Sheet rock cutting tool

A sheet rock measuring and cutting device, comprising: a T-square arm for abutment with an edge of a piece of sheet rock; a base scale arm positioned within the T-square arm for selective sliding interengagement therewith; and a sliding scale arm positioned within the base scale arm for selective sliding interengagement therewith. The sliding scale arm includes a cutting tool engagement member for receipt and positioning of a cutting tool at a measured distance from the edge of the sheet rock.

FIELD OF THE INVENTION 
The present invention relates to a sheet rock cutting tool for cutting 
sheet rock or the like. More particularly, the present invention relates 
to a sheet rock cutting tool wherein a cutting tool is positioned within a 
sliding scale arm at a measured distance from a T-square arm allowing for 
measurement and cutting, or scoring, of a piece of sheet rock in a single 
motion. The sliding scale arm is positioned within a base scale arm for 
selective sliding interengagement therewith; a base scale arm is in turn 
positioned within the T-square arm for selective sliding interengagement 
therewith. 
BACKGROUND OF THE INVENTION 
Many tools have been made to facilitate the measurement and/or cutting or 
scoring of a piece of sheet rock to a desired size for use in the 
construction of building walls and ceilings. 
For example, U.S. Pat. No. 5,197,195 to Aikens describes a cutting guide 
apparatus having an elongate handle containing a magazine housing 
including a reel of flexible measuring tape extending through a guide 
plate that is adjacent a distal end of the handle. A collet member permits 
selective extension of the measuring tape and the forward distal end of 
the flexible measuring tape includes a support beam including a mount for 
a writing instrument and a cutting tool therein. However, the flexible 
nature of the measuring tape does not permit a rigid member to insure an 
accurate marking/scoring/cutting by a mounted writing instrument or 
cutting tool. This is especially relevant at greater extensions of the 
flexible tape from the handle and increases the difficulty of its use. 
U.S. Pat. No. 5,265,342 to Lang describes a drywall measuring and cutting 
tool having a guide riding the edge of a sheet of drywall and a rigid, 
graduated rod passing through an opening in the guide and normal thereto. 
A knife is fastened to the rod by a stem assembly and the stem assembly 
can be rotated for shallow or deep cuts. However, the idle rod length 
projects away from the knife through the guide which requires a minimum 
free space behind the sheet of drywall, especially for cuts closer to the 
guide. Additionally, the rod is selectively fixed within the guide by a 
downward pressure of the handle of the guide towards the rod which tends 
to lift the knife end away from the drywall and increases the difficulty 
in manipulating the device to cut or score the sheet of drywall. Also, 
since the depth of the score/cut is determined by rotation of the stem 
assembly, the user must exert a constant and consistent downward pressure 
on the handle of the stem assembly to ensure a consistent depth of 
scoring/cutting. This further complicates use of the device. 
U.S. Pat. No. 2,818,644 to Crawford describes a wallboard measuring and 
cutting device having a sliding stop member with a flat, rigid, elongated 
calibrated rod passing through an opening in the stop member and normal 
thereto. Secured to one end of the rod is a block member which extends 
transversely to the rod. The block member includes a cutting blade 
perpendicular to the rod and selectively positioned to score or cut a 
sheet of drywall or the like. The opposite end of the rod includes a 
depending stop block which prevents removal of the sliding stop member. In 
use, the sliding stop member is selectively positioned along the 
calibrated rod at a specified distance from the cutting blade as read by 
the markings on the rod and is fixed in position by a pivoting arm having 
a curved bottom which frictionally engages the rod. The sliding stop 
member projects below the plane of the bottom of the calibrated rod and 
includes an edge which abuts the edge of a sheet of drywall. The device is 
guided along the edge of the drywall scoring/cutting the drywall at the 
specified distance. However, as in Lang, the idle rod length projects away 
from the block member/cutting blade which requires a minimum free space 
behind the sheet of drywall, especially for cuts closer to the sliding 
stop member. 
