Patent Publication Number: US-2022220752-A1

Title: Offset mounting adapter for concrete surface processing tool

Description:
FIELD OF THE INVENTION 
     The present invention relates to surface processing machines for mounting surface processing tools and, more particularly, to a method and adapter for mounting surface processing tools, rotatable and otherwise, on the arms of motor driven spider arm assemblies of such machines. 
     BACKGROUND OF THE INVENTION 
     It is known that during the installation of concrete floors, the troweling and finishing operation is performed on the wet concrete using either walk-behind or ride-on power trowels. Inasmuch as at least one type of power trowel machine is generally already on site during the installation of concrete floors, the present invention seeks to use the on-site availability of these machines for surface finishing purposes. As used herein, the term “surface finishing” refers to the desired surface texture on a concrete slab after troweling and final setting of the concrete. In addition, generally, concrete contractors do not have specialty surface processing machines on site for surface finishing and typically do not own such machines. Therefore, where specialty surface processing machines are used to surface finish concrete surfaces, concrete contractors have to invest in and own or lease separate, expensive pieces of equipment. As used herein, the terms “surface processing machines” and “surface processing tools” refers to machines and tools used for surface finishing a concrete slab. 
     In one of its forms, the present invention takes advantage of the larger finished area attainable with ride-on power trowel machines by converting these power trowel machines to surface processing machines suitable for tasks other than troweling. Ride-on power trowel machines typically range in size from approximately 6 feet to slightly more than 10 feet in width and produce a troweled area of up to 40 square feet. The largest units weigh more than a ton and can finish about 30,000 square feet per day. Ride on trowels, such as the trowel machine illustrated in  FIG. 1 , can be configured with two or more spider assemblies, each having a plurality of radially oriented, spaced- apart arms and a trowel blade mounted on and below each arm. The blades on adjacent rotors may be overlapping or non-overlapping. A typical four arm spider assembly suitable for use with either a ride-on or walk-behind power trowel is illustrated in  FIG. 2 . The assembly generally includes four radially extending arms emanating from a central hub, which receives a drive shaft. A trowel blade is mounted directly via bolts or indirectly via a mounting bar on and below each of the arms. Concrete troweling machines having spider assemblies for mounting trowel blades, and the manner of attachment of the trowel blades to the spider arms, are discussed in detail in U.S. Pat. No. 7,059,801—Snyder et al, the disclosure of which is incorporated herein by reference. 
     Converting walk-behind or ride-on trowel machines to general purpose surface processing machines involves providing mounting means which allows the rapid, on-site substitution of surface processing tools, such as circular brushes, on the spider arms in place of the trowel blades which were used during the installation of the concrete floor. Such mounting means have the advantage that they can mount surface processing tools, instead of blades, such as scrubbing, brushing, buffing, grinding and polishing tools, on the spider arms using readily available hand tools in a very short period of time without need for heavy or expensive equipment. Exemplary currently available mounting means which can accomplish the rapid mounting of rotatable surface processing tools on troweling machines are disclosed in U.S. Pat. No. 7,815,393-Snyder et al, the disclosure of which is incorporated herein by reference. Rotatable surface finishing tools are mounted to each of the spider arms, frequently using a mounting bar, with their rotational axes in vertical registry with and directly beneath the spider arm, such that as the spider arms rotate about the hub, the rotatable surface processing tools, e g., circular brushes, on each arm are intended to be free to spin about a mounting axis perpendicular to the spider arms and parallel to the axis of rotation of the spider arms. Likewise, non-rotatable finishing tools, e g., grinding stone holders, are conventionally mounted with their longitudinal axis in vertical registry with and directly beneath the spider arm. 
