated, random orbital sander is disclosed as having an upper seal adapted to retard the entry of dust into an exposed or lowermost motor shaft supporting bearing and a lower seal adapted to retard the entry of dust into a motor shaft mounted bearing serving to couple the motor shaft to a sanding pad or disc.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Random orbital sanders are well known and typically comprise a pneumatically operated motor having a casing suitably mounted within a manually manipulated housing and a balanced, motor shaft supported for rotation relative to the motor casing by uppermost and lowermost bearings; and a motor shaft mounted bearing serving to couple the motor shaft to a sanding pad or disc.  
           [0002]    Prior sanders of the type generally described are known to be subject to bearing failure resulting from the egress of dust particles thereinto during use. In this respect, a lowermost motor shaft support bearing is particularly subject to failure resulting from its direct exposure to a dusty or sanding environment during use and the tendency for dust ladened air to be momentarily drawn upwardly therethrough towards the interior of the motor each time the motor is turned off. The uppermost motor support bearing is known to have a substantially longer useful operating life in that it is normally shielded from dust, due to its placement wholly within the confines of the housing of the sander.  
           [0003]    There is no known means adopted for use in sealing the lowermost motor shaft supporting bearing against the ingress of dust particles, and thus resultant failure of such bearing can severely reduce the useful operating life of a random orbital sander, particularly when used in an environment where highly abrasive dust particles are generated.  
           [0004]    The motor shaft mounted bearing employed to couple the drive shaft to a sanding pad or disc is also know to be subject to failure due to the ingress of abrasive dust particles, and in commonly assigned U.S. Pat. No. 4,854,085 there is described a dust seal having utility with this type of bearing. However, this dust seal has the disadvantage of being of multiple part construction.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention relates to seals particularly adapted to seal bearings of random orbital sanders against the egress of dust particles, such as would otherwise shorten the useful life of such sanders.  
           [0006]    There is disclosed two unique types of dust seals wherein a first of such seals is particularly adapted to create a seal against the ingress of dust into a lowermost bearing serving to mount a motor shaft for rotation relative to a motor casing, and a second of such seals is particularly adapted to create a seal against the ingress of dust into a motor shaft mounted bearing serving to couple the motor shaft to a sanding pad or disc to be driven thereby.  
           [0007]    In the first seal there is provided a deformable felt washer, which is adapted to bridge between and sealing engagement with the motor shaft and a lower end or bearing supporting plate of the motor casing, and a cap adapted to be clamped against the bearing supporting plate incident to mounting of the motor casing within the sander housing, whereupon the cap serves to clamp an outer peripheral surface of the washer in sealing engagement with the supporting plate. The washer has its central or through opening sized to provide a rotary sliding seal with a cylindrical, radially outwardly facing surface of the motor shaft and is preferably adapted to have an inner peripheral surface placed in sealing engagement with an axially facing, radially and annularly extending surface of the motor shaft incident to assembly of the motor shaft with the motor casing. The washer is preferably air permeable to allow flow of pressurized air escaping from the motor across the lowermost bearing for cooling purposes.  
           [0008]    In the second seal, there is provided a resiliently deformable sealing ring having a radially outwardly facing peripheral edge surface adapted to be positioned in sealing engagement with a radially inwardly facing surface of the motor shaft; an adjacently dispersed axially facing surface adopted to be positioned in sealing engagement with an outer race of the motor shaft supported bearing; a first resiliently deformable annular lip arranged to project radially inwardly of the sealing ring for rotary sliding engagement with a radially outwardly facing cylindrical surface of a balancer bearing shaft forming part of the coupling for the sanding pad or disc, and a second resiliently deformable, annular lip arranged to project axially of the sealing ring for rotary sliding engagement with an axially facing, radially extending surface of the balancer bearing shaft. 
       
    
    
     DRAWINGS  
       [0009]    [0009]FIG. 1 is a prospective view of a manually manipulated, pneumatically operated sander incorporating the present invention with portions of its housing broken away;  
         [0010]    [0010]FIG. 2 is an enlarged side elevational view of the motor and balancer assemblies with the assembly mounting or lock ring removed;  
         [0011]    [0011]FIG. 3 is an enlarged sectional view taken generally along the line  3 - 3  in FIG. 2 with the mounting ring shown in unclamping position;  
         [0012]    [0012]FIG. 4 is fragmentary view showing the mounting ring in clamping position;  
         [0013]    [0013]FIG. 5 is an exploded, prospective view showing elements of the balancer assembly;  
         [0014]    [0014]FIG. 6 is a view of the upper bearing seal dust cap shown in section;  
         [0015]    [0015]FIG. 7 is a top plan view of the upper bearing seal dust cap;  
         [0016]    [0016]FIG. 8 is a top plan view of the upper bearing seal washer;  
         [0017]    [0017]FIG. 9 is a side elevational view of the upper bearing seal washer;  
         [0018]    [0018]FIG. 10 is an enlarged view of the lower bearing flexible ring seal shown in section; and  
         [0019]    [0019]FIG. 11 is a top plan view of the lower bearing ring seal. 
