Abstract:
An offset tape measuring tool marked with standard English measurements includes integrated indicia for quick determination of distance between bends for a given offset depth and offset angle when installing conduit. Additional indicia may be included for the measurement of the shrinkage of the conduit with respect to the specified offset depths and angles. The integrated invention may be part of a standard tape measure strip to provide a convenient multi-purpose tool. The tool eliminates any external calculations or table reference typically necessary when bending conduit to clear an obstacle.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to a measuring strip, and more particularly to a strip that may be used to measure offsets in rigid steel conduit, electrical metallic tubing, galvanized rigid conduit, rigid aluminum conduit and the like.  
           [0002]    When installing conduit to house runs of conductors, the installer inevitably will need to make bends in the conduit run in order to navigate around obstacles. Bends of various shapes are usually needed, such as right angle or 90-degree bends, offsets and saddles. Most, if not all, of these bends will be made on the job as part of the installation procedure and are, therefore, known as field bends.  
           [0003]    Before these field bends are actually made, it is essential that the installer do some careful planning. As each bend in the run adds to the friction caused when pulling the conductors, the NEC allows for only a total of 360 degrees of bends between pull points. As more bends are made, more pull points are required. This accordingly will affect the required labor to install the conductors, and ultimately affects the schedules and profits of the job. Therefore, it is good practice for the installer to walk the entire route before any conduit is installed, especially when dealing with longer runs with difficult conductor installation.  
           [0004]    The schedules and profits of the job are further affected by the labor and material costs involved in the installation of the conduit, and, as such, accurate measurements are crucial. While installing electrical conduit for example, it will be necessary to calculate the correct length for a specific run. Because most installations are typically not straight runs, these bends must be made to navigate around obstructions to ensure a precise fit. When two opposing bends that are equal in the degree of their angle are used to clear an obstacle and maintain a course parallel to the original course, it is called an offset bend. In other words, and assuming both bends have the same angle measure, an offset bend is used when an obstruction requires a change in the conduits&#39; plane.  
           [0005]    Before making an offset bend, the installer must choose the most appropriate angle for the offset. Although this angle may be primarily chosen with respect to the offset depth, shallow bends will make for easier conductor pulling, while steeper bends will conserve space. Additionally, the installer must also consider that the conduit will shrink due to this detour. This shrinkage or take-up may possibly be ignored if working away from the obstruction, but certainly must be considered when working into the obstruction.  
           [0006]    After the installer determines the offset depth and offset angle necessary to clear the obstacle, he will then typically refer to an offset multiplier table to calculate the required distance between conduit bends to achieve the desired dimensions. An example of such an offset multiplier calculation is illustrated below in Table 1.  
                                               TABLE 1                           Offset Multiplier                    = Distance between bends       Offset Depth   X Constant Multiplier   Column 3       Column 1   Column 2   SHRINK PER INCH OF       ANGLE   MULTIPLIER   OFFSET DEPTH                    10° × 10°   6   1/16″   per inch       22 1/2° × 22 1/2°   2.6   3/16″   per inch       30° × 30°   2   1/4″   per inch       45° × 45°   1.4   3/8″   per inch       60° × 60°   1.2   ½″   per inch                  
 
           [0007]    To use this table, the installer locates the measured offset angle on the left or first column, then taking the corresponding multiplier constant of column 2, he multiplies this constant by the measured depth of the offset to determine the distance between the offset bends. For example, if the depth of the offset is 5″ and the offset angle is 30°, then, according to the Table, 30° corresponds to a 2 constant so that the distance between bends is 5″×2 or 10″. The table further provides for the corresponding shrinkage due to the detour. In this example, the shrinkage (column 3) is 5″×¼″ per inch or 1¼″ shrinkage.  
           [0008]    Tables such as those illustrated by Table 1 certainly aid the installer that encounters the prescribed offset angles depicted by such tables. However, if the installer encounters an offset angle that is not depicted in his table, he must either approximate the measurement or determine the exact distance between bends through the use of trigonometry. As the multiplier constant in these tables is the cosecant of the angle of offset, a complete chart of Natural Trigonometric Functions illustrates all of the constants for any particular degree of offset. Obviously, such a complete chart would hinder the installer at the job site, so smaller tables illustrating the most common offset angles are more commonplace.  
           [0009]    In any event, this procedure, when used properly, is an adequate method for the offset bending of conduit runs, but it is often time consuming to refer to tables and make calculations as well as prone to error due to careless approximations. Whenever a mistake is made installing conduit it costs money both in the form of labor and materials. An invention that eliminates this error would be most beneficial to the art because it would eliminate the waste and added expense caused by such errors.  