     During troweling operations on wet concrete surfaces, the surface is finished or smoothed in steps, starting with a rough finish and stepwise moving toward a so-called burnished finish. In the initial steps the spider arms and, thus, the attached trowel blades, are pivoted or pitched by the operator just a few degrees to slightly raise the leading edge of the blade off the concrete surface in order to avoid its inadvertent digging in to the concrete surface while the weight of the troweling machine maintains the trailing edge of the blade in contact with the concrete. The angle θ formed between the blade  36  and the concrete, as shown in  FIG. 3 , is referred to as the pitch of the blade. As surface finishing of the wet concrete progresses, the pitch of the blade is increased gradually from slightly above zero pitch to the maximum pitch of the blades, typically about θ=25°-30° in  FIG. 3 , on successive passes to put increasingly greater pressure on the concrete surface. The terms “leading edge” and “trailing edge” refer to the edges of the trowel blade as a function of the direction of rotation of the spider assembly, i.e., clockwise or counter-clockwise. Correspondingly, the terms “leading side” and “trailing side” refer to the sides of each of the arms  32  of the spider assembly as a function of the direction of rotation of the spider assembly, i.e., clockwise or counter-clockwise. 
       FIG. 4A ,  FIG. 4B , and  FIG. 4C  illustrate an end view of a spider arm  32  when the spider assembly is rotating in a clockwise direction. In this and other figures the arcuate arrow indicates the direction of rotation, i.e. clockwise or counterclockwise, of the spider arm and assembly. Spider arms are typically polygonal in cross section, e.g., square, rectangular, hexagonal, octagonal, etc.  FIG. 4B  shows the spider arm  32  in a horizontal or unpivoted position.  FIG. 4A  illustrates a spider arm  32  pivoted into a leading side  32   a  down position while  FIG. 4C  shows a spider arm  32  pivoted into a trailing side  32   b  down position. Without a blade attached to each spider arm  32 , but with a surface processing tool attached directly under the spider arm, the spider arms of many conventional troweling machines tend to pivot, more or less, toward a trailing side  32   b  inclined down position as shown in  FIG. 4C . If one compares the pivoted trailing side  32   b  inclined down position of the spider arm in  FIG. 4C  with the unpivoted position of the spider arm in  FIG. 4B  it will be appreciated that the trailing side  32   b  pivoted down position is the same as the pitched trowel blade trailing edge down position desirable during wet concrete finishing operations using trowel blades. This tendency to pivot to a trailing side down position presents a problem when trowel blades are removed from the spider arms and surface processing tools, such as brushes, grinding stones, grinding pads or other honing or polishing pads are installed on the spider arms. The problem is particularly, but not exclusively, noted when the surface processing tool is a rotating tool and a bearing is mounted between the spider arm and the tool in an effort to allow the tool to freely spin as the spider arm is circularly driven by the trowel assembly motor. This is because a rotating tool bearing is designed to have enough play to allow it to absorb forces encountered during use, such as a brush striking bumps on the floor or impacting with walls, and this play allows the bearing to pivot severely due to the trailing side down pivoting of the spider arm. The result is that the bearing tends to bind and is unable to freely rotate, causing it to wear more rapidly than it would in normal use. At the same time, the attached surface processing tool is unable to freely rotate, is not oriented flat on the concrete surface and is caused, by the spider arm pivoting, to wear unevenly, which shortens the tool&#39;s useful life. Similar uneven wear is noted when the surface processing tool is non-rotatable, such as a grinding stone surface processing tool housed within a grinding stone holder, when the holder is mounted on and directly beneath the spider arms. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a ride-on power trowel. 
         FIG. 2  is a top perspective view of a four spider arm spider assembly mounting four trowel blades and suitable for use with ride-on surface processing machines. 
         FIG. 3  is a sectional view taken along line A-A in  FIG. 2  showing the pitch of a trowel blade during a finishing operation. 
         FIG. 4A  is a side elevation view of the free end of a spider arm in its leading side down position,  FIG. 4B  shows it in its unpivoted position and  FIG. 4C  shows it in its trailing side down position, when the spider assembly is rotated in a clockwise direction. 
         FIG. 5A  and  FIG. 5B  are a top plan view of two embodiments,  FIG. 5A  and  FIG. 5B , of an offset mounting plate of the present invention. 
