This application claims the benefit of U.S. application No. 60/843,408, filed on Sep. 11, 2006. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to equipment for construction and road cuts, in particular to dust shrouds and dust collectors for portable slab saws, in particular for pavement cutting and the like. 
     BACKGROUND OF PRIOR ART 
     Slab saws are commonly used for generating cuts in pavement, stone and other hard surfaces typically found in outside environments. A typical slab saw includes a frame supported by wheels, a power unit for driving the saw, such as a gas or diesel motor, and a rotary blade. Pavement cuts formed by a slab saw may be used for a variety of purposes, including forming a narrow trench for installation of cables. In one application, a slab saw may be used to cut through an overlying pavement layer into the sub-grade material. Conventionally, this has been carried out via a wet-cutting process, involving directing a stream of water onto the saw blade for cooling and to wash away the dust generated by the cutting action. Wet-cutting of this type typically generates a relatively large volume of mud, which requires cleaning and disposal. As well, wet-cutting typically deposits a layer of mud on the walls of the cut. In certain applications, it is desirable to provide a clean cut, for example where the resulting cut is used for installation of cables and the like. For this application, the deposited mud layer must be cleaned from the inside of the cut, which requires considerable effort and water. It is therefore desirable to provide a dry cutting method, which leaves a relatively clean cut while also permitting easier removal and disposal of the dust resulting from the cutting operation. However, a challenge in providing a dry cutting method is to evacuate the dust generated by the blade in an easy and convenient manner. 
     Circular saws for carpentry use typically include a full or partial shroud for trapping of dust. The shroud may communicate with a vacuum source, for disposal of the dust. An example of a carpenter&#39;s saw of this type is shown in U.S. Pat. No. 5,327,649, to Sklower. A dust shroud for a portable circular saw is also described in U.S. Pat. No. 4,241,505, to Bodycomb, Jr., et al., which describes a portable circular saw having a two-part dust shroud consisting of upper and lower housings, joined together by an external attachment link. The housings are spaced apart, to permit a workpiece to be received between the housings during cutting 
     Dust collection shrouds for circular saws are also disclosed in U.S. Pat. No. 4,255,995 to Connor, U.S. Pat. No. 4,063,478 to Stuy and U.S. Pat. No. 4,253,362 to Olson. 
     Circular saws for carpentry, while often including a shroud for collecting dust, differ from slab saws for pavement cutting. Slab saws present different challenges from carpentry saws for preventing dust dispersal. Hence, there is a need for a convenient system for containing and removing dust during operation of a slab saw. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved housing for collecting dust from a slab saw of the type used in cutting pavement or the like. It is a further object to provide an improved system that includes the improved housing, together with a vacuum source and dust filter. It is a further object to provide a method for dry cutting of pavement with a slab saw while removing dust generated during the cutting operation. 
     In one aspect, the invention relates to a dust collection system for use with a slab saw. The system comprises a dust collector housing having upper and lower parts that telescope or otherwise selectively extend apart from each other or retract together so as to vary the effective height of the housing. The housing has an at least partly open front and bottom faces to permit a portion of the circular blade to enter the housing on the upswing so as to discharge dust-laden air into the housing interior. The housing communicates with a vacuum source so as to withdraw the dust-laden generated by the blade. 
     Optionally, the upper part of the housing includes a baffle to direct dust into the interior of the housing. Optionally, the housing communicates with a duct that extends at covers at least a portion of the rear wall of the housing and communicates with the housing interior through a slotted opening opposed to the blade. The duct may comprise telescoping portions integrated with the upper and lower housing parts, so as to permit the duct to cover portions of both the upper and lower housings. 
