Abstract:
A level comprises a frame defining first and second parallel channels and first and second rails fitted slidingly in the first and second channels respectively. The level is adjustable in length by sliding the rails in the respective channels of the frame.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation-in-part of applicant&#39;s patent application Ser. No. 09/302,014 filed Apr. 29, 1999 for “Level,” now U.S. Pat. No. 6,293,023B1. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention relates to a level. 
     The conventional carpenter&#39;s level, which is used for testing whether a nominally horizontal (or vertical) surface is in fact horizontal (or vertical), within an acceptable tolerance, comprises a frame, typically made of a metal such as aluminum alloy, having at least one flat guide surface and two bubble vials mounted in the frame. The level is positioned with the guide surface against the surface to be tested. One vial is oriented relative to the guide surface for testing a nominally vertical surface and the other is oriented for testing a nominally horizontal surface. The typical level is about 2 feet long, although longer levels, e.g. four feet or six feet long, are also available. 
     The fact that conventional levels are available only in increments of about 2 feet in length gives rise to difficulty or inconvenience in using the conventional level. Imagine, for example, that you are installing a shelf inside a closet having a back wall about 3′6″ wide between two side walls. You wish to attach a support to the back wall for supporting the rear edge of the shelf The support should be horizontal, and you wish to mark the position of the support at two locations, adjacent the side walls respectively. Obviously, since the back wall is only 3′6″ wide, you cannot use a four foot level because there is not sufficient space between the two side walls. If you attempt to use a 2 foot level, you must place the markings in two steps, which is inconvenient and can cause errors. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention there is provided a level comprising a frame defining first and second parallel channels, and first and second rails fitted slidingly in the first and second channels respectively, whereby the level is adjustable in length by sliding the rails in the respective channels. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which 
     FIG. 1 is a perspective view of a level in accordance with the invention in a retracted condition, showing a central frame and first and second rails on each side of the frame, the frame and rails having flat, coplanar guide surfaces and indicators mounted in parallel and perpendicular relation to the coplanar guide surfaces. 
     FIG. 2A is a similar view of the level in a partially extended condition, showing the first and second rails slided outwardly relative to the central frame, each rail including a slide mounted within channels in the central frame, and each rail including a frame extender providing the flat, coplanar guide surface, and showing an end cap mounted at the outer end of each frame extender. 
     FIG. 2B is a cross-sectional view of the level of FIG. 1 showing an I-cross-section of the frame formed by a web plate, which includes racetrack-shaped cutouts, and guide members above and below the web plate, the guide members including outer flanges, and also showing the slides mounted in the set of channels defined by the frame, and a leaf spring in a lower left channel of the frame biasing one of the slides upward against an upper left sliding surface in a channel, and a stop mounted in a lower right channel of the frame. 
     FIG. 3 is a perspective exploded view of the level showing the central frame with channels, one leaf spring riveted in each of the two lower channels, one stop, two indicators of the bubble vial variety, and two rails each including the slide and the frame extender and a pin mounted at an end of the slide opposite the frame extender for cooperative abutment with the stop to arrest sliding motion of the rail at the extended condition. 
     FIG. 4 is a perspective view of the end of the slide opposite the frame extender, showing the narrowed portion of the slide to ease insertion of the slide into the frame channels during assembly. 
     FIG. 5 is a perspective view of the outer end of one of the rails with the end cap removed, showing the assembly of the slide, the frame extender, and a spacer, the parts being coupled together by an Allen bolt. 
     FIG. 6 is an exploded view of the rail assembly, showing a tapped holed formed longitudinally through the slide, frame extender, and spacer, and the Allen bolt for securing the parts together, the view also showing an angle formed in the end of the spacer opposite the tapped hole, the angle configured to bias the slide upwardly within the frame extender to aid in securing the slide in place. 
     FIG. 7 is a cross-sectional, perspective view of the level (cut from FIG. 11, described below) showing a rivet holding the leaf spring in place in the frame channel beneath the slide that is slidably mounted in the channel. 
