Abstract:
A corner finisher spreads mastic on a joint formed at an inside corner of drywall. The drywall corner finisher is conventionally used with a plurality of alternative tools for supplying a plurality of coats of mastic in different thicknesses. Therefore, a quick disconnect coupler is provided to rapidly change the tools and yet to hold them so securely that there is almost no chance for an unwanted disconnect between the drywall corner finisher and one of the alternative tools for supplying mastic. The invention provides such a coupler in the form of a ball and socket behind a sliding locking plate having a key hole slot in it for receiving a ball on a mastic delivery device.

Description:
This application is a continuation of application Ser. No. 08/229,479, filed Apr. 19, 1994, now abandoned. 
    
    
     This invention relates to tools for applying mastic to corners of drywall, and more particularly to fail safe quick disconnect couplers for such tools. 
     BACKGROUND OF THE INVENTION 
     Currently, drywall is almost universally used for interior walls in houses and buildings. The drywall comes in large sheets which are fitted together to make a solid wall surface having an appearance approximating the appearance of a plastered wall. The cracks between the sheets must be covered by a tape and mastic which is thereafter sanded to give the plastered wall appearance. 
     This means that, in the interior corners of the walls, it is necessary to fit the tape and mastic properly and almost perfectly along the 90° angle between the two walls that meet in the corner. The corner finisher tool should have enough freedom of movement to enable it to position and accommodate itself to irregularities on the wall surface. The tape should not either span the corner or fit into a crack between the wallboards. The mastic should be applied as smoothly as possible because it is difficult to sand off the excess mastic in the corner. An example of a prior art corner finisher tool is found in U.S. Pat. No. 4,767,297. 
     Among other things, there are many different kinds of tools which may be used for applying the tape and mastic to both the flat seams on a wall surface between drywall sheets and the corners where drywall sheets abut. Three coats of mastic are applied in different thicknesses over the tape. Therefore, there are many tools which are generally parts of a mastic application system and which should be changed quickly and easily as the workman encounters different needs during his work. 
     Therefore, it is a common practice to provide a quick disconnect coupler for joining the various drywall mastic applicator tools to each other. However, heretofore there have been problems because there were frequent failures of the locking mechanism on the coupler, such as for securing a corner finisher tool to other equipment for supplying a mastic. In particular, it was difficult to secure a corner finishing tool to a mastic source because the finisher tended to be larger and heavier than other tools, because the need for precision in the corners is much more severe than the need for precision on a strictly flat wall surface, and because the pressure of mastic being squeezed out of a pressurized delivery system tends to push the finisher off the tool for delivering the mastic. 
     The prior art used a U-shaped spring, into which a tool snapped, in order to solve the simultaneous problems of providing quick disconnect and secure locking after the connection was made. The troubles were multiplied because the corner finisher tool could easily separate from the associated tools and fall to the ground. The corner finisher tool then might be damaged. While the tool itself could be replaced, if the tool fell in a bathroom, for example, the ceramic tile, a bath tub, or another fixture could be chipped or otherwise severely damaged by the falling tool. These problems are often difficult and expensive to repair. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the invention is to provide new and improved locking means for quick disconnect means for securing tools to drywall mastic applicators. Here, an object is to provide a quick connect or disconnect means for reliably locking the tools on the applicator in a fail safe manner. In this connection, an object is to accomplish these and other objects at a cost which is almost the same as the cost of the prior art locking mechanism. 
     In keeping with an aspect of the invention, these and other objects are accomplished by providing a spring biased, sliding plate which has a somewhat key hole shaped slot therein. The plate is normally spring biased to cause it to slide to a position where a small end of the key hole slot is in a locking position to pass and capture a ball joint on the tool in a socket on another tool. When the plate is slid against the spring bias, the large end of the key hole slot is positioned over the ball joint so that it may be easily removed to replace one tool with another tool. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of this invention is seen in the attached drawings, wherein: 
     FIG. 1 schematically shows a corner finisher tool being used to apply mastic to an inside corner of a drywall; 
     FIG. 2 is an exploded view of a prior art corner finisher tool shown in U.S. Pat. No. 4,767,297; 
     FIG. 3 is a plan view of a prior art U-shaped spring used as a tool locking device; 
     FIG. 4 is a cross section view of an exemplary mastic supply tool which may be used in combination with the tool of FIG. 2; 
     FIG. 5 is a fragment of the tool of FIG. 2 with the inventive locking mechanism in a tool locking position; and 
     FIG. 6 is the same tool fragment that is shown in FIG. 5, but with the inventive mechanism in a tool unlocking position. 
