Abstract:
A powered jamb saw is provided which is ideally suited for making corner cuts. A cylindrical housing for the shaft of the circular saw blade is mounted in a split bushing tensioned by a threaded bolt secured to and for rotation by a handle positioned so as to permit the workman to use both hands to position the jamb saw during its use in making cuts.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a powered hand tool for trimming door jambs and casings. Door jambs and casings are often installed before the flooring is laid and for that reason the door joints and casings must be trimmed to a predetermined distance above the sub-floor in order to install the flooring which extends beneath the door jambs and casings. U.S. Pat. Nos. 5,967,013 and 6,449,852 describe jamb saws described as useful for door jamb and casing trimming including trimming in corners. The jamb saws shown in the before mentioned patents and door jamb saws currently marketed are deficient in adaptability for connection to a power unit, are awkward to hold and operate and are not convenient to adjust the height of cut. 
     SUMMARY OF THE INVENTION 
     The invention is a hand held power tool for trimming door jambs and casing and particularly a jamb saw attachable to a power tool having a rotary output shaft. The jamb saw includes a circle saw blade secured to a shaft rotatably mounted in a cylindrical shaft support column which in turn is supported in a vertically split bushing portion of a blade housing in a vertically adjustable manner and the blade housing is supported on three floor engageable rollers. The shaft support column and the bushing portion have cooperating guide components permitting relative vertical movement and preventing relative rotary movement. After adjusting the height of the saw blade, by vertically adjusting the saw blade support column relative to the blade housing, the split bushing portion is contracted by rotating a threaded bolt interconnecting circumferentially confronting segments of the split bushing portion. Rotation of the bolt is effected by a hand held tensioning handle rigidly secured to the unthreaded end of the bolt. In using the jamb saw, one hand grips the power tool and the other hand grips the tensioning handle thereby facilitating efficient positioning and accurate operation of the jamb saw. A pair of roller arms have first ends pivotally mounted to the housing on vertical axes and second ends each supporting a floor engageable roller. The roller arms are biased to diametrically opposite positions relative to the saw drive shaft and are retractable against the bias during use of the jamb saw in making corner cuts. Releasable coupling components are provided on the upper end of saw shaft and the power tool output shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is illustrated in the accompanying drawings in which: 
         FIG. 1  shows the jamb saw powered by an electric powered screw gun; 
         FIG. 2  is a section taken on line  2 - 2  in  FIG. 1 ; 
         FIG. 3  is a side view of the jamb saw; 
         FIG. 4  is a section taken on line  4 - 4  in  FIG. 3 ; 
         FIG. 5  is a vertical section of a roller and its support arm; 
         FIG. 6 and 7  are perspectives of a shaft coupler; 
         FIG. 8  is a perspective of a saw guard; 
         FIG. 9  is a top view of the jamb saw approaching a corner with parts broken away for illustration purposes, and 
         FIG. 10  is a top view similar to  FIG. 9  showing the jamb saw engaged in a corner cut. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows the jamb saw  11  of this invention powered by a modified screw gun  12 . Referring also to  FIGS. 2 ,  3 ,  4 ,  9  and  10 , the jamb saw  11  has a support structure  13  including a housing  14  partially sheltering a circular saw blade  15 . The housing  14  includes a horizontal roof  16  having a  150  degree arc shaped edge  17  concentric with the axis  18  of the saw blade  15  and straight edges  21 ,  22  at a right angle to one another extending in a converging manner from the ends of the arc shaped edge  17 . The roof  16  terminates in a forward edge  24  disposed at 45 degrees to the straight edges  21 ,  22  which terminate at equal distances from their theoretical point of convergence. 
     The housing  14  includes a block shaped bushing  31  having a lower part  32  which is rigidly secured by fasteners in the form of screws  26  to the roof  16  and includes a cylindrical vertical bore  35  concentric with a cylindrical vertical bore  35 ′ in the roof  16 . The bores are concentric with the axis  18  of the saw  15 . A vertical front face  25  of the bushing  31  is aligned with the forward edge  24  of the roof  16 . The bushing  31  includes an upper split bushing part  33  partially separated from the lower part  32  by a horizontal gap resulting from a horizontal cut extending across slightly more than half the horizontal width of the annular bore  41  formed in the bushing  31 . A vertically adjustable cylindrical shaft housing  34  is mounted in the annular bore  41 . The split bushing part  33  includes a pair of circumferentially spaced confronting segments  36 ,  37  which, when drawn toward one another by an adjustable tension mechanism, prevent axial and rotatational movement of the shaft housing  34 . 