           [0010]    In light of the preceding problems, there has been an effort in the art to develop quick guides for installer use in bending conduit. One such effort, for example, has been developed to incorporate an offset calculator for 45° angles onto a standard tape measure strip. The Trubend™ 45° Offset Calculating Tape Measure attempts to accomplish this goal. Basically, the strip has a standard scale at the top of the rule by which the height of the obstruction is measured. The corresponding measurement on the bottom of the rule is used to measure the spacing between the 45° bends.  
           [0011]    However, this method fails to incorporate easily readable pre-marked indicia that illustrate the correct distance between bends of known offset depths and angles. While it does have an offset multiplier table on the back side of the strip for other angles, the installer still must find the correct multiplier constant, make a calculation, and then re-measure for the correct distance.  
           [0012]    Other attempts to reduce human error when determining the lengths of piping required for given angles are shown in U.S. Pat. Nos. 2,389,369, 4,696,110, and 4,811,489. All three of these patents have indicia for standard measurement with some form of an additional table or indicia for determining lengths of pipes. Specifically U.S. Pat. Nos. 4,696,110 and 4,811,489 have disclosed tables for determining the take off (or shrinkage) of pipes when using elbow and 45° angle fittings. However, these inventions fail to satisfy the niche required for precise determination of the distance between conduit tubing bends for all of the most commonly used offset angles quickly and precisely.  
           [0013]    In view of the aforementioned needs and the shortcomings of the prior art, it is, therefore, a general object of the present invention to provide a measuring strip that will provide typical measuring indicia with integrated indicia for precise measurement of the distance between bends required to allow a specified offset depth and offset angle for electrical conduit installation.  
           [0014]    It is another object of the present invention to eliminate the need for additional reference tables for determining offset distances.  
           [0015]    It is yet another object of the present invention to reduce error and waste created from incorrect approximations and calculations.  
           [0016]    Still another object of the present invention is to save time required to install conduit by eliminating steps required to determine the distances between offset bends.  
           [0017]    Another object of the present invention is to provide a measuring strip that will provide typical measuring indicia with integrated indicia for the precise measurement of the shrinkage of conduit with respect to specified offset depths and angles.  
           [0018]    These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.  
         SUMMARY OF THE INVENTION  
         [0019]    According to the present invention, there is provided an offset measuring device having a measuring strip with an upper surface with a plurality of numerical instrumental line markers spaced thereon. Offset indicia are spaced along some of the markers and have a pair of representative measurements, one for offset depth and one for offset angle, associated therewith for determining the distance between offset bends of a conduit. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with the further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:  
         [0021]    [0021]FIG. 1 is a perspective view of the preferred embodiment of the offset tape constructed in accordance with the principles of the present invention.  
         [0022]    [0022]FIG. 2 is a rear perspective view of the housing illustrating the belt clip of the apparatus.  
         [0023]    [0023]FIG. 3 is a top perspective view of the measuring tape of the apparatus illustrating the pre-marked indicia for offsets of varies degrees.  
         [0024]    [0024]FIG. 4 is an enlarged view of a general indicia of FIG. 3.  
         [0025]    [0025]FIG. 5 is a top perspective view of a run of conduit before and after the offset bends are applied.  
         [0026]    [0026]FIG. 6 is a side elevational view illustrating the marking and bending process with respect to a length of conduit. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    Referring now to the Figures, and in particular to FIGS. 1 and 2, the preferred embodiment of the offset tape measure embodying the principles and concepts of the present invention and generally designated by the reference numeral  10  will be described. Although the preferred embodiment will be described with respect to a retractable tape case, it will be appreciated that the present invention is applicable to any measuring device. For example, a folding rule, steel rule, wind-up flexible tape, wooden fixed rule, plastic fixed rule, markings on a level, or any other such markable device may be used. In any event, the offset tape measure of the preferred embodiment basically comprises a housing  12 , a measuring tape  14  rolled and enclosed therein and a hook or flange member  16 . More particularly, the housing  12  is formed in the conventional rectangular configuration with a front surface  18 , a rear surface  20  and essentially hollow interior. The housing  12  is divided into front  22  and rear  24  halves coupled together by a plurality of screws  26 .  
         [0028]    The front side wall  28  has an aperture  30  extending through it and into the hollow interior. The front side wall further has an upper extent which includes a slidable switch or lock  32  coupled to it. This lock is movable in an upward or downward direction along the plane of the upper portion of the front wall. The lock further includes a plurality of grooves  34  to provide a firm gripping surface for the users thumb, for example. The housing may additionally include a belt clip  34  and/or a rope aperture  38 .  
