Corner radius tool

A corner radius tool is provided for use in applying plaster material or the like to an inside corner joint between drywall panels to form a controlled and smoothly radiused surface. The tool includes a tool head in the form of a forwardly open resilient cup carried at a forward end of a tool handle, wherein the cup is adapted to support a quantity of the plaster material as the handle is manipulated to press and spread the plaster material along the inside corner joint. The resilient cup deforms upon engagement with the drywall panels at the corner joint to spread the plaster material with a desired and smoothly radiused surface. The specific radiused geometry of the plaster material surface is variably controlled by varying the orientation of and manual pressure applied to the resilient cup.

BACKGROUND OF THE INVENTION 
This invention relates generally to tools and related methods of use for 
applying plaster material or the like to an inside corner joint between 
adjacent drywall panels in a building. More specifically, this invention 
relates to an improved and easy-to-use corner radius tool for spreading 
plaster material along an inside corner joint with a smoothly radiused and 
variably selected surface geometry. 
Drywall panels of plaster-board material or the like are used extensively 
in residential and commercial construction projects to form interior walls 
within a building structure. In accordance with common construction 
techniques, the drywall panels are securely mounted onto frame components 
such as wall studs. Thereafter, joints formed between adjacent drywall 
panels are taped and filled with plaster material or the like to form a 
desired smooth and substantially uninterrupted wall surface. 
The process of taping and filling exposed joints between adjacent drywall 
panels involves substantial manual labor and considerable skill to provide 
the desired smooth and attractive wall surface. In this regard, particular 
difficulties are encountered in filling an inside angle corner joint. More 
specifically, plaster material is pressed into and spread along the inside 
corner joint in an effort to form a smoothly radiused corner surface of 
substantially continuous cross-sectional geometry for the entire length of 
the corner joint. Variations in a radiused inside corner, involving 
fluctuations in sharpness of the corner contour, can be particularly 
unsightly. 
In the past, various manual tools have been provided for use by 
construction workers in the taping and filling of joints between drywall 
panels. Some of these tools have been specially adapted for applying 
plaster material to an inside corner joint, and in a manner providing a 
substantially uniform radiused surface at the corner joint. Such tools, 
however, have included rigid tool heads for spreading the plaster material 
with a fixed surface geometry, within an inside corner of fixed angular 
shape, for example, a ninety degree corner. Prior corner radius tools have 
not provided the ability to selectively vary the geometry of a smoothly 
radiused plaster material surface at an inside corner joint, nor have such 
prior tools been capable of forming a smoothly radiused surface on an 
inside corner joint formed at an angle other than ninety degrees. 
The present invention overcomes the problems and disadvantages encountered 
in the prior art, by providing an improved corner radius tool for applying 
plaster material to an inside corner joint between adjacent drywall 
panels, wherein a smoothly radiused corner surface of variably selected 
geometry can be formed quickly and easily at an inside corner of virtually 
any angle. 
SUMMARY OF THE INVENTION 
In accordance with the invention, a corner radius tool is provided for 
applying plaster material or the like to an inside corner joint between 
adjacent drywall panels in a building structure. The improved corner 
radius tool includes a resilient tool head for supporting a quantity of 
the plaster material as the tool head is pressed into and moved along an 
inside corner joint. The tool head deforms against the drywall panels at 
the corner joint and is shaped when deformed to define a trailing edge of 
selected geometry for spreading the plaster material with a smoothly 
radiused surface as the tool head is drawn along the corner joint. The 
specific geometry of the radiused surface is variably selected by the 
orientation of the tool head relative to the corner joint and manual 
pressure applied to the tool head. By drawing the tool head along the 
corner joint at substantially constant orientation and pressure, a 
smoothly radiused corner surface of uniform cross-sectional shape is 
formed. 
In accordance with the preferred form of the invention, the improved corner 
radius tool comprises a manually grasped handle having a tool shank 
projecting forwardly therefrom. The tool head comprises a resilient cup 
mounted at a forward end of the tool shank, wherein the resilient cup 
defines a forwardly presented concave cup interior for receiving a 
quantity of the plaster material or the like. In the preferred form, the 
forward end of the tool shank includes a bend for supporting the resilient 
cup at an angle of about 30.degree. to a longitudinal axis of the tool 
handle. In addition, diametric cup sizes on the order of about two to four 
inches are preferred. 
In use, the corner radius tool can be used to scoop a quantity of the 
plaster material into the concave resilient cup. The plaster material is 
then pressed into an inside corner joint, and drawn along the joint in 
either direction while maintaining the resilient cup at a substantially 
constant orientation and under substantially constant manual pressure. 
Other features and advantages of the invention will become more apparent 
from the following detailed description, taken in conjunction with the 
accompanying drawings which illustrate, by way of example, the principles 
of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown on the exemplary drawings, a corner radius tool referred to 
generally by the reference numeral 10 is provided for filling an inside 
corner joint 12 with a plaster material 14 or the like to define a 
smoothly radiused corner surface, as viewed in FIG. 1. The inside corner 
joint 12 is formed at the intersection of adjacent drywall panels 16. 
