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BACKGROUND 
       [0001]    The field of the invention is drywall knives. 
         [0002]    The art of applying drywall compound or “mud” to a taped drywall joint is highly specialized, often requiring months or years of practice to perfect. The drywall knife disclosed herein simplifies the process of mudding drywall joints. 
       SUMMARY 
       [0003]    One embodiment of the present drywall knife comprises a handle; a substantially planar, flexible blade attached to the handle; and a brace having a cross-member wherein the brace is attached to the handle and wherein the cross-member defines at least one substantially non-linear profile and imparts a substantially non-linear profile to the blade. The knife may further comprise the cross-member defining two or more substantially non-linear profiles, and the cross-member may be positionable to substantially impart different non-linear profiles selectively to the blade. The brace may be substantially T-shaped, and the brace may be retractable. 
         [0004]    In another embodiment, a drywall knife comprises a handle; a channel disposed within the handle; a substantially planar, flexible blade attached to the handle; and a T-shaped brace having a central post and a cross-member wherein the central post is slidably disposed within the channel of the handle and wherein the cross-member defines at least one profile wherein the blade is biased to rest against the cross-member such that the cross-member substantially imparts a profile to the blade. The profile imparted to the blade may be substantially non-linear, and the profile imparted to the blade may be substantially arcuate. Further, the cross-member may define at least two profiles, and the cross-member may be positionable to substantially impart different profiles selectively to the blade. The cross-member may further define knobby contact surfaces contactable with the blade. In addition, the blade may be hingedly attached to the handle, a tab may be attached to the blade, and a spring may be disposed between the tab and the handle. 
         [0005]    In yet another embodiment, a drywall knife comprises a handle; a channel disposed within the handle; a substantially planar, flexible blade hingedly attached to the handle; and a retractable T-shaped brace having a central post and a cross-member wherein the central post is slidably disposed within the channel of the handle, wherein the cross-member defines two or more substantially non-linear profiles, and wherein the blade is biased to rest against the cross-member such that the cross-member substantially imparts one of two or more substantially arcuate profiles to the blade. The cross-member may further define three substantially non-linear profiles. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a top planform view of an embodiment of a drywall knife with a brace. 
           [0007]      FIG. 2  is a side elevational view of an embodiment of a drywall knife with a brace. 
           [0008]      FIG. 3  is a bottom planform view of an embodiment of a drywall knife with a brace. 
           [0009]      FIG. 4  is a perspective view of an embodiment of a cross-member for a brace for use with a drywall knife. 
           [0010]      FIG. 5  is a front elevational view of an embodiment of a cross-member for a brace for use with a drywall knife. 
           [0011]      FIG. 6  is a perspective view of an embodiment of a cross-member for a brace for use with a drywall knife. 
           [0012]      FIG. 7  is a perspective view of an embodiment of a drywall knife with a brace in a retracted position. 
           [0013]      FIG. 8  is a perspective view of an embodiment of a drywall knife with a brace in an extended position. 
           [0014]      FIG. 9  is a perspective view of an embodiment of a drywall knife with a brace. 
           [0015]      FIG. 10  is a cut-away side elevational view of an embodiment of a drywall knife with a brace. 
           [0016]      FIG. 11  is a cut-away side elevational view of an embodiment of a drywall knife with a brace. 
           [0017]      FIG. 12  is an exploded perspective view of an embodiment of a drywall knife with a brace. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 1  shows a top planform view of a drywall knife  10 . The knife  10  has a handle  12  and a substantially planar, flexible blade  14  attached to the handle  12 . As shown in the drawing figures, the handle  12  has a generally cylindrical shape that is somewhat tapered, with the narrower end nearer to the blade  14  and the wider end away from the blade  14 , although the handle  12  may have any shape or size capable of being held by a human hand (not shown). As shown in  FIG. 2 , a side elevational view of the knife  10 , and in  FIG. 3 , a bottom planform view of the knife  10 , the handle  12  may have one or more curved portions  16  suitable for receiving one or more fingers of a hand when gripping the handle  12 . The handle  12  may also be constructed or formed so as to define a channel  18  running substantially longitudinally through the handle  12 . The channel  18  may terminate with an aperture  20  formed at the end of the handle  12  distal to the blade  14 . The handle  12  may be constructed from any suitable material. 
         [0019]    The blade  14  of the knife  10  is substantially planar and is substantially rectangular or trapezoidal in shape, defining a leading edge  22 , a rear edge  24 , and side edges  26 . The blade  14  may be made from any flexible material, however metal is likely to provide a longer service life for the blade, and steel or steel alloys are likely to produce blades with both suitable flexibility and longevity. Different embodiments of the knife  10  may be made with blades having differing sizes and stiffnesses, depending upon the intended application for each embodiment of the knife  10 . The size may vary in both overall planform area, as well as thickness. 