     The invention also comprises a method of dry-cutting pavement or similar hard material, using a slab saw that optionally cuts fully through the pavement into the sub-grade below to leave a dry trench. The method involves integrating a dust collection system of the type described herein with a slab saw and a vacuum source, generating a vacuum within the dust collection compartment while dry-cutting a trench, and filtering at least a portion of the particulates from the air stream captured by the system. A portion of the saw blade enters the compartment on the upswing portion of its rotation and draws at least a portion of the dust and particulates generated by the cutting operation into the compartment, for removal via the vacuum source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side elevation view, partly in section, of a system according to the present invention in operation, generating a cut through a section of pavement. 
         FIG. 2  is a perspective view of a dust collector according to the invention. 
         FIG. 3  is a perspective view according to  FIG. 2 , with the parts shown in exploded view. 
         FIG. 4  is a perspective view of the upper dust collector portion of the device, together with a circular blade. 
         FIG. 5  is an exploded view of the portion shown in  FIG. 4 . 
         FIG. 6  is a bottom plan view of the upper portion of the dust collector. 
         FIG. 7  is a side elevational view of the upper portion of the dust collector, with a side panel removed to show internal features, and showing a circular saw blade for reference. 
         FIG. 8  is a perspective view of the lower portion of the dust collector. 
         FIG. 9  is an exploded view of the portion shown in  FIG. 8 . 
         FIGS. 9A and 9B  are bottom and side elevational views respectively of the lower compartment portion. 
         FIG. 10  is a side elevational view of a further embodiment, showing internal structure. 
         FIG. 11  is a perspective view of the embodiment of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , the dust collector  10  described herein is intended to be connected to a conventional vacuum source and dust filter unit  8 , which may comprise a fan unit  160 , coupled with a filtration unit  162  such as a filter bag. As will be apparent, any suitable type of vacuum and dust filter unit may be provided, or in the alternative, the source may supply only a vacuum and the collector may simply exhaust the removed dust away from the user, for example if the device is to be used in an inside environment and a centralized remote filtration unit is provided. However, it is contemplated that a suitable use for the present invention is for dry-cutting of pavement, or other outdoor surface, using a slab saw to cut into the pavement or other similar surface. Typically, such applications raise significant amounts of dust that must be filtered to prevent the dust from entering into the local environment. In one non-limiting example, the dust collector unit supplies 1100 cfm vacuum. 
     The dust collector is intended to form a component of a system that also includes a slab saw  170  for dry cutting of pavement, and a vacuum/filter unit  8  for generating an airflow through the collector  10  and filtering the air prior to discharge. Slab saw  170  includes a frame supported by wheels  171 . 
     A first embodiment is illustrated in  FIGS. 2 through 9 . 
     Turning to  FIGS. 2 and 3 , the dust collector  10  comprises generally an upper housing  12  and a lower housing  14 , a portion of which is disposed within the upper housing and telescopes downwardly therefrom so as to adjust the effective overall height of the collector to accommodate blades of different diameters. A vacuum duct  90  communicates with the collector  10 , which in turn provides a source of suction from the vacuum source  8 . 
     The upper housing  12 , seen in more detail in  FIGS. 4 and 5 , comprises a generally rectangular structure having flat sides  20 , an open front  22  for receiving a portion of a circular blade  18  within the interior of the housing  12 , a closed top  24 , a rear enclosure  26  comprising a tubular member and an open base  28 . The blade  18  enters the housing through the open base and front. The sides  20  comprise two spaced apart rigid side panels which define an interior space therebetween. The panels  20  may be rectangular, as illustrated, although it will be readily seen that they may take on essentially any convenient shape. However, the rectangular shape shown in the figures is convenient since, amongst other advantages, this shape readily permits the telescoping feature described herein, and is thus particularly suited for the present invention. The opposed panels  20  are joined together by way of opposing flaps  30  and  32  extending from the upper edge of each panel. The respective flaps  30 ,  32  face each other, and when assembled the flaps overlap. The overlapping flaps form an upper substantially sealed lid of the housing  12 , to partly enclose the interior space. The flaps  30  and  32  are held together by means of bolts or the like (not shown), extending through aligned apertures within the flaps. 