     FIG. 8 is a side elevation of one of the rails of the level with a partial cutaway showing the position of the Allen bolt securing the slide, frame extender, and spacer, and showing a screw securing the end cap to the frame extender. 
     FIG. 9 is a cross-sectional view of the rail (cut from FIG.  8 ), showing the screw installed through the end cap and through the web plate of the frame extender. 
     FIG. 10 is a side elevation of the central frame with a partial cutaway showing the leaf spring mounted in one of the channels by a central rivet, the leaf spring including two wings extending left and right of the central rivet, each wing including a contact line defined between two non-coplanar portions, and showing the stop and two strips of polyethylene tape for biasing the slide against the outer flanges of the frame. 
     FIG. 11 is a side elevation, with a partial cutaway as in FIG. 10, showing the slide positioned within the channels of the frame to the extended condition, the slide compressing at its lower surface both wings of the leaf spring, and the leaf spring biasing the slide upwardly, and also showing the pin on the slide abutting the stop on the frame to prevent the slide from being moved beyond the extended position. 
    
    
     DETAILED DESCRIPTION 
     The illustrated level comprises a frame  2  and two rails  4 A and  4 B. In the following description, the suffix A or B is used when it is necessary or helpful to distinguish between the two rails or elements that are associated with the two rails. Otherwise, no suffix is used. 
     The frame  2  is preferably made from a length segment of an aluminum alloy extrusion, and can be formed of any metal, plastic or other material suitable for use as a level. Frame  2  is preferably generally I-shaped in cross-section, having two spaced parallel guide members  8 U and  8 L connected by a web plate  12  so that two pairs of upper and lower channels  20 U and  20 L are defined on opposite sides respectively of the web plate  12 . Each member  8  has at each edge a lip or flange  16  projecting toward the other member  8 . As best seen in FIG. 2B, upper flanges  16 U are preferably shorter than lower flanges  16 L. The frame has two parallel guide surfaces  24 U and  24 L. Within the two upper channels  20 U, guide member  8 U provides a pair of sliding surfaces  21 U, on each side of web plate  12 . It will be understood that the terms upper and lower are used for ease of reference to the drawings, and the invented level may generally be used in the same orientation as shown in the drawings, or inverted, and that the invention may generally be practiced with one or more components of the level disposed on either an upper or lower portion of the level with an appropriate reconfiguration of other components as necessary. 
     Each rail  4  includes a slide  28  and a frame extender  32  that is attached to the slide. 
     The frame extender  32  may be made of a length segment of the same extrusion as is used to make the frame  2  and consequently it includes two parallel guide members  36  and a web plate  40 . Preferably, frame extender  32  is formed with a cross-section identical to the cross-section of frame  2 . Frame extender  32  may be formed in a separate extrusion operation, or if formed in the same extrusion, cut to length in an operation separate from the cutting of frame  2 . The guide members  36  and the web plate  40  define two channels  42 ,  44  on opposite sides respectively of the web plate  40 . Each guide member  36  has at each edge a lip or flange  52  projecting toward the other guide member  36 . As for frame  2 , upper flanges  52 U of frame extender  32  are preferably shorter than the lower lips. The frame extender has two parallel guide surfaces  33 U and  33 L. 
     Each slide  28  includes a web plate  46  and two flanges  48  which extend perpendicular to the web plate  46 . The slide has a rebate  60  at the base of each flange. The cross-sectional configuration of the slide is selected relative to that of the channels of the frame extender so that the slide  28  can be inserted in the channel  42  in only one orientation, and in this orientation the web plate  46  of the slide is held away from the web plate of the frame extender by the flanges  48 . The slide  28  is retained in position relative to the frame extender by pins  29  . The slide does not obstruct the channel  44 . Each rail also includes an end cap  50 , which is attached to the frame extender and the slide. 
     Frame  2 , frame extenders  32 , and slides  28  are preferably formed from aluminum, or an aluminum alloy, as noted above. It will be appreciated by those skilled in the art that under some conditions aluminum does not slide smoothly against aluminum but sticks due to galling. Various treatments are available for relieving galling. The primary locations where sticking can present a problem are on the interfacing sliding surfaces of slides  28  and guide members  8 U and  8 L of frame  2 . 