U.S. Pat. No. 3,286,351 to McAlister describes a sheetrock scriber which 
scribes, or scores, a piece of sheetrock, or the like, at a predetermined 
distance so that the sheetrock can be accurately broken off to the desired 
size. The sheetrock scriber having a carriage riding over a piece of 
sheetrock on a set of tandem rollers on one end and a single roller 
positioned on a scriber head member at the other end of a ruler arm 
extending from the carriage. The tandem rollers are spaced and journaled 
on a vertically extending leg and are journaled on individual axles. The 
vertically extending leg has an edge with beveled lips angling outwardly 
to facilitate abutment of the leg with an edge of the sheetrock. The ruler 
arm may be suitably graduated to allow measured placement of a scriber 
blade within the scriber head member at the desired distance from the edge 
of the vertically extending leg. The scriber head member is selectively 
positioned along the ruler arm by squeezing of a lever member against the 
scriber head member to clamp the ruler arm at the desired distance. The 
scriber blade projects below the single roller at a predetermined fixed 
distance to ensure proper scribing of the sheetrock. 
However, similar to Lang and Crawford, the idle ruler arm length projects 
away from the vertically extending leg which requires a minimum free space 
behind the sheetrock, especially for cuts closer to the vertically 
extending leg. Further, the rollers upon which the carriage/ruler arm 
rides over the sheetrock are subject to binding upon embedding of pieces 
of scribed sheetrock and dust in their axles/sleeves produced during use 
of the device. This could lead to necessary periodic cleaning of the 
roller members and difficulty in the efficient use of the device due to 
difficult scribes and may lead to binding or jumping of the device 
creating nonlinear scribes and therefore nonlinear breaking of the 
sheetrock. 
U.S. Pat. No. 4,644,663 to Needs describes a measuring device to locate, 
dimension and mark the proper locations for the successive formations of 
score lines in a plurality of multi-sided conduits or ducts formed from 
planar sheets of duct board without having to reset the device each time a 
separate duct board is marked. The measuring device being in the form a 
T-square having a rigid, elongated body and a perpendicularly arranged 
head portion and further including a plurality of staggered, offset scales 
extending along the length of the body in adjacent, side-by-side and 
parallel relation to one another from the head portion towards a distal 
end. A plurality of scale indicators, preferably equal in number to the 
number of scales, are positioned to slide along the length of the body in 
aligned indicating relation with one of the plurality of scales. Each 
scale indicator includes a locking member to selectively lock each scale 
indicator relative to its respective scale. Each scale indicator further 
includes a marker member extending outwardly therefrom and positioned to 
allow markings to be made on the product being measured by the device by 
each scale indicator marker member as determined by the locked position of 
the scale indicator relative to the measurement indicia on its respective 
scale. The device is intended to allow for accurate multiple V-shaped 
scorings of successive duct boards so that each scored duct board may be 
folded upon itself along the score lines to form multiple, identical 
substantially rectangularly-shaped ducts or conduits that may then be 
affixed to each other end-to-end to create, most commonly, air 
conditioning ducts. Each V-shaped score line has a definite width which 
must be accounted for to allow proper placement of the next and successive 
score lines to allow formation of the selected sized duct. The scales are 
staggered a predetermined amount relative to each other to account for the 
V-shaped score line width. 
In use, the device is set so that the side-by-side scales are offset an 
appropriate amount for the size of the duct to be formed and the marker 
members are locked at the desired positions. Marks are made at each marker 
member at either end of the duct boards and a straight edge is used to 
connect the pairs of marks made by the device to indicate along the entire 
appropriate dimension of the duct board where the V-shaped score lines are 
to be cut by a separate tool. The Needs device is not designed to make 
continuous score lines to cuts but is instead designed to account for the 
width of the V-shaped score lines, to be subsequently produced by a 
separate tool, necessary to form rectangular-shaped ducts from the duct 
boards. Further, the device is not compact and is of a fixed length 
creating an unnecessarily bulky and unwieldy device for simple scoring or 
cutting of a sheet of material to a single desired width. 