     The rear enclosure  26  of the upper housing  12  terminates at its upper end in a generally cylindrical tubular connector member  42  extending upwardly from the rear portion from the housing  12 . The enclosure  26  thus effectively forms an extension of the duct  90  so as to permit a relatively smooth and laminar flow of air through the system. The enclosure  26  includes a vertically extending slotted opening  36  in its lower region  40  to communicate with the interior of the upper housing  12 . The connector  42  extends upwardly above the sides  20 , and is cylindrical for connecting with a suitably dimensioned vacuum duct. The lower end  44  of the enclosure  26  is open, to receive a corresponding lower enclosure  74  of the lower portion  14  in a sliding engagement. The enclosure  26  is fastened to the side panels  20 , for example by welding, such that the slotted opening  36  in the tubular member has the same width as the spacing between the side panels  20  and is aligned therewith. 
     The upper housing  12  is provided with an internal baffle  50 , housed within the interior space between the respective upper panels  20 , and positioned at the upper end thereof. The baffle  50  is generally V-shaped when seen from the side. The baffle has a side-to-side width which is the same as the spacing between the side panels  20 , to permit it to fit snugly within the interior of the housing  20 . The baffle comprises a pair of diverging flat plates  52 , the upper edges of which turn inwardly to form opposing flanges  54 , which provide mounting surfaces such that the baffle may be conveniently bolted, screwed or otherwise fasted to the flaps  30  and  32  of the side plates  20 . The lower edges of the baffle plates  52  converge towards a point  56  when seen from the side. The baffle is mounted within the dust collector such that one plate  52  faces the circular blade  18 , leaving gap to provide clearance for the blade. In one aspect, the baffle  50  is removable, and a kit comprising several different sizes of baffles  50  is provided to accommodate circular blades of different diameters. The function of the baffle  50  is to reduce the amount of dust escaping the upper collector, by directing the dust-laden airflow towards the back of the collector where it may enter the duct for removal. 
     The collector  10  is mountable to a slab saw  170  via a pivot mount  60  mounted to upper housing  12  near the top front corner thereof. The mount  60  consists of opposing plates  62 , having therein aligned apertures  64  therein for receiving a hinge pin, not shown. The mount  60  permits the collector  10  to be pivotally mounted to a slab saw  170  such that the dust collector structure may be pivoted upwardly and outwardly away from the saw when not in use; and then when in use, rotated back into the generally vertical position seen in  FIG. 1 . For example, the mount  60  may mount to the housing or support structure of a slab saw. When rotated into its use position, the blade  18  is partly enclosed between the opposed side panels  20  of the dust collector  10  such that when a sufficient vacuum is generated within the collector by the vacuum unit  160 , dust-laden air generated by the saw is largely drawn into and filtered within the dust collector unit  160 . 
     The lower housing  14  is slidably engaged to the upper housing  12  and telescopes downwardly therefrom when in the normal upright use position. The lower housing  14  is similar in shape to the upper housing  12 , but has somewhat smaller outside dimensions so as to fit within the interior of the upper housing so these components may fit snugly together with a sliding engagement. The lower housing has an open front  70 , an open top  72  to communicate with the upper housing, a closed partly cylindrical rear portion which comprises a tube  74 , and partly open bottom  76  to accommodate a circular saw blade. The lower housing  14  comprises opposed spaced apart panels  73  similar in configuration to those of the upper housing  12 , but spaced more closely together so as to slide within the interior space of the upper housing. The interiors of the upper and lower housing  12  and  14  communicate to form an uninterrupted hollow interior region that receives the circular saw blade. 
     A rigid vertically oriented elongate bar  77  is mounted to the outside surface of one of the panels  70  of the lower housing  14 , and is slidably received within a corresponding sleeve  79  on a corresponding side panel of the upper housing. The upper end of the bar  77  terminates in an outwardly-facing flange  76 , which serves as a stop to prevent the bar from sliding out from the sleeve  79 . The bar  77  is fastened within the sleeve by means of a threaded tightening shaft  78  having a handle  80  for operation by the user, which fits within a threaded aperture  82  within the sleeve  79 . The free end of the shaft  78  may simply press against the bar  77  to retain position by friction, or alternatively the bar  77  may include multiple recesses or apertures (not shown) to provide a more secure retention and fixed positions. 