         [0020]    The rear edge  24  of the blade  14  may be stiffened or reinforced by a reinforcing member  28 . The reinforcing member  28  may comprise a single piece of material formed to wrap around the rear edge  24  of the blade  14  to define a bottom reinforcing element  30  and top reinforcing elements  32 . Portions of the reinforcing member  28  may also be formed to comprise one or more hinge portions  34 . In some embodiments, the reinforcing member  28  may also be formed to define a tab  36  that extends over a recessed portion  37  of the handle  12 . A spring  38  may be disposed between the tab  36  and the recessed portion  37  of the handle  12  as shown in  FIGS. 10 ,  11 , and  12 . The reinforcing member  28  may be made from metal or other suitable material. In some embodiments, the reinforcing member  28  may be comprised of multiple pieces of material. 
         [0021]    In reference to  FIGS. 1 ,  2 ,  3 , and  12 , the knife  10  also has a hinge carrier  39  with hinge portions  40 . The hinge portions  40  of the hinge carrier  39  are interlaced with the hinge portions  34  of the reinforcing member  28  to define a substantially tubular hinge channel or axis  41  through which a pin  42  may be inserted to establish a hinged connection  43  between the hinge carrier  39  and the reinforcing member  28 . The hinge carrier  39  also defines a collar  44  sized to fit within the handle  12 . The collar  44  may have a notch or hole  45  that aligns with a hole  46  in the handle  12  through which a pin  47  may be inserted to affix the hinge carrier  39  to the handle  12 . Alternatively, the collar  44  and the handle  12  may be attached in any suitable way, including, without limitation, overmolding or a threaded or friction-fit connection. The hinge carrier  39  and collar  44  further define a channel  48  substantially in axial alignment with the channel  18  in the handle  12 . The collar  44  also further defines a shoulder  49 . 
         [0022]    The knife  10  also has a brace  50  having a central post  52 , a hub  54 , and a cross-member  56 . The central post  52  is substantially rigid and substantially cylindrical in shape, although it may be formed in any suitable shape, and it is sized to be slidably disposed within the channel  48  of the hinge carrier  39  and collar  44 . A stop  58  may be attached to the end of the post  52  disposed within the channel  48  in order to limit the forward travel of the post  52  outside of the handle  12  by interfering with the shoulder  49  on the collar  44 . The hub  54  is connected to the end of the post  52  located away from the handle  12 , and may be integrally formed with the post  52  or may be separately formed and then attached to the post  52  by suitable means. The hub  54  also defines a bore  60 . 
         [0023]    As shown in  FIGS. 1 ,  2 , and  4 , the cross-member  56  has two arms  62  connected by a substantially cylindrical central portion  64  disposed through the bore  60  in the hub  54 . The central portion  64  and bore  60  are sized so that the cross-member  56  and central portion  64  are free to rotate within the hub  54 . The arms  62  of the cross-member  56  each have longitudinal lobes  66 ,  68 , and  70 . The lobes  66 ,  68 , and  70  also define contact surfaces  56   a ,  56   b , and  56   c . Contact surfaces  56   a  are formed from adjacent longitudinal lobes  66  and  70  such that when the cross-member  56  is positioned such that longitudinal lobes  66  and  70  are in contact with the blade  14 , contact surfaces  56   a  are positioned immediately adjacent to the blade  14 . Similarly, when adjacent longitudinal lobes  66  and  68  are in contact with the blade  14 , contact surfaces  56   b  are positioned immediate adjacent to the blade  14 . Finally, when adjacent longitudinal lobes  68  and  70  are in contact with the blade  14 , contact surfaces  56   c  are positioned immediate adjacent to the blade  14 . 
         [0024]    In one embodiment, the arms  62  of the cross-member  56  are tapered in such a way that the portions of the contact surfaces  56   a  nearest the central portion are not co-planar with the portions of the contact surfaces nearest the ends of the outer ends of the arms  62 . The contact surfaces  56   a  may thus define a non-linear profile when viewed in elevation as depicted in  FIG. 5 , and in some embodiments, the contact surfaces  56   a  may define a substantially arcuate profile (not shown). Similarly, in one embodiment, contact surfaces  56   b  and  56   c  are similarly formed to define non-linear profiles when viewed in elevation, and in some embodiments, contact surfaces  56   b  and  56   c  may define substantially arcuate profiles. In one embodiment, each of contact surfaces  56   a ,  56   b , and  56   c  define a different profile. Further, in some embodiments, one of the contact surfaces  56   a ,  56   b , and  56   c  may instead define a substantially planar profile. In some embodiments, as in those shown in  FIGS. 1 ,  2 ,  4 , and  5 , the contact surfaces  56   a ,  56   b , and  56   c  are substantially smooth. In other embodiments, as shown in  FIG. 6 , one or more of contact surfaces  56   a ,  56   b , and  56   c  may be formed to define one or more substantially rounded bumps or knobs  72 . 