     As perhaps best seen in FIG.  7  and also shown in other figures, slide  28  includes upper flange  48 U that has a sliding surface  49 U extending across flange  48 U, including rebate  60 . Sliding surface  49 U is in contact with, and slides along sliding surface  21 U of guide member  8 U of frame  2 , including flange  16 U. Lower flange  48 L of slide  28  has a sliding surface  49 L extending across flange  48 L, including rebate  60 . Flange  48 L and sliding surface  49 L are preferably substantially a mirror image of flange  48 U and sliding surface  49 U, although they may alternatively be formed in different configurations that are designed to be slidably mounted in frame  2 . 
     Friction typically exists between sliding surface  21 U of frame  2  and sliding surface  49 U of slide  28 , particularly in light of a biasing means, such as leaf spring  54 , mounted in channel  20 L of frame  2 , which urges slide  28  upwardly toward guide member  8 U and urges sliding surface  49 U against sliding surface  21 U. Leaf spring  54  is preferably made of stainless steel, and will be described in more detail below. Leaf spring  54  is in slidable, frictional contact with lower flange  48 L of slide  28  at a portion of sliding surface  49 L. The portion of sliding surface  49 L within rebate  60  may also be in sliding, frictional contact with the inner side of lower flange  16 L. To prevent sticking, it is desirable to treat one or both of each pair of contacting surfaces. Preferably, sliding surfaces  49 U and  49 L, including the portion within rebates  60 , are treated by application of a coating, which preferably includes PTFE. The coating may include a blend of about 5% to about 7% of PTFE, preferably about 6% of PTFE, mixed with a binder, such as polyester, a polyester-epoxy hybrid, or most preferably epoxy. Such a blend, which can be formed using the PTFE product of the DuPont Corporation known as Polymist® (No. F-5AEX), is coated on sliding surfaces  49 U and  49 L of slide  28  and cured at about 390° F. Coating with the PTFE blend is preferable to coating with pure PTFE because the typical curing temperature for pure PTFE is about 1,000° F., which can adversely affect aluminum. Other treatments and coating for the sliding surfaces may be substituted, or combinations of materials with low mutual coefficients of friction may be used. 
     As best seen in FIGS. 3 and 7, slide  28  has a cross-section, including sliding surfaces  49 U and  49 L and rebates  60 , designed to mate with, and slide within channels  20 U and  20 L, including flanges  16 U and  16 L. The dimensions of slide  28  are typically smaller than that of channels  20 U and  20 L. E.g., channels  20 U and  20 L may be about 0.350-inches wide between web plate  12  and flanges  16 , while the width of flange  48 , not including the rebate portion, is about 0.338-inches. A shim, such as strip of tape  70  can be installed in channel  20  to fit and position slide  28  in channel  20 . Preferably, an ultra-high molecular weight (UHMW) tape, such as the polyethylene tape made by the 3M Corporation is used. Such tape has the characteristics useful in this application of providing a low coefficient of friction, abrasion resistance, and a degree of compressability so that slide  28  will be securely slidable within the channel despite ordinary manufacturing tolerances for the channel and slide. As seen in FIG. 10, a pair of strips of tape  70  are preferably installed on frame  2 , one at each of the entrance points to channels  20 U and  20 L. Tape  70  and a narrowed portion  47  (FIGS. 3 and 4) of slide  28  facilitate insertion of slide  28  into channels  20  during assembly of the level. 
     The cross-sectional configuration of the slide  28  also allows the slide to be inserted in the channel  20  of the frame with the web plate  46  of the slide held away from the web plate  12  of the frame  2  by the flanges  48 . The slide constrains the frame extender into alignment with the frame  2 , with the two guide surfaces of the frame extender coplanar with the guide surfaces  24  of the frame. The slide  28  is slidable in the channel  20 , allowing adjustment in the length of the level between a retracted condition, in which the frame extenders abut the frame  2 , as shown in FIG. 1, through a partially extended condition, shown in FIG. 2, to a fully extended condition in which only a relatively short segment of the length of the slide is accommodated in the channel  20 . 