U.S. Pat. No. 4,949,462 to Spencer describes a drywall cutting device that 
includes a channel-shaped sleeve for slidably mounted disposition on a 
stem of a T-square at predetermined selectable positions. A handle 
operated clamping device consisting of a screw inserted in a threaded hole 
in the sleeve that may be rotated so that the screw's distal end engages 
the stem of the T-square is provided to selectively position the sleeve on 
the stem. The sleeve further includes a knife holder within which a knife 
is positioned perpendicular to the stem for cutting a line perpendicular 
to the stem when the clamping device and the T-square are drawn together 
across a surface to be cut. The stem may include graduated indicia to 
establish the measured distance from the knife edge to the edge of the 
T-square engaging the edge of the sheet of the material to be cut. As with 
Needs, McAlister, Crawford, and Lang, the device is not compact but 
instead is of a fixed length creating an unnecessarily bulky and unwieldy 
device. 
U.S. Pat. No. 4,799,315 to Ziegler describes a knife support and cutting 
guide for a type of cutting tool commonly used to cut paperboard as a 
border for framing pictures. The device having a two piece clamp at the 
end of a curved arm for holding the cutting tool while the other end of 
the curved arm has a first circular member which mates with a 
corresponding second circular member on the end of an elongated rod to 
selectively maintain the curved arm at a predetermined rotational 
orientation relative to the elongated rod by the use of a screw, for 
example. One of two interchangeable, surface engaging guide members is 
releasably retained at a desired position along the length of the rod 
permitting the cutting tool to make either a circular or a straight cut in 
the paperboard with a beveled edge. The rotational adjustment of the two 
circular members permits alignment of the cutting tool edge when making 
circular cuts to eliminate blade drag. The elongated rod is selectively 
slidingly engaged to the surface engaging guide members through a hole 
therein to allow for selective adjustment of the distance from the cutting 
tool to the chosen surface engaging guide member. To make straight cuts, a 
flat edged surface engaging guide member is chosen to produce a T-square 
shaped device with the elongated rod perpendicularly attached to the flat 
edge member. The flat edge member abuts the edge of the material to be cut 
and the flat edge member and cutting tool is drawn along the edge of that 
material to cut the material at a predetermined distance from its edge. 
As with Needs, McAlister, Crawford, Lang, and Spencer, the Ziegler device 
is not compact but instead is of a fixed length creating an unnecessarily 
bulky and unwieldy device. Further, the device is of a relatively flimsy 
construction for cutting sheet rock over prolonged periods and is not 
provided with calibrated indicia to permit rapid and accurate measured 
scoring or cutting. None of the prior art patents disclose a compact sheet 
rock scoring/cutting device that is useful over the range of measured 
distances for common sheet rock. 
Accordingly, it is an object of this invention to provide a sheet rock 
cutting tool that is compact while extendible to allow cutting of standard 
sizes of sheet rock. 
Another object of the present invention is to provide a tool that permits 
measuring and scoring or cutting sheet rock in a single motion. 
Other objects will appear hereinafter. 
SUMMARY OF THE INVENTION 
It has now been discovered that the above and other objects of the present 
invention may be accomplished in the following manner. Specifically, the 
present invention provides a T-square arm for abutment with an edge of a 
piece of sheet rock; a base scale arm positioned within the T-square arm 
for selective sliding interengagement therewith; and a sliding scale arm 
positioned within the base scale arm for selective interengagement 
therewith. The sliding scale arm includes a cutting tool engagement member 
for receipt and positioning of a cutting tool at a measured distance from 
the T-square arm such that a piece of sheet rock may be measured and cut 
or scored in one motion. 
In the preferred embodiment, the T-square arm includes a body having 
upwardly curved sides and an arm perpendicular to the body. The arm has a 
leading edge for abutment with the edge of the piece of sheet rock. The 
base scale arm has graduated indicia thereon increasing from left to right 
from twelve to twenty-four inches and further has upwardly curved sides. 
The base scale arm is positioned within the T-square body and retained by 
the upwardly curved T-square arm body sides for selective sliding 
interengagement therewith. The sliding scale arm has graduated indicia 
thereon increasing from right to left from zero inches to twelve inches 
and is positioned within the upwardly curved base scale arm sides for 
selective sliding interengagement therewith. 
