Combination square, level and plumbing tool

A carpenter's square having a first and second leg at right angles to each other, and a third leg extending between the first and second legs. A magnetic strip on the first leg for attaching the tool to a metallic surface to be plumbed. A first notch in the third leg a first distance from the first leg and a second notch in the third leg a second distance from the first leg so that a plumb string can be threaded through the first and second notches and thereby held in place to support a plumb bob to allow a plumb reading to be taken without the need for manually supporting the plumb bob.

TECHNICAL FIELD 
This invention relates to measuring instruments and, more particularly, to 
a tool for leveling, squaring and plumbing any individual or 
interconnected objects of any shape for use by builders, carpenters, 
plumbers, machinists and the like. 
BACKGROUND ART 
The typical carpenter's square has been well known for many years and is a 
very necessary and useful tool in most fields of construction. Hardly 
anyone, whether a professional carpenter or craftsman, or mere amateur 
do-it-yourself home builder, has ever done any woodworking without having 
had to employ a square at one time or another. The square is the only 
convenient tool for assuring that two pieces of material have been fitted 
together exactly perpendicularly to each other, or that a single piece of 
material has adjacent edges which meet at a right angle. As is well known 
in many forms of professional or home workshop construction, it is most 
critical that complementary pieces of material fit together at a right 
angle, or that individual pieces have adjacent edges which meet at a right 
angle, in order for the finished product to be properly constructed in 
terms of rigidity, strength and aesthetic appearance. Tight tolerances are 
the rule, rather than the exception when dealing with this kind of work. 
Although the basic configuration of the carpenter's square has remained 
unchanged since the square was first developed, many improvements have 
been made which have substantially increased the efficient utilization of 
the square, as a result of which many different types of squares exist 
today. For example, the professional carpenter's square is still nothing 
more than a single piece of metal formed in the shape of an "L", that is, 
two legs joined to each other at a 90.degree. angle, each leg having 
markings thereon to indicate increments of linear measurement. Typically, 
the legs of this type of square are unequal and between 1 and 2 feet long 
since the square is used where the pieces of material have large 
dimensions, such as in the construction of a house. A smaller, more 
portable square, suitable for carrying on a tool belt and commonly known 
as a "speed square", is favored by many craftsmen. 
It is well known that carpenter's and other skilled workmen prefer to carry 
and use a minimum number of tools. Since a carpenter's square is an 
essential tool, numerous attempts have been made to improve the tool, 
often by combining the square with other tools or by adding features to 
the square. U.S. Pat. No. 3,499,225 to Darrah, for example, provides a 
2-piece hinged square with a horizontal level built into the tool. The 
tool includes a substantially V-shaped portion for fitting closely with a 
pipe or other member of circular cross-section, with magnets for attaching 
the tool to the pipe. The tool is designed primarily for ironworking, 
however, and does not address the recurring carpenter's problem of using a 
plumb bob to check corners which have been squared using the tool itself. 
U.S. Pat. No. 3,826,013 to Baher combines level, square, and plumb 
functions in one tool. However, Baher achieves its plumb readings 
indirectly by reading a horizontal bubble level held on an arm at right 
angles to the surface being plumbed. Such a reading would be likely to 
produce inaccuracies over distances greater than a few feet, when compared 
to equivalent plumb readings obtained by use of a plumb bob. Various other 
inventions have combined levels with squares, either as a way to achieve a 
plumb reading, or simply to add a level function, or as a combination of 
both. U.S. Pat. No. 4,503,624 to Whiteford combines a level with a square, 
with the intent of achieving a plumb reading. However, Whiteford suffers 
from the same inaccuracy drawbacks as Baher. U.S. Pat. No. 5,253,426 to 
Mosbrucker is similar in concept to Whiteford and Baher, and suffers from 
the same inaccuracy drawback. 
U.S. Pat. No. 5,269,066 to Walters illustrates an attempt to solve the 
accuracy problems of Whiteford, Baher, and Mosbrucker. Walters utilizes a 
square having full-length level bubbles contained in its legs. By 
combining full-length bubbles with long legs--the square of Walters' FIG. 
1 is 16.times.24 inches--Walters is presumably able to provide much more 
accurate plumb readings. However the Walters square is not a convenient 
size for a carpenter to carry on his tool belt. Moreover, it is still not 
certain that the plumb readings of Walters would be as accurate as those 
obtained using a conventional plumb bob. A further attempt to solve the 
above-mentioned accuracy problems may be found in U.S. Pat. No. 5,239,761 
to Wu, et al. Wu combines a square with an actual built-in plumb bob to 
allow for accurate plumb readings. However, the tool of Wu suffers from 
the drawback of not providing a no-hands means for fixing the plumb bob in 
place. Therefore, taking plumb bob readings remains a two-man job with the 
Wu tool. In an attempt to solve this problem, magnets have been used to 
free the hands of the user of various tools. For example, U.S. Pat. No. 
4,593,475 to Mayes provides a level with magnetic support. 