     The length of each slide  28  is approximately equal to the sum of the length of the frame  2  and the lengths of the two frame extenders  32 . The slide of the rail  4 A then extends through one pair of upper and lower channels  20 U,  20 L of the frame  2  and into the channel  44  of the rail  4 B when thy level is in the retracted condition. Likewise, the slide of rail  4 B then extends through the pair of upper and lower channels  20 U,  20 L on the other side of web plate  12  and into the channel  44  of the rail  4 A when the level is in the retracted condition. This allows the maximum difference in length between the retracted condition and the fully extended condition. 
     The frame also preferably includes, in each lower channel  20 L, a leaf spring  54  Alternatively, two leaf springs can be mounted in each channel  20 L, particularly with a longer level. The level is nominally about 2-feet long in the retracted condition and about 4-feet long in the extended condition. The level can be manufactured in shorter or longer lengths, including a 4-foot retracted length extendible to 8-feet, and any intermediate length. The leaf springs  54  are preferably attached to guide member  8 L and both leaf springs  54  urge slides  28 A,  28 B toward the guide member  8 U. Alternatively, one of the leaf springs may be attached in channel  20 U to urge one slide toward guide member  8 L and the other leaf spring attached in channel  20 L to urge the other slide toward guide member  8 U. The leaf springs take up clearance between the slides  28  and the frame  2 . 
     The web plate  12  is formed with an aperture in which two indicators, such as bubble vials  56  are mounted. One of the vials is oriented for testing a vertical surface and the other is oriented for testing a horizontal surface. The bubble vials  56  project from the web plate  12  into the channels  20  of the frame  2 . Since the web plate  46  of the slide  28  is held away from the web plate  12  of the frame  2  by the flanges  48 , the web plate  46  remains clear of the bubble vials  56  when the slide is inserted in the channel  20 . Similarly, the web plates  40  are each formed with an aperture in which two indicators, such as bubble vials  58  are mounted. The bubble vials  58  project from the web plate  40  into the channels  42 ,  44  of the frame extender. Since the web plate  46  of the slide  28  is held away from the web plate  40  of the frame extender by the flanges  48 , the web plate  46  of the slide  28  remains clear of the bubble vials  58 . Moreover, when the level is compressed from its extended condition to its retracted condition, and the slide  28  of one rail enters the channel  44  of the other rail, the web plate  46  remains clear of the bubble vials  58  of the other rail. The bubble vials  58  are thereby protected from damage by impact with the slide. 
     The interaction of the components of the level as frame  2  and rails  4  are moved between the retracted and extended conditions is best seen in FIGS. 10 and 11, where leaf spring  54  is shown mounted to channel  20 L, preferably by a central mount such as single rivet  72 , or by other suitable means. Leaf spring  54  includes two wings  74 ,  76  extending left and right of mount  72 , each wing having a convex shape, preferably formed by pre-bending wings  74 ,  76  at a contact line  78 ,  80 , respectively. As best seen in FIG. 11, sliding surface  49 L of slide  28  preferably contacts leaf spring  54  substantially only at contact lines  78 ,  80 . Alternatively, other biasing means can be used. Leaf spring  54  preferably urges slide  28  upwardly with at least about 22-lbs of force. The convex shape of leaf spring  54  minimizes the amount of contact surface between spring  54  and slide  28  and also facilitates insertion of slide  28  into channel  20 L during level assembly. 
     The biasing of slide  28  by spring  54  provides for a frictional sliding of slide  28  relative to frame  2  that is easily movable by a user, while at the same time substantially fixing the slide in place at any position relative to frame  2  by frictionally holding slide  28  in frame  2 . Thus, a user can position the slide to any position between and including extended and retracted, use the level, and then set the level down in any orientation, and the frictional hold prevents the level&#39;s condition from changing despite gravity&#39;s acting on the level components. 