A first threaded opening pierces the body of the T-square arm and is sized 
to receive a first thumb screw and is positioned such that threading the 
first thumb screw into the first threaded opening causes the end of the 
first thumb screw to engage the base scale arm to selectively fix the base 
scale arm within the T-square arm body. Two projections are positioned on 
the left side of the sliding scale arm a predetermined distance apart. A 
generally square shaped plate, sized to fit within the base scale arm, 
rests on the sliding scale arm between the projections. The plate is 
pierced by a second threaded opening centered therein and is positioned 
and sized to receive a second thumb screw such that threading the second 
thumb screw into the second threaded opening causes the end of the second 
thumb screw to engage the sliding scale arm and press the plate upwardly 
against a portion of the base scale arm sides to selectively fix the 
sliding scale arm within the base scale arm. 
The left underside of the base scale arm includes a downwardly projecting 
tab and the left side of the body of the T-square arm includes a cut-out 
sized for receipt of the projecting tab wherein engagement of the tab with 
the cut-out limits the left-most positioning of the T-square arm on the 
base scale arm. A stop plate is fixedly mounted on the right end of the 
sliding scale arm and is sized to abut the right end of the base scale arm 
wherein abutment of the stop plate with the right end of the base scale 
arm limits the left-most positioning of the sliding scale arm within the 
base scale arm. 
A first diamond shaped opening piercing the right end of the sliding scale 
arm and a second diamond shaped opening piercing the stop plate are in 
alignment. These first and second diamond shaped openings are sized for 
receipt of a cutting blade of the cutting tool at a measured distance from 
the T-square arm such that when the T-square arm is fixed at its left-most 
position on the base scale arm, and the sliding scale arm is fixed at its 
left-most position within the base scale arm, the distance from the 
leading edge to the cutting edge of the cutting blade is twelve inches.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the drawings, and specifically in FIGS. 1 and 2, a sheet rock 
cutting tool made in accordance with the present invention, generally 
indicated as 10, includes: T-square arm 15 having leading edge 67 for 
abutment with an edge 16 of a piece of sheet rock 18; base scale arm 11 
positioned within T-square arm 15 for selective sliding interengagement 
therewith; and sliding scale arm 13 positioned within base scale arm 11 
for selective sliding interengagement therewith. Sliding scale arm 13 
includes cutting tool engagement member 14 for receipt and positioning of 
a cutting tool 20 held by a user 22 at a measured distance 24 from leading 
edge and sheet rock edge 67 and 16, respectively. Device 10 may be 
manufactured from metal, such as aluminum, although it is preferably made 
of plastic or a similar material which reduces manufacturing costs. 
In the preferred embodiment, T-square arm 15 includes channel shaped body 
32, having curved retaining sides 25, and arm 31 perpendicular to body 32. 
Each end of arm 31 includes beveled lips 33 angling outwardly to 
facilitate abutment of leading edge 67 of arm 31 with edge 16 of sheet 
rock 18. Body 32 includes first threaded opening 28 piercing one of curved 
retaining sides 25 within which first thumb screw 29 engages. Body 32 
further includes cut-out 27 centered on its lower edge opposite arm 31. 
Base scale arm 11 includes graduated indicia 17 increasing from left to 
right and preferably from twelve inches to twenty-four inches at its left 
edge. Base scale arm 11 is channel shaped with curved retaining sides 23 
sized to slidingly engage within curved retaining sides 25 of T-square arm 
15. Once base scale arm 11 is slidingly engaged within body 32 of T-square 
arm 15, it may be selectively and reversibly fixed within body 32 by, for 
example, engaging first thumb screw 29 into first threaded opening 28 such 
that the distal end of first thumb screw 29 frictionally engages a portion 
of a base scale arm curved retaining side 23 fixing base scale arm 11 
relative to body 32. As best shown in the cut-away portions of FIGS. 3 and 
4, the bottom center of the left end of base scale arm 11 includes 
downwardly projecting tab 21 which is received within cut-out 27 to limit 
the left-most position of T-square arm 15 relative to base scale arm 11. 