         [0029]    The measuring tape  14  is formed in elongated planner rectangular configuration and will preferably be in measures of conventional distance. The tape  14  has an outboard end which includes a flange  16  which is positioned around an object when utilizing the apparatus. The tape  14  is linearly extendable from the housing  12  in an operative orientation. As the housing  12  includes a tape rolling means, the tape  14  is rolled within the hollow interior of the outer housing and operatively coupled to the tape rolling means in a stored orientation. Upon release of the tape  14  it retracts within the hollow interior of the housing.  
         [0030]    Referring now to FIG. 3, the tape  14  has an upper surface  40  with a top edge  42  and a bottom edge  44 . The top edge including numerical instrumental line markers  46  spaced preferably {fraction (1/16)} of an inch from each other. The top edge further including inch demarcation numerals  48  positioned at each one inch interval. Within the center portion of the upper surface  40  are spaced pre-marked offset indicia or symbols  50  along with a master symbol  52  with key or legend  54 .  
         [0031]    An enlarged indicia  56  and key  58  are shown in FIG. 4 with reference thereto, the present invention provides for multiple offset depths and angles in determining the distance required between offset bends of the conduit, as well as the associated shrinkage for each combination thereof. More particularly, offset depth “A”  60  with an offset angle of “X°”  62  requires the distance “d”  64  between bends, and a shrinkage of “a”  66 . While offset depth “B”  68  with an offset angle of “Y°”  70  and a shrinkage of “b”  72  also requires the distance “d”  64  between bends. It will be appreciated that the present invention may use a single depth and angle measurement per indicia to indicate distance between bends markers, or may use more than two depth and angle measurements per indicia.  
         [0032]    In practice, to cut down on labor and materials, the conduit installer desires to make straight runs from feed to feed, as the top run of conduit  74  of FIG. 5 illustrates. However, when an obstacle  76  is in the path of the run and the run is into the obstruction, one of the best solutions is the offset bend illustrated in the bottom run of conduit  78  in FIG. 5. The present invention provides a quick determination scheme whereby the installer first decides what offset angle and offset depth combination are necessary for the conduit to clear the obstacle and where to place the first bend. The location of the first bend is obtained by simply adding the distance to the obstruction  80  to the associated shrinkage “a” as indicated on the tape for that particular offset depth and angle combination. After marking the first bend  82  the measure  14  is placed such that the end of the tape  16  is at the mark for the first bend  82 . The installer then finds the indicia on the tape to match up the specified offset depth with the offset angle as enlarged in FIG. 4. A mark can then be made at that point to delineate the second bend  84 .  
         [0033]    Once properly marked using the principles of the present invention, the conduit can then be bent using conventional methods to produce the specified offset depth and offset angle. Such methods include mechanical benders, hydraulic benders and most commonly field foot benders. FIG. 6 illustrates a field foot bender  86  including a foot rest  88 , handle  90 , lip or hook  92  and bender arrow  94 . The bender arrow  94  is aligned with the mark  82  for the first bend after the conduit is placed on the floor. One foot is placed on the footrest  88  and with the handle  90  in both hands, pressure is applied to the footrest as the handle is pulled until the bender reads the correct angle X°  62 . The same procedure is used to bend the other side of the offset after the conduit is inverted on the floor. Once the bends are completed, the conduit can be installed around the obstacle  76 , see run  78  of FIG. 5. Note that a certain distance of the run is lost when making the offset bends. This shrinkage or take-up distance  96  is dependant upon the angle used and depth of the offset. As discussed, this shrinkage must be taken into account when determining the total length of the conduit run.  
         [0034]    As a practical example, assume the installer ran into an obstruction that required an offset depth of 5 inches and an offset angle of 45°. After the location of the first bend is determined, the tape measure strip  14  would be placed with the strip end  16  at the mark for the first bend. With the strip extended the installer would find the 5 inch offset mark  98  (“A”) and then the 45° offset angle mark  100  (X°) as shown in FIG. 3. This point,  7 ″ ( 102 ), is exactly where the mark needs to be made for the second bend. Note that in this example, the conduit will in effect shrink 1⅞″ ( 104 ). By utilizing the indicia of the present invention, the installer has bypassed having to look up a multiplier, make a calculation and then re-measure to mark the second bend.  
         [0035]    The most frequently used angles are shown in FIG. 3. While it is understood that other variations of this depiction are within the scope of this invention, color-coding or any other means may be used to distinguish different offset angles or different offset depths to allow the strip to be used faster. Additionally, a second axis may be used on the bottom of the strip for an alternative scale such as metric. Furthermore, a small table may be included with the offset multipliers for unique depth and angle combinations.  
         [0036]    While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made therein without departing from the invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.