     The bar  77  and sleeve  79  cooperate to form an adjustable retention means to retain the lower and upper housings  12  and  14  together in a selected fixed position. Loosening of the shaft  78  permits adjustment of these respective positions so as to adjust the overall height of the collector  10  to accommodate saw blades of different diameter. 
     The rear of the lower collector consists of a lower cylindrical member  74 , seen in  FIGS. 6 through 9B , the open interior of which communicates with the interior of the lower housing  14  in the same manner as the upper housing. The lower cylindrical member  74  includes a vertically extending slotted opening  81  extending from top to bottom thereof to communicate with the interior of the housing  14 . Preferably, the lower end  84  of the lower cylinder  74  is angled, as seen in  FIGS. 6 and 7 , so as to prevent denting or damage when the collector  10  is tilted rearwardly. The lower end  84  of the tubular member is capped with an lower tube cap  86 , which may be permanently fastened, or alternatively, removeably engaged to selectively seal the end of the lower tube, for example by means of a hinge  88 . 
     The opposing side panels  73  of the lower housing  14  terminate at their lower end, each with an inwardly facing flap  98  and  96 , in a similar fashion to the flaps  30  and  32  of the upper housing  12 . The opposing flaps  98  and  96  overlap and are joined together by fasteners such as screws (not shown). The lower flaps  98  and  96  cover only a rearward region of the lower housing. The forward region is open, to permit a saw blade to extend vertically below the structure while being partly received therein. 
     When assembled to the upper housing  12 , the lower and upper cylindrical members  74  and  26  slide one within the other, such that the lower tube  74  telescopes from the upper tube  26 . The respective tubes fit together with a snug fit to prevent air leakage. 
     Conveniently, the lower and upper housings  12  and  14  comprise sheet steel panels, and likewise the lower and upper tubes  26  and  74  comprise shaped sheet steel, which can be welded to the respective lower and upper housings  12  and  14 . Alternative materials and modes of attachment of these components may be employed, according to methods and techniques known to those skilled in the art. 
     The enclosure  26  of the upper housing  12  conveniently joins with a flexible or jointed duct  90  for communication with the vacuum source  160  to draw air through the collector. The vacuum source  160  generates sufficient airflow and negative pressure within the collector  10  so as to draw in substantially all of the dust and other particles generated by the slab saw  170  during normal operation of the saw. Preferably, the vacuum source also includes a filter for removing dust and other particles. For example, a four inch flexible or jointed metal duct  90  may be provided that fits onto the connector  42 , with suitable substantially airtight sealing or connection means being provided, not shown. 
     The vacuum source may comprise any conventional vacuum source capable of drawing a relatively high volume of air through the housing so as to minimize the escape of dust-laden air generated by the blade through the filter. The airflow provided by the vacuum source may be varied, depending on the particular application. Persons skilled in the art will readily be able to determine the appropriate airflow level for the selected application of the device. 
     A second embodiment is illustrated in  FIGS. 10 and 11 . In this version, the lower and upper housings  100 ,  102  each are generally rectangular in overall configuration. The rear panels of the housings comprise generally flat plates. The interiors of the upper and lower housings communicate to form an uninterrupted hollow interior region that receives the circular saw blade. As with the first embodiment, the front faces  104  of both housings are open, and the lower housing  100  has a partially open lower face  106 . The upper housing  102  includes a threaded coupling  108  at its upper rear corner, communicating with the interior of the compartments, to permit the threaded attachment of a duct (not shown). It will be seen that the threaded coupling  108  is but one convenient way to fasten a duct to the collectors; one skilled in the relevant art will understand that other types of couplers may be readily provided. 