         [0025]    As shown in  FIG. 7 , the knife  10  may be operated with the brace  50  and cross-member  56  in a refracted position, in which the central post  52  of the brace is substantially retracted into the channel  18  in the handle  12  such that the cross-member  56  abuts the hinge carrier  39  and rests adjacent to the top reinforcing elements  32  of the reinforcing member  28 . 
         [0026]    As shown in  FIGS. 8 and 10 , the knife  10  may be operated with the brace  50  and cross-member  56  in a fully extended position, in which the stop  58  abuts the shoulder  49  of the collar  44  of the hinge carrier  39 . In this position, the cross-member  56  rests against the blade  14  near its leading edge  22 . Viewing  FIG. 8  in connection with  FIG. 10 , a cut-away side elevation view of the knife  10 , the spring  38  is in compression between the tab  36  and the recessed portion of the handle  12 . Because the tab  36  is attached to the reinforcing member  28  and the blade  14 , the blade is biased against the contact surfaces  56   a  of the cross-member  56 . In embodiments where the contact surfaces  56   a  of the cross-member  56  substantially define a non-linear profile, when the knife  10  is drawn with sufficient force across one or more pieces of drywall (not shown) on which drywall compound (not shown) has been spread, the leading edge  22  of the flexible blade  14  of the knife  10  will impart a substantially non-linear profile to the drywall compound in what is known as a “feathered” application. 
         [0027]    In addition to the refracted configuration of the brace  50  as shown in  FIG. 7  and the fully extended configuration of the brace  50  as shown in  FIGS. 8 and 10 , the knife  10  may be operated with the brace  50  in any position between these extremes. In some embodiments, it may be desirable to remove the brace  50  altogether and use the knife  10  without the brace  50 . 
         [0028]    In order to change the position of the brace  50 , a user depresses the tab  36  on the reinforcing member  28  into the recessed portion  37  of the handle  12 , thereby compressing the spring  38 , as shown in  FIGS. 9 and 11 . Because the central post  52  of the brace  50  is slidably disposed within channel  48  of the hinge carrier  39  and channel  18  of the handle  12 , the user may slide the brace  50  to any position between the fully retracted and fully extended positions, inclusive. By releasing pressure on the tab  36 , the spring  38  will bias the tab  36  and reinforcing member  28  about the pin  42  in the hinge joint  43 , thus biasing the blade  14  against the cross-member  56 . 
         [0029]    In addition to changing the location of the brace  50  relative to the blade  14 , a user can also rotate the cross-member  56  of the brace  50  in order to selectively position any one of contact surfaces  56   a ,  56   b , or  56   c  against the blade  14 . In embodiments where each of contact surfaces  56   a ,  56   b , and  56   c  define different profiles, the knife  10  and blade  14  are thereby adjustable to impart differing profiles to the blade  14 . Further, in embodiments where knobs or bumps  72  are provided on one or more of contact surfaces  56   a ,  56   b , or  56   c , the knobs  72  assist in breaking the surface tension between the contact surface and the blade  14  in the event that some drywall compound overflows or is splashed on that interface. In alternative embodiments, surface relief other than knobs or bumps  72  may be used on one or more of contact surfaces  56   a ,  56   b , or  56   c  to achieve the same purpose. 
         [0030]    There are numerous alternative embodiments contemplated for the knife  10 . In one alternative embodiment, the brace  50  and cross-member  56  may be fixed in an extended position, and the hinge joint  43  and spring  38  may be omitted. In such an embodiment, the blade  14  may be sufficiently flexible such that the cross-member  56  may be selectively rotated against a fixed, biased position of the blade  14  against the cross-member  52 . In another embodiment, a structure different than a central post  52  may be used to position the cross-member  56  in either a fixed configuration or in a selectively retractable configuration relative to the blade  14 . In other embodiments, the cross-member  56  may define one or more contact surfaces defining one or more profiles, and in embodiments where the cross-member  56  defines more than one contact surfaces defining more than one profile, the cross-member  56  may be selectively positionable between the different contact surfaces. In these embodiments, there is no theoretical limit to the number of different profiles that may be so defined. 
         [0031]    While the knife  10  has been described in reference to some exemplary embodiments, these embodiments are not limiting and are not necessarily exclusive of each other, and it is contemplated that particular features of various embodiments may be omitted or combined for use with features of other embodiments while remaining within the scope of the invention.

Summary:
A drywall knife with a retractable brace is disclosed. The knife comprises a handle; a substantially planar, flexible blade hingedly attached to the handle; and a brace having a cross-member wherein the brace is attached to the handle and wherein the cross-member defines at least one substantially non-linear profile wherein the cross-member substantially imparts a substantially non-linear profile to the blade. The knife may further comprise the cross-member defining two or more substantially non-linear or arcuate profiles, and the cross-member may be positionable to substantially impart different non-linear profiles selectively to the blade. The cross-member may further define knobby contact surfaces contactable with the blade. The brace may be substantially T-shaped, and the brace may be retractable.