         FIG. 6  is an exploded perspective view of one manner in which the offset mounting plate mounts to a bearing, for example, of a rotatable surface processing tool. 
         FIG. 7  is a top perspective view of a circular brush assembly mounted below a spider arm using the offset mounting plate of the present invention. 
         FIG. 8  is a top perspective view of a circular brush assembly mounted above a spider arm using the offset mounting plate of the present invention. 
         FIG. 9  is a top plan view of the assembly of  FIG. 7  when the spider assembly is rotating in a clockwise direction. 
         FIG. 10  is a top plan view of the assembly of  FIG. 7  when the spider assembly is rotating in a counterclockwise direction. 
         FIG. 11  is a partial sectional view taken along line B-B in  FIG. 9 . 
         FIG. 12  is a top plan view of a grinding stone holder mounted below a spider arm using the offset mounting plate of the present invention. 
         FIG. 13  is a top plan view of a grinding stone holder mounted above a spider arm using the offset mounting plate of the present invention. 
         FIG. 14  is a perspective view of a grinding stone holder welded to a mounting bar which is, itself, attached to a spider arm. 
         FIG. 15  is a side perspective view of a spider assembly comprising the mounting adapter and surface processing tool of  FIG. 14 . 
         FIG. 16  is a perspective view of a mounting adapter comprising two rigidly attached separate structures for mounting the rotational axis of a circular brush assembly circumferentially behind the trailing side of a spider arm. 
     
    
    
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the present invention to provide a mounting adapter for mounting the rotational or longitudinal axis of a surface processing tool circumferentially behind the trailing side of a spider arm. 
     It is another object of the present invention to provide such a mounting adapter for surface processing tools which allows their use on conventional power trowel machines having spider assembly arms. 
     It is still another object of the present invention to provide such a mounting adapter which, when mounted between a surface processing tool and a spider arm, overcomes the tendency of the spider arms to pivot toward a trailing side down position and allows the tool to function without uneven wear. 
     It is yet another object of the present invention to provide such a mounting adapter which allows advantage to be taken of the presence at a concrete floor construction site of readily available high square footage capacity power trowel machines for surface processing purposes. 
     It is another object of the present invention to provide such a mounting adapter which allows the rapid, on-site substitution of surface processing tools on spider arms in place of the trowel blades used during concrete floor installation. 
     It is still another object of the present invention to provide such a mounting adapter for surface processing tools on spider assemblies which allows rotatable surface processing tools to spin freely about their axes while the spider arms are rotatably driven in order to encourage more uniform wear of the tools and a longer useful life. 
     The foregoing and other objects are achieved in accordance with the present invention by providing a mounting adapter for mounting a surface processing tool having a rotational or longitudinal axis to at least one spider arm of a motor driven rotatable spider assembly of a surface processing apparatus, said spider arm having a top surface and a bottom surface, and a leading side and a trailing side as a function of the direction of rotation of said spider assembly, said mounting adapter comprising: a first element for removably attaching said adapter to said spider arm and, a second element unitary with or connected to said first element and positioned circumferentially offset behind said first element, said second element comprising means for positioning the rotational axis of rotating surface processing tools or the longitudinal axis of non-rotatable surface processing tools circumferentially offset behind said trailing side of said spider arm. 
     In accordance with another aspect of the invention, the present invention provides a method for mounting a surface processing tool having a rotational or longitudinal axis to at least one spider arm of a motor driven rotatable spider assembly of a surface processing apparatus, said spider arm having a top surface and a bottom surface, and a leading side and a trailing side as a function of the direction of rotation of said spider assembly, said method comprising:
     removably attaching a mounting adapter to said spider arm, said mounting adapter comprising a first element for attachment to said spider arm and a second element unitary with or connected to said first element and positioned circumferentially offset behind said first element; and   attaching said surface processing tool to means on said second element for positioning the rotational axis of rotating surface processing tools or the longitudinal axis of non-rotatable surface processing tools circumferentially offset behind said trailing side of said spider arm.   