     The rear lower corner  110  of the lower housing  100  is rounded and has a skid plate  112  mounted on the exterior surface of the rounded corner, to provide a ground contact surface that permits the collector  10  to slide along the ground. 
     The system includes a generally conventional slab saw  170 , which includes a wheeled housing having a power unit. The slab saw includes a circular blade  18 . It will be readily seen that essentially any type of circular blade  18  may be used in association with the invention. Although the collector may be used with a range of blade diameters, sizes and types, in one example, an 18″ diamond blade is provided, for cutting into pavement. 
     A use of the collector  10  is illustrated in  FIG. 1 . According to this aspect, the dust collector  10  may be used for dry-cutting of asphalt, concrete, or other pavement  120 . In one aspect, the trench-like cut  122  extends fully through the upper material into the sub-grade material  124 , for example packed soil or the like. An advantage of dry-cutting in this type of application, rather than using more conventional wet-cutting methods, is that the sub-grade material does not cave in after the saw passes through, thereby leaving behind a narrow trench  122 , substantially the width of the saw blade, in which the sidewalls of the cut are relatively clean and dry after the cut is made. In contrast, wet-cutting deposits a layer of mud on the walls of the cut, which requires significant effort and water to remove. As well, material removed from the dry cut is readily disposable, as it is in the form a dry dust which is filtered by the vacuum unit. In contrast, conventional wet-cutting generates mud, which requires special disposal methods. As well, dry-cutting dispenses with the requirement of transporting water tanks or locate water hook-ups or the like. 
     Thus, the use of slab saw to provide a narrow trench  122  that extends through the upper pavement level and into the sub-grade material provides a convenient and relatively inexpensive way to achieve a clean and dry cut. The width of the resulting trench will be determined by the width of the saw blade, with this depending on the desired application. For example, a narrow trench of this type may extend sufficiently below the pavement level to permit installation of one or more cables, such as fibre optic cables, within the resulting trench. Since these cables are entirely below the pavement level, the trench may then be partly filled with soil, sand, or the like, following which the pavement is fully restored to the full thickness of the original pavement. 
     It will be seen that the telescoping feature of the dust collector  10  permits it to be used in a variety of applications. For example, it permits the dust collector to be used with a variety of saw diameters. As well, pivoting of the dust collector relative to the saw assembly permits adjustment of the depth of the saw cut by varying the depth of blade extending below the dust collector  10 . Conveniently, the dust collector  10  is positioned to substantially contact the pavement surface when in use, so as to minimize any air gap between the pavement and dust collector. This minimizes any possible leakage of dust from around the dust collector. 
     The foregoing discussion and description is intended to illustrate the concepts of the invention by way of representative examples, with emphasis upon the preferred embodiment or embodiments. The above description is not exhaustive of all options or mannerisms for practicing the disclosed principles of the invention, the full scope of which includes this patent specification as a whole, including the claims thereof. The full scope of the invention also includes functional and mechanical equivalents of elements set forth herein, including elements described explicitly or by implication as being a means for carrying out of a defined task or end. The inventor hereby states that it is his intention to rely upon the doctrine of equivalents in protecting the full scope and spirit of the invention, and to not be limited to any means described with particularity herein, for carrying out of a specified function.
A dust collector is provided for use with a SLAB saw, especially suited for dry-cutting a channel within pavement or similar exterior surface. The collector includes telescoping upper and lower housings, an open front and lower base to receive a portion of a circular saw into the interior of the housing, and an exhaust outlet, for attaching to a vacuum duct, so as to exhaust dust-laden air from the interior of the housing. The housing includes a pivot mount, pivotally mounting the unit to a slab saw. Also provided is a system, including the dust collector with a circular saw and optionally a vacuum source and dust filter unit or units. Also provided is a method for dry-cutting a trench or channel within pavement or similar hard outside surface, which is particularly suitable for laying of cable such as fiber optic cable. The method may include the step of cutting through the pavement into the underlying hard-packed substrate.