    
    
     DESCRIPTION OF THE INVENTION 
     FIG. 1 shows two large sheets of drywall 20, 22 which meet and abut at and are joined to provide an inside corner A. Most of the time, the angle A is a nominal 90°; however, buildings are not that precisely built and so there may, within reason, be a considerable variation in angle A. The object of the corner finisher tool 26 is to apply a tape 28 which covers the crack 24 between the drywall sheets and to place mastic in the corner to protect the tape and to give a plaster-like surface. Each of the longitudinal halves of the tape which are secured against walls 20, 22 should fit smoothly and cling to the wall without any wrinkles or buckles. The fold 30 should fit smoothly over the crack 24, without either spanning or fitting into the crack. 
     Therefore, to smooth both the tape and the mastic, corner finisher tool 26 has two converging flat plates or surfaces 32, 34 which are set at a 90° angle with respect to each other in order to fit against the two wall surfaces 20, 22. The mastic (sometimes called &#34;mud&#34;) is applied over the tape 28 in order to strengthen the tape and to provide a plaster-like surface. To smooth the tape 28 and mastic, the handle 38 is manipulated to move tool 26 up or down the corner of the walls. The tool 26 should be able to tip and alter its posture somewhat relative to the handle 38 so that the plates 32, 34 always rest firmly against wall surfaces 20, 22 despite minor variations of the wall construction. 
     As shown in FIG. 4, there is a housing 36 that contains mastic which is pressed out and on to the wall as pressure is applied by a manually manipulated pole 38. Another tool might apply the mastic through a pressurized hose and a pipe (FIG. 2). Yet another mastic smoothing tool might not deliver any mastic, relying instead upon mastic which is manually applied to the drywall by a workman wielding a trowel. Depending upon conditions that are encountered at any time, the workman may want to use any or all of these tools, even on a single joint. To accommodate all of these needs, a quick disconnect coupler 40 is provided so that the workman can switch tools quickly and easily. 
     More particularly, FIG. 2 is an exploded view of a prior art corner finisher tool 26 which is adapted to use the inventive quick disconnect coupler, shown in greater detail in FIGS. 5, 6. FIG. 2 shows a pressurized hose and pipe 42 (sometimes called a &#34;bazooka&#34;) for supplying mastic via a ball 44 of a ball and socket joint forming the quick disconnect coupler 40 of FIG. 1. 
     The pressure in the hose and pipe may tend to blow the corner finisher off the ball 44. FIG. 4 shows another mastic applying tool comprising a box or housing 36 defining a cavity 54 for supplying a limited amount of mastic responsive to a manually applied pressure at socket 46. The workman might want to use the bazooka 42 to apply a first and heavy coat of mastic. He might want to use the tool of FIG. 4 to apply a second and medium coat of mastic. Finally, he might want to use only a pole terminating in a ball connector in order to smooth a thin coat applied by a hand trowel. 
     Alternative tools may be substituted for each other. More particularly, the ball 44 (FIG. 2) or ball 48 (FIG. 4) may be substituted for each other by fitting into a socket 50 (FIG. 2) in order to provide the quick disconnect coupler 40 so that any of these or other tools may be used. 
     The corner finisher 26 of FIGS. 1 and 2 is shown and explained in U.S. Pat. No. 4,767,297; therefore, it will not be explained in great detail at this point. In general, socket 50 and ball 44 together constitute the quick disconnect coupler 40 by screws 52, 53. Socket 52 is firmly attached to the back of a cast aluminum head 49 by screws 52, 53. A mastic delivery hole 52 (cavity 20 in U. S. Pat. 4,767,297) is formed in the apex of the angle between converging walls 32, 34. Socket 50 has a center hole 51 which confronts and communicates mastic with hole 52 in finisher 26. Socket 50 receives a ball 44 attached to a bazooka tool 42 which is used to apply the pressurized mastic through the aligned holes 51 in socket 50 and 52 in head 49. 