     In accordance with still another aspect of the invention, said first element comprises an elongate handle and said second element comprises a planar plate, wider than said handle, and extending generally perpendicularly from said handle between one end of said handle and a point intermediate the ends of said handle, said planar plate comprising means for positioning the rotational axis of rotating surface processing tools or the longitudinal axis of non-rotatable surface processing tools circumferentially offset behind said trailing side of said spider arm. 
     In accordance with yet another aspect of the invention, said first element comprises an elongate apertured bar and said second element comprises weld filler material, said bar being connected to said surface processing tool via said weld filler material. 
     In accordance with a further aspect of the invention, said first element comprises an elongate apertured bar and said second element comprises a tool support bar or plate extending generally perpendicularly from said bar between its ends and rigidly attached thereto. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1  there is shown a conventional ride-on concrete finishing power trowel  10  comprising an operator seating and control station  12 , an engine  14 , at least two downwardly projecting spider assemblies  16 , each assembly having a plurality of radially extending, circumferentially spaced-apart spider arms and a trowel blade mounted on each arm for providing at least two sets of horizontal rotating blades encircled by a guard ring cage  18 . The adjacent spider assemblies  16  counterrotate, with one rotating clockwise and the other rotating counterclockwise. A typical four arm spider assembly  30 , suitable for use with either a ride-on or walk-behind power trowel, is illustrated in  FIG. 2 . The assembly includes four radially extending arms  32  emanating from a central hub  34 , which receives a drive shaft (not shown). Each spider arm  32  includes a pivot assembly  35  which allows the arm  32  to pivot about its longitudinal axis L. A trowel blade  36  is mounted via threaded bolts  38  (and lock washers and hex nuts, if desired) below each spider arm  32  in threaded apertures  40  spaced along and extending through each spider arm  32 . It will be appreciated that each rotor assembly may contain more or less than four arms for mounting trowel blades thereon, the number of arms being a matter of design choice. 
     The present invention provides a solution to the problem of surface processing tools wearing unevenly and to the problem of spider arm tendency to pivot which prevents free and unimpeded rotation of rotatable surface processing tools. According to the present invention these problems are overcome by providing a mounting adapter for mounting the rotational or longitudinal axis of the surface processing tool circumferentially behind the trailing side of the spider arm. It has been found that offsetting the surface processing tool circumferentially behind the trailing side of a spider arm controls the tendency of the spider arm to pitch into a trailing side down position. It will be appreciated, of course, that the side of a spider arm which is the trailing side is a function of the direction of rotation, clockwise or counter-clockwise, of the spider assembly. It follows that the trailing side when the rotation is clockwise becomes the leading side if the rotation is counter-clockwise. The mounting adapter of the present invention comprises a first means for attaching the adapter to the spider arm, desirably to the top or bottom surface of the spider arm, and a second means for positioning the rotational or longitudinal axis of the surface processing tool circumferentially behind the trailing side of the spider arm. Desirably the first and second means comprising the adapter are unitary and planar but, alternatively, may be separate structures rigidly attached via well known connecting means, such as welds, bolts, and the like. 
     It will also be appreciated that although the mounting adapter of the present invention will be described herein with reference to ride-on surface processing machines due to the unique advantage they offer in terms of square feet of concrete which can be finished per day, the mounting adapter can, of course, be used with walk-behind surface processing machines which also conventionally use downwardly projecting rotor or spider assemblies for mounting trowel blades. In addition, although the present invention will be described herein primarily with reference to circular brushes as illustrative of rotatable surface processing tools and grinding stone holders as illustrative of non-rotatable surface processing tools, it will be appreciated that the mounting adapter of the present invention can, of course, be used with other surface processing tools, such as scrubbers, buffers, grinders, polishers, and the like. 