     
    
     DETAILED DESCRIPTION  
       [0020]    Reference is first made to FIG. 1, wherein a random orbital sander is designated as  10  and shown as generally including a manually manipulated housing  12  defining a downwardly opening chamber  14  sized to receive a motor  16  retained within the chamber by a lock or mounting ring  18  threadably fixed to the housing and including a balanced motor driven shaft  20 ; and a coupling  22  for mounting a sanding pad or disc  24  for orbital movement relating to the motor shaft.  
         [0021]    Motor  16  is shown in FIGS.  1 - 3  as generally comprising a casing defined by upper and lower end or bearing support plates  26  and  28  having upwardly and downwardly facing recesses  26   a  and  28   a  for mounting uppermost and lowermost bearings  30  and  32  serving to support motor shaft  20  for rotation about a first axis  20   a , and an annular side wall  36  cooperating with the end plates to bound a motor chamber  38  receiving a plurality of rotor blades  40  for rotation with the motor shaft. Recess  28   a  is radially bounded by a cylindrical side wall  28   b  having an outwardly facing cylindrical side wall surface  28   c  and an axially facing, annular end wall surface  28   d . End plate  28  is also provided with an axially facing annular surface  28   e  extending outwardly of side wall surface  28   c.    
         [0022]    Bearings  30  and  32  are formed, respectively, with inner and outer races  30   a ,  32   a  and  30   b ,  32   b ; and a plurality of ball or roller elements  30   c ,  32   c . Chamber  38  is arranged for flow communication with a suitable source of fluid, such as air, under pressure via a valve controlled housing inlet passage  42  and a chamber inlet  44  and with a housing discharge passage  46  via a chamber discharge openings, not shown.  
         [0023]    Motor shaft  20  is suitably fixed for rotation with inner races  30   a  and  32   a , and maintained in assembled condition relative to end plates  26  and  28  and side wall  36  by snap ring retainer  50 .  
         [0024]    Motor shaft  20  is best shown in FIGS. 3 and 5 as having an enlarged lower end  52 , which includes a shaft balancing weight  54  and defines a downwardly opening cylindrical cavity or chamber  56 . Cavity  56  is shown in FIG. 3 as being stepped to define an inner cylindrical recess surface  56   a  and a radially enlarged outer cylindrical recess surface  56   b  having an annular recess  58  for receiving a snap ring retainer  58   a.    
         [0025]    Coupling  22  is best shown in FIG. 3 as including a bearing  60  formed with inner and outer races  60   a  and  60   b , and ball or roller elements  60   c , and a balancer bearing shaft  62 , which is supported by inner bearing race  60   a  for rotation about a second axis  62   a  disposed parallel to motor shaft axis  20   a.    
         [0026]    Bearing outer race  60   b  is sized to be slide fitted within cavity recess surface  56   a  and preferably retained therein by a suitable adhesive, such as Loctite. Balancer bearing shaft  62  is preferably press fit within the inner race  60   a , and, if desired, bonded thereto by a suitable adhesive, such as Loctite. Sanding pad  24  may be suitably, removably fixed to balancer bearing shaft  62 , such as by a fastener, not shown, threadably received within shaft opening  64  aligned with axis  62   a.    
         [0027]    Balancer shaft  62  is shown as having an outwardly facing cylindrical surface  62   b  and axially facing annular surface  62   c  defined by an enlarged head portion  62   d.    
         [0028]    As thus far described, sander is of known construction and generally disclosed, as by way of example, by commonly assigned U.S. Pat. Nos. 4,854,085 and 5,538,086.  
         [0029]    In accordance with the present invention, an otherwise conventional orbital sander is provided with a first seal  70  intended to block ingress of dust particles into lowermost motor shaft support bearing  32 , and a second seal  72  intended to prevent the ingress of dust particles into motor shaft mounted bearing  60 .  
         [0030]    Seal  70  is shown in FIGS.  3 - 9  as being of two part construction including a deformable washer  74  preferably formed of a 100% polyester felt material, and a cap  76  preferably formed of Nylon. Washer  74  is preferably air permeable, so as to allow the flow of pressurized air escaping from motor chamber  38  across bearing  32  for cooling purposes.  