     Usually, a first of three coats of mastic, applied to the corner, is very heavy and is supplied through a bazooka or pressurized hose and pipe 42 and ball 44. Therefore, ball 44 is locked into socket 50 and thereby connected to the corner finisher. The second coat is thinner and is applied through the housing 36 of FIG. 4. Hence, to switch corner finisher 26 from bazooka 42 to housing 36, ball 44 is first removed from the socket 50 and then ball 48 is placed in socket 50. Then, a handle 38 (FIG. 1) is secured in socket 46 (FIG. 4) so that the joined combination of box or housing 36 and corner finisher tool 26 may be held against and moved over the wall. The handle 38 applies pressure on socket 46 and swings door 56 pivoted at 58 in order to push the mastic out of a hole 60 in ball 48 at the end of box or housing 36. After that, a coating of mastic is applied to the wall via opening 60 in the tool of FIG. 4. A very thin finishing coat may be applied by a trowel and smoothed down by a finishing pass of the tool. In this, case, no mastic passes through the corner finisher 26. Therefore, the ball 48 is removed from socket 50 and a solid metal ball on the end of a handle is placed in socket 50. 
     Heretofore, the quick disconnect coupler (FIG. 2) included a somewhat hairpin shaped, spring clip 62 (clip 56 in U.S. Pat. No. 4,767,297). The ball 44 or 48 was simply pushed against the spring clip 62 with enough &#34;brute force&#34; to spread the clip (as shown in FIG. 3) with the ball passing through the spread clip and into socket 50. Or, the ball was simply pulled from the spring clip 62. As the ball passes in either direction (connect or disconnect) through spring clip 62, this &#34;brute force&#34; causes the clip to spread from its normal configuration shown in FIG. 2 to the spread configuration shown in FIG. 3. Regardless of the direction in which the force is applied, after the ball has completed its pass through the spring clip 62, the resilience of clip 62 returns it to its normal configuration of FIG. 2. 
     For any of a number of reasons, the spring clip 62 may inadvertently release the ball which could result in an extensive amount of damage, as where a falling tool may clip a bath tub. For example, over a period of time, the spring clip 62 may lose at least some of its resilience. Sometimes the tool may strike the wall, or something else, with a sufficient force to cause the ball and socket to separate. 
     In order to provide a quick disconnect coupler which will not accidently release the ball 44 or 48 from socket 50, the spring clip 62 is replaced by a locking plate 64 (FIGS. 5, 6) which is slidingly attached to the back of the corner finisher 26. More particularly, locking plate 64 is held behind a pair of upper and lower guide plates 66, 68 and 70, 72 which guide and secure plate 64 to the corner finisher 26. These guide plates may be bolted to the back of the cast aluminum part 49; or, the cast part 49 may be made with slides 66, 68 and 70, 72 integrally formed therein during the casting. 
     The locking plate 64 has a dependant actuator tab 74 which may be pushed in direction B in order to raise the plate 64 against the bias of a coiled spring 76 or released so that it is restored under the spring bias. Coiled spring 76 is positioned between the top of locking plate 64 and a cap 78 (called a &#34;frame keeper 10&#34; in U.S. Pat. No. 4,767,297). The locking plate 64 has an upstanding tab 80 which receives the coiled spring 76 to help stabilize the spring position. When the tab 74 is pushed, spring 76 is compressed (Fig. 6). When tab 74 is released, the resilience of compressed spring 76 restores locking plate 64 to the normal position (FIG. 5). 
     A somewhat key hole shaped opening 82 is formed in locking plate 64 with a relatively large release opening 84 (FIG. 5) at the bottom and a relatively small capture opening 86 (FIG. 6) at the top. When the tab 74 is pushed in direction B in order to raise the locking pate 64 against the bias of spring 76, the large release opening 84 is in front of socket 50. Ball 44 or 48 may pass freely through the opening 84 and into the socket 50. When the tab 74 is released, the bias of coiled spring 76 pushes locking plate downwardly (i.e. direction C). The small capture opening 86 passes over neck 88 (FIG. 2) or neck 90 (FIG. 4) capturing the ball 44 or 48 behind it. With the locking plate 64 so positioned (FIG. 5), the ball 44 or 48 is captured. Hence, there is no easy way that the quick disconnect coupler 40 can accidently release the ball 44 or 48 from the socket 50. 
     Those who are skilled in the art will readily perceive how to modify the invention. Therefore, the appended claims are to be construed to cover all equivalent structures which fall within the true scope and spirit of the invention.