     Referring to  FIG. 5A  and  FIG. 5B  there are illustrated two preferred embodiments, in the form of offset mounting plates  100 , of an offset mounting adapter of the present invention. Fundamentally, they differ only in size to accommodate the differing lengths of spider arms in spider assemblies. In one form, each offset mounting plate  100  has the general shape of a cleaver including an elongate handle  102  which merges into a wider offset blade portion  104 , which blade portion  104  extends in width in a direction generally perpendicular to the longitudinal axis  106  of the handle  102 . Handle  102  includes apertures  108  for attachment of the handle  102  to the spider arm  32 , desirably using at least two bolts, which extend through apertures in the spider arms and are received in apertures  108 , and offset blade portion  104  includes at least one aperture  110  for attachment to and positioning the surface processing tool or bearing therefor. Apertures  108  and  110  are desirably threaded to facilitate mounting a surface processing tool or bearing thereto using a threaded bolt or the threaded end of the central shank of a typical rotary bearing  80  (and lock washers and hex nuts, if desired). 
     Mounting plate  100  is configured for easily attaching above or below spider arm  32 , to provide an offset portion  104  to which a surface processing tool is mounted for positioning the rotational or longitudinal axis thereof (depending upon the type of the particular surface processing tool) circumferentially behind the trailing side  32   b  of spider arm  32 , and to not interfere with pivot assembly  35  associated with each spider arm  32 . One advantage of attaching the mounting adapter of the present invention to the top surface of the spider arm is that it reduces any tendency of a surface finishing tool to destabilize a troweling machine by raising its center of gravity. This sometimes occurs because surface finishing tools are considerably thicker than trowel blades and, therefore, when a spider arm pivots to a trailing edge down position, the thickness of the surface processing tool supporting the troweling machine on the tool&#39;s trailing portions raises the troweling machine considerably more than would a trowel blade supporting the machine on its trailing edge. It will be appreciated that the spider assemblies of troweling machines of different manufacturers have different configurations and that the shape of the offset blade portion  104  must be adapted to not interfere with spider assembly components. In the embodiments of  FIG. 5A  and  FIG. 5B  the length of offset blade portion  104  is shortened to not interfere with pivot assembly  35  of a spider assembly, e.g. a Wacker Neuson spider assembly, and comprises about ⅔ of the overall length of the offset mounting plate  100 . However, for use with troweling machines of other manufacturers, which may have different spider assembly configurations, the offset blade portion  104  might extend the entire length of the handle  102  or might be otherwise configured to accommodate the spider assembly configuration. 
       FIG. 6  illustrates the manner in which offset mounting plate  100  mounts onto the central shank of a typical rotary bearing  80  of a circular brush using a lock washer and hex nut, or equivalent connectors. When the configuration of  FIG. 6  is mounted to a spider arm via apertures  108  in the plate  100 , the bearing (and, therefore, the surface processing tool to which the bearing is affixed) is no longer positioned with its rotational axis in vertical registry with and directly beneath the spider arm as is the case with conventional mounting adapters. Rather, it is positioned with its rotational axis circumferentially offset from and behind the trailing side of the spider arm  32 . 
     Referring to  FIG. 7  and  FIG. 8  there is shown a typical circular brush assembly  50  including a circular bristle brush  52  in the form of a ring having a hollow center (not shown) mounted to or with the bristles extending from the underside  56   a  of a brush cover plate  56 , which has an upper surface  56   b  which may be flat or slightly convex. Cover plate  56  includes a central aperture (shown as  58  in  FIG. 11 ) for receiving a mounting shank of a typical rotary bearing  80  therethrough. A brush assembly  50  is mounted to one of the arms  32  of a spider assembly  30  by first mounting the brush assembly to aperture  110  of an offset mounting plate  100 , which itself is mounted below ( FIG. 7 ) or above ( FIG. 8 ) arm  32  of the spider assembly  30 . Brush assembly  50  is thereby mounted with its rotational axis offset to the rear of the trailing side  32   b  of the spider arm  32 , which can be clearly seen in  FIG. 9  as spider arm  32  rotates clockwise and in  FIG. 10  as spider arm  32  rotates counterclockwise. Brush assembly  50  is mounted to offset mounting plate  100  in a manner which allows brush assembly  50  to lie flat on the concrete surface and to spin freely on its axis, as will be seen from the following description. 