Appropriate orientation and manipulation of the corner radius tool 10 
provides easily varied selection of the geometry of the radius corner 
surface. Moreover, the tool 10 may be used for filling inside corner 
joints of virtually any angle. 
FIG. 1 illustrates use of the corner radius tool 10 of the present 
invention for filling a vertical inside corner joint 12 having an angle of 
about 90.degree. (FIG. 2) and extending between the ceiling 18 and floor 
(not shown) of a room within a building structure. In this regard, the 
drywall panels 16 are commonly used to define interior walls of a 
residential or commercial building structure. In the construction process, 
the inside corner joint 12 is filled with the plaster material 14 to form 
an attractive and smoothly radiused corner surface which blends smoothly 
and substantially continuously with the broad surfaces of the drywall 
panels 16. Additional inside corner joints, such as those shown in FIG. 1 
to extend along the tops of the panels 16 and the ceiling panel 18 are 
also filled with plaster material, preferably with the use of the improved 
corner radius tool of the present invention. 
As shown in FIG. 3, the tool 10 comprises a handle 20 adapted for easy 
manual grasping by a workman 22 (FIG. 1). A narrow tool shank 24 protrudes 
forwardly from the handle 20, and terminates in a forward tip 26 bent or 
angularly set with respect to a longitudinal axis of the handle 24. The 
shank tip 26 is received into a rearwardly open mounting boss 28 formed on 
a tool head 30. As shown, the tool head 30 comprises a resilient cup 
defining a forwardly open, generally concave cup interior 31. The 
cross-sectional geometry of the resilient cup may have a parabolic or 
hemispherical configuration. The outer diametric size of the resilient cup 
is preferably within the range of from about two inches to four inches. In 
typical use, more than one coat of the plaster material is applied to the 
inside corner joint, with a first coat being applied with a tool head 
having a diametric size of about two and one-half inches. A second or 
finish coat of the plaster material is then applied using a different tool 
head having a larger diameter of about three to three and one-half inches. 
In both instances, a tool head durometer on the order of about forty to 
fifty five Shore A hardness is preferred. 
The plaster material 14 is normally mixed with water and a supply thereof 
is carried by the workman 22 in a hand-held tray 32. The tool 10 is easily 
maneuvered to scoop a quantity of the plaster material 14 into the concave 
interior 31 of the resilient cup 30. The tool head carrying the plaster 
material 14 is then pressed into the selected inside corner joint 12, 
while holding the resilient cup at a selected orientation and pressing 
toward the corner joint with a selected manual pressure. The resilient cup 
30 deforms against the drywall panels 16 to reshape a trailing edge of the 
cup into a smoothly radiused surface for spreading the plaster material 
along the corner joint. FIGS. 1 and 2 show downward displacement of the 
tool 10 along the corner joint to spread the plaster material, whereas 
FIGS. 5 and 6 show upward displacement of the tool. In either case, a 
smoothly radiused corner surface of selected geometry, according to tool 
head orientation and manual pressure, is achieved. In general terms, 
increased manual pressure applied to the tool head causes greater 
deformation of the cup 30 and thus forms the plaster material with a 
sharper corner line. 
FIG. 7 shows the corner radius tool 10 applied to an inside corner joint 36 
of different angle, namely, an angle of about 120.degree.. Once again, 
manual pressure applied to the tool head in a direction toward the corner, 
in combination with tool head orientation, provides a smoothly contoured 
and highly uniform radiused surface geometry as the tool is drawn along 
the corner joint to spread the plaster material. 
FIG. 8 shows one alternative embodiment of the invention, wherein a 
modified handle 40 is mounted on the tool shank 24. The modified handle 40 
has a rectangular cross-sectional geometry, whereby planar surfaces of the 
handle can be manually perceived by the workman to assist in maintaining a 
constant tool head orientation relative to a corner joint, as the 
implement is drawn along the corner joint to apply the plaster material. 
The improved corner radius tool 10 of the present invention thus provides a 
versatile yet easy-to-use implement for applying and spreading plaster 
material with a smoothly radiused and substantially constant geometry 
along an inside corner joint of a building wall. The tool 10 can be used 
to form smoothly radiused corner joint surfaces at inside corners of 
different angles, and/or with different corner joint configurations, in 
accordance with the manner and orientation of tool use. Importantly, 
uniform and attractive corner joint surfaces can be formed quickly and 
easily, and without requiring extensive workman skill or training. 
A variety of modifications and improvements to the corner radius tool of 
the present invention will be apparent to persons skilled in the art. 
Accordingly, no limitation on the invention is intended by way of the 
foregoing description and accompanying drawings, except as set forth in 
the appended claims.