Despite all the attempts to improve on conventional squares by adding 
levels and plumb reading capabilities, there still remains a need for a 
convenient, highly portable tool which can accurately perform all the 
squaring, levelling, and plumb-reading functions which are repeatedly 
encountered in a variety of carpentry and other tasks. In addition, it 
would be ideal if such a tool were operable by a single workman. A tool 
which could accomplish the foregoing would take the place of several 
tools, and would allow a single workman to perform tasks which normally 
require at least two workmen to perform. 
DISCLOSURE OF THE INVENTION 
In accordance with this invention a combination tool for squaring, 
leveling, and determining plumb is provided. The tool includes a 
carpenter's square having a first and a second leg at right angles to one 
another, and a third leg extending between the first and second legs. A 
magnetic strip of sufficient strength to magnetically support the tool is 
provided along the first leg. optionally, a second magnetic strip could 
also be provided along the second leg. 
A notch is located in the third leg, a pre-determined distance from the 
outer surface of the magnetic strip. When the tool is attached to a metal 
surface, the notch is therefore also a pre-determined distance from that 
metal surface. A second notch is also provided in the third leg. 
In operation, the tool is first magnetically attached to a metal surface, 
typically the surface to be plumbed. A plumb bob string is then threaded 
through the first notch and also through the second notch. Typically, the 
plumb bob string will have a string reel at one end and a plumb bob at the 
other. When the string has been threaded as described, the plumb bob will 
be supported by the tool without the user having to manually support the 
plumb bob or tool in any way. Since the notch from which the plumb bob is 
hung is a pre-determined distance from the metal surface, the user has a 
set distance against which to check the plumb of the surface. optionally, 
a level bubble may be provided in the first or second leg, to further aid 
in leveling and checking plumb. Additionally a second level bubble may 
also be provided in the other leg, for further utility. Finally, a second 
magnetic strip could be provided, and the second notch could also be set a 
predetermined distance from the outer surface of that magnetic strip, or 
of the first strip, to allow the tool to be conveniently reversible in 
use. 
In view of the foregoing, several advantages of the present invention are 
readily apparent. A combination tool is provided which is highly portable 
and which combines several useful functions in a single tool. The tool may 
be used in the same manner as any carpenter's square. Additionally, it may 
be used to check plumb readings. In checking plumb readings, hands-free 
operation of the tool allows its convenient use by a single user. Optional 
level bubbles further allow the tool to be used to check level readings. 
Additional advantages of this invention will become apparent from the 
description which follows, taken in conjunction with the accompanying 
drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawings, there is depicted in FIGS. 1 and 2 a 
combined square, level and plumb tool 1 according to the present 
invention. The tool 1 includes a carpenter's square 2, preferably of the 
type commonly known as a "speed square." A speed square is a square which 
is of a size which may be conveniently carried on a tool belt, and which 
is typically used for a variety of squaring jobs, such as squaring beams, 
frames, and the like. The square 2 has two legs 6,7 set at right angles to 
one another, and a third leg 8 extending between the first two legs 6,7. A 
magnetic strip 10 is provided along either one of the legs 6,7, in this 
illustration along leg 6. This strip 10 is of sufficient magnetic strength 
to allow the tool 1 to be magnetically attached to a metal surface, 
thereby allowing hands-free use of the tool 1. 
Vertical level bubble 12 and horizontal level bubble 14 are optimally 
provided so that the tool 1 may also perform levelling operations. Having 
both a vertical level bubble 12 and a horizontal bubble 14 allows the tool 
1 to be conveniently used in a much wider range of possible orientations. 
Referring now to FIG. 2, use of the tool 1 for reading the plumb of metal 
member 16 is depicted. The tool 1 has been attached magnetically to the 
member 16 by magnetic strip 10, thereby allowing for hands-free use of the 
tool. A first plumb bob notch 18 is provided in leg 8 for receiving the 
string 20 from plumb bob 22. The string 20 is then also threaded through a 
second notch 24, and the plumb bob string reel 26 may then be suspended 
from the tool 1. Notch 18 is a pre-set distance d.sub.1 from the outer 
surface 28 of magnetic strip 10. Knowing this distance d.sub.1, the plumb 
of the member 16 may then be checked by measuring the distance d.sub.2 
from the member 16 to the plumb bob string 20. If the two distances are 
equal, then the member 16 has been determined to be perfectly vertical. If 
the distances are not equal, then necessary adjustments are indicated by 
the variance between the two distances. 
Optionally, second notch 24 could also be set at a pre-determined distance 
from surface 28 of magnetic strip 10, so that either the first or second 
notch could be used to measure plumb. Additionally, a second magnetic 
strip could also be added along leg 7, thereby allowing the tool 1 to be 
used in additional orientation. In practice, however, the tool 1 will 
generally be symmetrical so that it may be reversed and used, for example, 
on a workpiece surface which is either to the user's right or to the 
user's left. 
This invention has been described in detail with reference to a particular 
embodiment thereof, but it will be understood that various other 
modifications can be effected within the spirit and scope of this 
invention.