Sander having a planar surface convertible to a right angular surface

A hand operateable sander having a flat sanding block for sanding flat surfaces and which automatically pivots into a "V" shape for sanding outside corners and bullnose surfaces.

This invention relates to hand tools and in particular to a drywall sander 
with a flat sanding surface that automatically converts into a bullnose 
sander for the finishing sanding of walls, ceilings and bullnose surfaces. 
SUMMARY OF THE INVENTION 
One of the final steps in building construction is the installation of 
interior walls which is usually accomplished by installing large wall 
panels between the floor and ceiling. These panels are generally a paper 
covered plaster sheet of standard width and are known in the trade as 
drywall. The wall or ceiling is formed by abutting these drywall panels 
and nailing them to the studs or joists with the nails slightly 
countersunk. Then the countersunk nail heads and the abutting junctures of 
the panels are taped with a heavy paper tape cemented with a drywall 
cement that eventually dries with the appearance and texture of plaster. 
Before a wall and ceiling is painted, it must be sanded smooth to remove 
the irregularities, such as the roughness of dried drywall cement. For 
flat surfaced walls, a flat sanding block is adequate, and for high 
ceilings an extension handle is needed such as described by Helling in 
Pat. No. 4,663,796. But for outside corners and bullnose surfaces, it was 
necessary for the finish sander to hand sand or improvise a special 
sander. The sander described herein provides a flat block for sanding flat 
surfaces and automatically bands to sand bullnose surfaces. 
Briefly described, the sander of the invention is comprised of a flexible 
rubberlike sanding pad to which appropriate sand paper is attached. The 
sanding pad is secured to two elongated, parallel members which normally 
provide a flat surface but which can be pivoted inward to form a "V" 
shaped sanding block for sanding outside corners or bullnose surfaces. The 
two parallel members are pivoted to a lateral shaft to which a handle is 
attached.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The sander of the invention may be used on an extension handle as a flat 
sanding block for sanding flat surfaces, or folder into an inverted "V" 
for sanding outside corners or bullnose surfaces. As shown in FIG. 1 a 
sheet of sanding material, such as sandpaper 10, covers the bottom surface 
of a substantially square, flat, flexible, rubberlike pad 12, about 
one-quarter inch thick, that is cemented to the bottom surfaces of two 
spaced, parallel, elongated elements 14, 16. The sandpaper 10 is secured 
by clamps 18, 20 clamping the sandpaper 10 to the top surfaces of elongate 
elements 14, 16. The sandpaper clamps 18, 20 have been omitted from the 
drawings of FIGS. 2 and 3 for clarity. 
The elongated elements 14, 16 are formed of a rigid metal about one eighth 
inch thick and have flat bottom surfaces, a length substantially equal to 
the overall length of the sander, as shown in FIG. 2, and each has a width 
substantially equal to one-third the overall width of the sander, as seen 
in FIG. 1. The elongated elements 14, 16 are parallel and separated by a 
space equal to one-third the sander width. 
On the top surface near each end of each of the two elongated elements 14, 
16 are one inch risers 22, 24, 26, 28 which contain parallel pivot pins 29 
which pivotally connect the members 14, 16 to frames 30 and 32. Thus, the 
frame 30 is pivotally coupled to the elongated element 14 by coaxial pivot 
pins extending through the risers 22 and 26, as shown in FIG. 2, and 
similarly, the frame 32 is pivotally coupled to the element 16 by coaxial 
pivot pins through the risers 24 and 28, as best shown in FIG. 3. 
The two frames 30, 32 each contain second parallel pivot pins 33 near the 
frame centers, and also have limiting features which will be subsequently 
described. The second pivot pins 33 pivotally connect the center portion 
of the two frames 30, 32 to identical shaft terminal blocks 34, 36 at the 
ends of a central lateral shaft 38 which has a centrally positioned socket 
40 for the attachment of a short handle or an extension handle. Shaft 38 
may be a straight shaft but is preferably arched, as shown, to avoid any 
interference with the flexible pad 12 when the pad is bent as shown in 
FIG. 4. 
The shaft terminal blocks 34, 36 are also pivotally connected to the 
lateral shaft 38 by bolt 39 to permit the handle socket 40 to freely swing 
back and forward. The terminal blocks are identical, each is rectangular 
in shape, as best shown in FIG. 4, with small rectangular side extensions 
42 extending to the sides from the top, producing a top plan view of the 
terminal block to appear as a "T", as seen in FIG. 3. These extensions 42 
cooperate with the top flat surface of frames 30, 32 to limit the pivotal 
action of the frames to a downward movement. Additionally, the flat inner 
surfaces 44, 46 of the frames 30, 32, which are normally in contact with 
the flat exterior faces of the shaft terminal blocks 34, 36, will prevent 
pivotal movement except the outward pivoting of the frames 30, 32 on the 
pivots 29, as seen in FIG. 4. Thus, the relative pivotal motion between 
the terminal blocks 34, 36 and the frames 30, 32 is limited to only one 
direction from the normal planar sander of FIG. 1. 
When sanding a flat surface, the sander is pressed against the surface and 
the flat lower surfaces of the elements 14, 16 will be forced into the 
planar shape of FIG. 1. When sanding anything that causes the flat lower 
surfaces of elements to turn in toward each other, such as a bullnose edge 
a slight pressure on the handle will urge the flexible sanding pad 12 to 
bend as in FIG. 4. This bending toward a right angle by the pad 12 causes 
the pivots 29 on the risers 22, 24 and the bottom portions of the 
elongated frames 30, 32 to move outward. The frames are attached to the 
handle shaft 38 by the pivot pins 33 which couple the frames to the shaft 
terminal blocks 34,36.