     Referring to  FIG. 11 , initially a rotary bearing  80  is mounted, e g., via bolts  74  and nuts  76 , on the upper surface  56   b  of brush cover plate  56  and positioned thereon such that bearing  80  is concentric with the central aperture  58  of the brush assembly  50 . Bearing  80  may be any type of bearing, e.g., ball bearing, roller bearing, fluid bearing, magnetic bearing, etc., which will permit each of the brushes  52  on each spider arm  32  to spin freely about its mounting axis perpendicular to the arms. In one illustrative embodiment, bearing  80  includes a stationary hub  82  having a central bore  83 , which is mounted to the brush cover plate upper surface  56   b , a rotating hub  84  having a central bore  85  mounted within the central bore  83  of stationary hub  82  and fluid bearing means  86  sealed within bearing  80  and between hubs  82 ,  84  to facilitate concentric rotation of the hubs about a common axis, which is the central axis  59  of the brush assembly central aperture  58 . A threaded, radially extending lubrication port (not shown) is desirably formed in stationary hub  82  to facilitate the injection of lubricant, when required. The lubrication port is closed by a grease port through which the lubricant may be injected. 
     With bearing  80  bolted in place on the upper surface  56   b , end  70  of mounting shank  60  is inserted into the central aperture  58  of cover plate  56  from the brush side of cover plate  56  and extends through central bore  85  of rotating hub  84  with threaded portion  68  of shank  60  emerging from the central bore  85 . The diameter of shank head  62  approximates the diameter of central aperture  58  but is slightly smaller so that the portion of head  62  which remains within central aperture  58  when shank  60  is fully inserted within rotating hub  82  does not frictionally engage the side walls of central aperture  58  as brush assembly  50  spins on mounting shank  60 . Cylindrical shank portion  66  has a smaller diameter than shank head  62  to define an annular shoulder  63  therebetween which seats against the underside of rotating hub  84  when mounting shank  60  is fully inserted therewithin. Cylindrical shank portion  66  has a diameter which allows central aperture  58  of brush assembly  50  to rotate freely about shank head  62  with just enough play to allow bearing  80  to absorb forces encountered during use, such as brush  52  striking bumps on the floor or brush cover plate  56  impacting with walls, and the like. Shank  60  is so dimensioned that, when thus mounted, the smooth portion  66  of mounting shank  60  is rotationally closely adjacent the inner diameter of rotating hub  84  and the brush assembly  50  is securely mounted on offset mounting plate  100 , yet is free to spin on the axis provided by mounting shank  60 . The threaded portion  68  projecting from rotating hub  84  is threaded or inserted into aperture  110  in offset portion  104  of mounting plate  100  and may be retained using a lock washer and hex nut, or equivalent hardware. In this manner, mounting shank  60  is firmly seated between the underside of rotating hub  84  and offset mounting plate  100 . Mounting plate  100  is attached via apertures  108  in handle  102  to spider arm  32  with bolts, as hereinbefore described. A recessed aperture  88 , such as a hexagonal aperture, is formed in end  64  of mounting shank  60  to facilitate threading or inserting threaded portion  68  of shank  60  onto offset mounting plate  100 . 
     Mounting the surface processing tool to the offset mounting plate  100  instead of directly to the spider arm  32  or indirectly to the spider arm  32  via one side rather than to the top or bottom of a mounting bar, positions the rotational axis of the tool behind the trailing side  32   b  of the spider arm  32  instead of in vertical registry with the longitudinal axis L of the spider arm  32  and overcomes the trailing side  32   b  down tendency of the spider arms  32 . This allows the bearing  80  of rotational surface processing tools to operate normally and to freely rotate and causes the surface processing tools to operate while oriented flat on the concrete surface. See  FIG. 7 . As a result, the surface finishing tools wear uniformly rather than unevenly and undesirable swirls and marks on the concrete surface are avoided. 