     As shown in  FIGS. 3 and 4 , the split bushing segments  36 ,  37  include aligned horizontal bores  46 ,  47  and the adjustable tension mechanism includes a tension bolt  48  extending through the bores  46 ,  46  and through a bore  51  in a handle  52 . A pine  53  secures the handle  52  to the tension bolt  48 . The tension bolt  48  includes a threaded end in threaded engagement with a square nut  56  nonrotatably nested in a quadrilateral recess  57  in the bushing segment  36 . When the handle  52  is rotated counter clockwise to a horizontal position, as viewed in  FIGS. 2 and 3 , the bushing segments  36 ,  37  are drawn toward one another thereby securing the bushing  31  to the cylindrical shaft housing  34 . In its horizontal position, the handle  52  can be griped by the workers left hand during a cutting operation with the jamb saw  11 . Rotating the lever clockwise, as viewed in  FIGS. 2 and 3 , loosens the bushing  31  from the cylindrical shaft housing  34 , permitting the housing  34  and the saw blade  15  to be raised or lowered relative to the shaft housing  14 , thus adjusting the height of the cut made by the blade  15 . As shown in  FIG. 2 , the saw blade  15  is releasably secured by a screw  54  to a vertical shaft  56  mounted in the shaft housing  34  by a pair of vertically spaced anti-friction bearings  57 ,  58 . A coupler  61  is nonrotatably secured to the upper end of the shaft  56  and the coupler  61  is meshable with a similar coupler  62  secured to the output shaft  63  of the screw gun  12 . During an adjustment of the height of the saw cut, a guide mechanism including a vertical grove  66  in exterior of the shaft housing  34  and a registering set screw  67  in the bushing  31  prevent relative rotation of the shaft housing  34  and the bushing  31 . 
     The jamb saw  11  is supported on three spherical rollers  71 ,  72 ,  73 . Roller  71  is mounted in a central rear position on a rearward projection  74  of the housing  14 . Rollers  72 ,  73  are mounted in vertically oriented cylindrical housings  76 ,  77 , respectively, which in turn are secured to horizontally extending arms  78 ,  79  pivotally connected on vertical axes to laterally opposite portions of the roof  16  of the housing  14 . Roller  73 , housing  77  and arm  79  are shown in vertical section in  FIG. 5 . The arms  78 ,  79  are biased by springs  81 ,  82  to their arm extended positions shown in  FIG. 9  in which arm abutments  83 ,  84  contact opposite vertical sides of the quadrilateral shaped bushing  31 . As shown in  FIG. 10 , the straight edges  21 ,  22  of the housing  14  limit the depth of the corner cut by the jamb saw. The edges  21 ,  22  are also useful in limiting the depth of cut in side wall casings. 
       FIGS. 6 and 7  show the construction of the three prong driving couplers  61 ,  62 . As shown in  FIG. 2 , an externally threaded cylindrical insert  75  is in threaded engagement with internal threads in the upper end of the shaft housing  34  and a set screw  80  retains the insert  75 . The insert  75  aligns the couplers  61 ,  62 . A swing guard  89  for the saw blade  15  is shown in  FIGS. 1 ,  2 ,  3  and  8 . As shown in  FIG. 2  the swing guard  89  is rotatably secured to the cylindrical shaft housing  34  by snap rings  92 ,  93  and the swing guard  89  is biased to its blade guarding position shown in  FIG. 1  by a coil spring  94  encircling the shaft housing  34  with ends inserted in appropriate openings in the shaft housing  34  and the swing guard  89 . 
     The illustrated and hereinbefore described jamb saw  11  is an efficient, easy to use tool for trimming casings and door jambs. The 90 degree edges  21 ,  22  serve to guide and limit the depth of the cut. The height of the cut can be quickly changed by rotating the handle  52 , adjusting the vertical position of the shaft housing  34  and then rotating the handle  52  to tighten the split bushing  31  on the shaft housing  34 . In making a cut with the jamb saw, the workman has his right hand on the screw gun  12  and his left hand on the lever  52 . He holds the swing guard  89  in its retraced position shown in  FIGS. 9 and 10  by engaging an upstanding lever  91  on the swing guard  89  with the index finger of his left hand. Using both hands in operating the jamb saw contributes to safe efficient use of the jamb saw. In the full corner cut position shown in  FIG. 10 , the swing guard lever  91  nests within a recess  96  in the roof  16  of the housing  14  and is flush with the edge  21  of the roof  16 . The recess is clearly shown in  FIG. 1 .