     The level is shown in the extended condition in FIG. 11 with slide  28  moved as far outwardly as possible because pin  29  is abutted against a stop, such as rubber or neoprene piece  82  installed, e.g., by gluing, in channel  20 L. Alternatively other methods of limiting the outward movement of slide  28  may be used. During assembly, pin  29  is preferably not installed on slide  28 , allowing insertion of the slide into the channel. Pin  29  is preferably installed after assembly. 
     Slide  28  is typically shorter than the distance between channels  20 U and  20 L. E.g., channels  20 U and  20 L may measure about 2.050-inches from sliding surface  21 U to a corresponding surface  21 L on channel  20 L, while slide  28  may measure about 1.980-inches between sliding surfaces  49 U and  49 L. Leaf spring  54  takes up the difference in the heights of the slide and the inside of frame  2 , positioning and urging slide  28  against upper sliding surface  21 U. Thus, while flanges  16 L of frame  2 , and corresponding flanges  52 L of frame extender  32  are preferably taller than flanges  16 U and  52 U, upper and lower rebates  60  of slide  28  are preferably identical in size, and slide  28  fits appropriately in channels  20 U and  20 L for controlled, slidable motion, because slide  28  is biased upwardly within the frame. A spacer, such as stainless steel bar  84  (FIGS. 5,  6 , and  8 ) is preferably installed in frame extender  32  to position slide  28  within frame extender  32  in generally the same relative position as spring  54  positions slide  28  within frame  2 . The web plates  12  and  46  are formed with openings which serve to reduce the weight of the level and facilitate gripping and handling of the level. The openings also provide viewing access to the bubble vials, so that regardless of the degree of extension of the level, the user can see at least one vial oriented for testing a vertical surface and one vial oriented for testing a horizontal surface. 
     The manner of use of the level, for testing a nominally vertical or nominally horizontal surface, or for marking segments of a horizontal or vertical line on a vertical surface, will be well understood by a person skilled in the art. 
     In use of the level illustrated in the drawings, for example in a confined space, the user extends the rails from the frame sufficiently to span the desired distance without interference with other structures, and the user can then determine whether a nominally horizontal (or vertical) surface is in fact horizontal (or vertical) or can mark a horizontal (or vertical) line on a vertical surface between two structures that would interfere with a longer level. Further, it is possible to manipulate the level into a confined space in its retracted condition and then extend it for use, e.g. in marking a vertical or horizontal line on a wall. 
     The construction of the rails is best seen in FIGS. 5,  6 , and  8  where slide  28  is inserted into frame extender  32  so that the ends of each are generally flush. As described above, spacer  84  positions slide  28  in frame extender  32  to match the position of slide  28  in frame  2 . Spacer  84  preferably includes a bend  86  that gives spacer  84  a convex shape to increase a frictional hold between slide  28  and frame extender  32 . A shim, such as strip of UHMW tape  88  is preferably applied at entrance portions of upper and lower channels  42 U and  42 L of frame extender  32  to position slide  28  within frame extender  32 . Slide  28  preferably bares a width and height relationship to frame extender  32  as that described above for slide  28  and frame  2 . 
     Slide  28 , frame extender  32 , and spacer  84  preferably are assembled together by drilling a hole  90  longitudinally through slide  28 , frame extender  32 , and spacer  84 . Hole  90 , which is roughly centered on spacer  84 , is then tapped, and the rail components are secured together, preferably by an Allen bolt  92  screwed into hole  90 . 
     The construction and affixing of end cap  50  is best seen in FIGS. 8 and 9, where end cap  50  can be seen to include two lobes  94  that fit over each side of web plate  40  of frame extender  32 . A fastener, such as screw  96  affixes end cap  50  to frame extender  32 . End cap  50  is preferably formed of a plastic material, and provides a rounded, cushioned end to the level. 
     It will be appreciated that the invention is not restricted to the particular embodiment that has been described, and that variations may be made therein without departing from the scope of the invention as defined in the appended claims and equivalents thereof.