Sliding scale arm 13 is flat with a generally rectangular cross-section and 
includes graduated indicia 19 increasing from right to left and preferably 
from zero to twelve inches proximate set plate 51. Sliding scale arm 13 is 
sized to slidingly engage within curved retaining body sides 23 of base 
scale arm 11. The right end of sliding scale arm 13 includes a first 
diamond shaped opening 41. Channel shaped stop plate 35, with curved 
retaining sides 47, is attached to the right end of sliding scale arm 13 
by, for example, screws 45 through threaded openings (not shown) in stop 
plate 35 and threaded openings (not shown) in the right end of sliding 
scale arm 13. Stop plate 35 is sized such that the left side of its 
retaining sides 47 abut the right side of base scale arm retaining sides 
23 to limit the left-most position of sliding scale arm 13 relative to 
base scale arm 11. 
Stop plate 35 includes a second diamond shaped opening 37 in alignment with 
first diamond shaped opening 41 in sliding scale arm 13. Cutting tool 
engagement member 14 includes first and second diamond shaped openings 41, 
37 which are sized for receipt of a cutting blade of cutting tool 20 in 
the upper apex 38 and lower apex 40 of aligned first and second diamond 
shaped openings 41, 37. Other known devices may be used to retain cutting 
tool 20 to, for example, eliminate the need for manual positioning and 
holding of cutting tool 20. As discussed below, the reading of the 
appropriate graduated indicia 17, 19 at left edge 26 of sliding scale arm 
13 and measuring line 69 at the right edge of curved sides 25, 
respectively, will determine measured distance 24 from the cutting blade 
of cutting tool 20 to leading edge 67 and sheet rock edge 16, 
respectively, to allow accurate measuring and cutting of sheet rock 18 in 
one motion. 
It is noted that reading scale 19 of sliding scale arm 13 at the right hand 
edge of the upper curved side 25 of T-square arm body 32, or measuring 
line 69 formed between the right hand edges of curved sides 25 of T-square 
arm body 32, greatly facilitates accurate and precise measurement of 
desired distance 24 from the leading edge 67 of T-square arm 15 to the 
center of first and second diamond shaped openings 41, 37. This avoids 
having to read scale 19 at leading edge 67 of T-square arm 15 or edge 16 
of sheet rock 18 which are below and further apart from scale 19. 
Sliding scale arm 13 includes two spaced apart, upwardly projecting 
projections 49 on its left end opposite stop plate 35. Generally square 
shaped set plate 51 is sized to snugly fit between projections 49 and 
within curved retaining sides 23 of base scale arm 11 when sliding scale 
arm 13 is slidingly engaged in base scale arm 11. Reinforcing plate 53 is 
generally rectangularly shaped and is diagonally fixed to the center of 
set plate 51 by tack welding, for example. Second threaded opening 55 
pierces the approximate center of reinforcing plate 53 and set plate 51 
within which second thumb screw 61 engages. Once sliding scale arm 13 is 
slidingly engaged within base scale arm 11, it may be selectively and 
reversibly fixed within base scale arm 11 by, for example, engaging second 
thumb screw 61 into second threaded opening 55 such that the distal end of 
second thumb screw 61 abuts a portion of the upper surface of sliding 
scale arm 13, pushing set plate 51 upwardly against the inside of a 
portion of curved retaining sides 23 frictionally fixing sliding scale arm 
13 relative to base scale arm 11. 
Alternatively, set plate 51 may be permanently attached to sliding scale 
arm 13 by, for example, rivets (not shown) so that set plate 51 does not 
separate from sliding scale arm 13 during use or disassembly of sheet rock 
cutting tool 10 thus eliminating the risk of loss of set plate 51. This 
would eliminate the need for projections 49. Attachment of set plate 51 in 
such a manner would still allow set plate 51 vertical play to permit 
frictional engagement and disengagement of set plate 51 against curved 
retaining sides 23 when second thumb screw 61 is turned. 