     A comparable result is achieved with surface finishing tools which do not rotate and, therefore, do not have a rotational axis or require a bearing to be mounted between the tool and the spider arm. Referring to  FIG. 12  and  FIG. 13 , mounting of nonrotating surface-finishing tools, such as grinding stones  120  in grinding stone holders  122 , are observed to wear more uniformly and, therefore, to be useful for a longer period of time, if the holder  122  is mounted to the offset portion  104  of offset mounting plate  100  of the present invention and the mounting plate  100  is mounted to the bottom ( FIG. 12 ) or top ( FIG. 13 ) of the spider arm  32 , as compared to the longitudinal axis  124  of holder  122  being mounted directly to and in vertical registry with the longitudinal axis L of the spider arm  32 . As with the circular brushes hereinbefore described, mounting to the offset mounting plate  100  mounts the longitudinal axis of the surface-finishing tool offset to the circumferential rear of the trailing side  32   b  of the spider arm  32 , which can be seen in  FIG. 12  and  FIG. 13  as spider arm  32  rotates clockwise. In  FIG. 12  and  FIG. 13 , the upper surface of grinding stone holder  122  is welded to the underside of offset blade portion  104 . Alternatively, grinding stone holder  122  could be attached to the offset blade portion  104  by providing one or more additional apertures (not shown) in the offset blade portion  104  and attaching the grinding stone holder via bolts extending upwardly through aperture  110  and through the additional apertures from the inside or grinding stone side of the holder  122 . 
     As indicated previously herein, the mounting adapter of the present invention comprises a first means for attaching the adapter to the spider arm and a second means for positioning the rotational or longitudinal axis of the surface processing tool circumferentially behind the trailing side of the spider arm. This allows the bearing of rotational surface processing tools to freely rotate and not bind and causes both rotational and non-rotational surface processing tools to operate while oriented flat on the concrete surface, thereby avoiding uneven wear and a shorter useful life. To achieve this goal it has been found advantageous to utilize the offset mounting plate  100  which has been described hereinabove and as illustrated in  FIG. 12  and  FIG. 13 . However, other mounting adapter configurations provide comparable results. For example, referring to  FIG. 14 , a grinding stone holder  122  may be welded along one of its elongate sides  122   a  to the side of a mounting bar  130  provided with apertures  132  for attaching the grinding stone holder  122  behind the trailing side  32   b  of the spider arm  32  instead of in vertical registry with the longitudinal axis L of the spider arm  32 . The mounting bar provides the first means for attaching the mounting adapter to the spider arm  32  and the weld filler material  134  comprises the second means for positioning the longitudinal axis of the holder  122  circumferentially behind the trailing side  32   b  of the spider arm  32 . Use of a mounting adapter such as this also allows the surface processing tool to operate while oriented flat on the concrete surface, as can be seen in  FIG. 15 , thus avoiding uneven wear and a shorter useful life In still another configuration, shown in  FIG. 16 , a mounting adapter can comprise a mounting bar, such as bar  130  which includes apertures  132  for attaching the mounting bar  130  to a spider arm  32  and, desirably, one or more apertures, such as apertures  132  or others, not shown, for rigidly attaching a surface processing tool positioning means, such as a tool support bar  136  or plate  136  (shown in phantom), to mounting bar  130  via one or more bolts or other rigid securing means. Support bar or plate  136  extends generally perpendicularly from mounting bar  130  in a direction circumferentially behind the trailing side  32   b  of spider arm  32  for mounting the rotatable or longitudinal axis of a surface processing tool, such as the threaded shank  68  of a rotatable bearing  80  attached to a rotatable surface processing tool. See  FIG. 16 . It will be appreciated that tool support bar or plate  136  may be of any convenient dimensions consistent with the dimensions and operation of the spider assembly and, also, comprehends the use of multiple bars or plates. 
     While the present invention has been described in terms of specific embodiments thereof, it will be understood that no limitations are intended to the details of construction or design other than as defined in the appended claims.