         [0031]    Washer  74  is sized such that its outer diameter is sufficient to provide an annular, axially facing sealing surface  78  adapted to engage with end wall surface  28   d  of lower end plate  28  radially outwardly of bearing recess  28   a  and its inner diameter is such that there is provided a radially inwardly facing edge surface  82  disposed for rotary sliding engagement with a radially outwardly facing cylindrical surface  84  of the motor shaft. In its as formed state, washer  74  has a flat rim portion with its oppositely facing annular sealing and clamping surfaces  78  and  86 , respectively, essentially parallel to one another. In this construction, end wall surface  28   d  becomes a sealing surface and end plate annular surface  28   e  becomes a clamping surface.  
         [0032]    In the illustrated construction, an axially facing surface  52   a  of motor shaft lower end  52 , which extends radially of cylindrical surface  84 , extends annularly of axis  20   a  through less than 360°, due to space limitations determined by the available distance between axis  20   a  and second axis  62   a . However, if space allows, it is preferable to extend surface  52   a  through 360° in order to provide a further annular seal between surface  52   a  and washer clamping surface  86 .  
         [0033]    Cap  76  is best shown in FIGS.  3 - 7  and including radially extending annular flange portion  88 , a cylindrical portion  90  arranged to depend from the radially inner edge of portion  88 , and an annular flange portion  92  arranged to project radially inwardly from the lower edge of portion  90 . Flange portion  88  has oppositely facing and essentially parallel first and second annular cap clamping surfaces  88   a  and  88   b  sized to extend radially outwardly of end plate side wall surface  28   c  for engagement with axially facing outer annular clamping surface  28   e  of end plate  28  and an o-ring  94  carried by lock ring  18 . Cylindrical portion  90  has a radially inwardly facing surface  90   a  sized to be slidably supported by end plate side wall surface  28   c . Cap flange portion  92  provides a third clamping surface  92   a.    
         [0034]    It will be understood by referring to FIGS. 1 and 3 that upon threadably connecting lock ring  18  to housing  12  for purposes of mounting motor, o-ring  94  is adapted to be brought into clamping engagement with second cap clamping surface  88   b  for purposes of clamping first cap clamping surface  88   a  against end plate clamping surface  28   e  with the result that third cap clamping surface is drawn upwardly into clamping engagement with washer clamping surface  86  and washer scaling surface  78  forced into scaling engagement with end plate end wall surface  28   d . In the arrangement shown in the drawings the lower end  32   b  of outer race  32   b  projects slightly outwardly of recess  28   a  beyond end plate end wall surface  28   d  with the result that washer  74  is deformed, as shown in FIGS. 3 and 4, as lock ring  18  is threaded into housing  12 , and surface  78  is also placed in tight sealing engagement with outer bearing lower end  32   b . With this construction, washer  74  serves to bridge between end plate  28  and motor shaft  20  and create a dust seal tending to prevent the ingress of dust particles to lower bearing  32 .  
         [0035]    During operation of sander  10 , pressurized air tends to escape from motor chamber  38  through the annular path defined by lower end plate  28  and motor shaft  20 , and due to the air permeable nature of washer  74 , is permitted to flow axially of bearing  32  in order to cool such bearing. Washer  74 , also permits the reverse flow of air across bearing  32  each time motor  16  is turned off, but prevents passage of dust into the bearings which would otherwise occur in the absence of such washer.  
         [0036]    Second seal  72  is preferably in the form of a resiliently deformable ring fabricated of a high temperature, chemical and abrasion resistant material, such as 70 duro-carboxyladed nitrile material with balancer bearing shaft surfaces  62   b  and  62   c  serving to define cooperating sealing surfaces.  
         [0037]    The sealing ring is defined by a radially extending annular flange  96 , a radially inwardly projecting flexible annular first sealing lip  98  and an axially projecting flexible annular second sealing lip  100 . As best shown in FIG. 3 the elements of the sealing ring are sized such that first seal lip  98  is resiliently deformed for rotary sealing engagement with balancer shaft surface  62   b  and second sealing lip is deformed for rotary sealing engagement with balancer shaft surface  62   c  incident to placement of the balancer shaft within bearing  60 . Also, it will be understood that the thickness and diameter of flange  96  is such that installation of retainer  58   a  serves to clamp flange portion  96  in sealing engagement with a lower annular surface  60   d  of outer bearing race  60   b  and preferably also to resiliently deform the flange portion sufficiently to force its radially outwardly facing edge surface  102  into sealing engagement with recess surface  56   b  intermediate outer race  60   b  and retainer  58   a.    
         [0038]    With this construction, the sealing ring bridges between balancer bearing shaft  62  and motor shaft  20  and serves to create a dust seal tending to prevent ingress of dust particles into further bearing  60 .