Of course it is possible for sliding scale arm 13 to engage base scale arm 
11 by other methods such as, for example, including a U-shaped channel 
(not shown) in the right end of base scale arm 11 extending proximate the 
left end of base scale arm 11. Instead of set plate 51 et al, sliding 
scale arm 13 may include an opening at its left end within which a thumb 
screw, for example, is freely inserted and which also freely fits within 
the U-shaped channel of base scale arm 11. A nut may be then engaged at 
the distal end of the thumb screw and which is flush with the bottom of 
base scale 11 to avoid contact with sheet rock 18 at selected measuring or 
cutting distances. Sliding scale arm 13 is then selectively fixed relative 
to base scale arm 11 by turning the thumb screw to frictionally engage 
sliding scale arm 13 and base scale arm 11. 
Use of sheet rock cutting tool 10 of the preferred embodiment of the 
present invention is as follows. In any case, leading edge 67 of T-square 
arm 15 is placed flush to abut an edge 16 of sheet rock 18 to be measured 
and/or cut. For measuring and cutting from more than twelve inches to 
twenty-four inches of the sheet rock 18 as shown in FIG. 3, T-square arm 
15 is positioned and fixed at its left-most limit relative to base scale 
arm 11 by engaging tab 21 in cut-out 27 and engaging first thumb screw 
into first threaded opening 28. Sliding scale arm 13 is positioned 
relative to base scale arm 11 at the desired distance to be cut at 13' and 
second thumb screw 61 is engaged into second threaded opening 55 fixing 
sliding scale arm 13. The desired distance 24 is read on the base scale 
arm indicia 17 at the left edge 26' of sliding scale arm 13' which is the 
distance from the center of first and second diamond shaped openings 41, 
37 to leading edge 67 and thus the length of the desired cut. Cutting tool 
20, such as a utility knife, is inserted and held in cutting tool 
engagement member 14 such that the blade of utility knife 20 is held 
between the upper apex 38 and lower apex 40 and inserted to make the 
desired depth of cut. Sheet rock cutting tool 10 is then guided along edge 
16 of sheet rock 18 maintaining the flush abutment of leading edge 67 of 
T-square arm 15 against edge 16 while utility knife 20 cuts or scores 
sheet rock 18 at the desired distance 24 from edge 16. 
For measuring and cutting from twelve inches to just over zero inches as 
shown in FIG. 4, sliding scale arm 13 is positioned and fixed at its 
left-most position relative to base scale arm 11 by engaging second thumb 
screw 61 into second threaded opening 55. Base scale arm 11, with sliding 
scale arm 13 fixed thereto, is positioned relative to T-square arm 15 at 
the desired distance 24 to be cut at 15' and first thumb screw 29 is 
engaged into first threaded opening 28 fixing base scale arm 11. The 
position of the right hand edge of the upper curved side 25 of T-square 
arm body 32, or measuring line 69', relative to sliding scale arm 
graduated indicia 19 gives the distance from the center of first and 
second diamond shaped openings 41, 37 to leading edge 67. Cutting tool 20, 
such as a utility knife, is inserted and held in cutting tool engagement 
member 14 such that the blade of utility knife 20 is held between the 
upper apex 38 and lower apex 40 and inserted to make the desired depth of 
cut. Sheet rock cutting tool 10 is then guided along edge 16 of sheet rock 
18 maintaining the flush abutment of leading edge 67 of T-square arm 15 
against edge 16 while utility knife 20 cuts or scores sheet rock 18 at the 
desired distance 24 from edge 16. 
If it is desired to only measure or mark sheet rock 18, a pencil or other 
like marking device, not shown, may be inserted into an apex 38, 40 
depending upon which direction sheet rock cutting tool 10 is guided along 
edge 16. For example if sheet rock cutting tool 10 is to be guided 
downwardly along sheet rock 18, a pencil is placed in upper apex 38. The 
motion of sheet rock cutting tool 10 downwardly tends to maintain 
engagement of the pencil in upper apex 38. Similarly, the pencil is placed 
in lower apex 40 if sheet rock cutting tool 10 is to be guided upwardly 
along sheet rock 18. 
While particular embodiments of the present invention have been illustrated 
and described, it is not intended to limit the invention, except as 
defined by the following claims.