Abstract:
A portable expandable project plan table includes a table top that is pivotally connected to a frame having a generally truncated right triangular prism shape. The table top is hinged to permit access to storage for drafting tools and papers within the frame and may be locked to prevent movement when the table is transported. The legs of the table pivot between vertical for use and horizontal for transporting, and are designed to overlap in the folded position in a compact arrangement. Each leg is independently height adjustable to permit the table to be made level on uneven surfaces, and wheels on each leg facilitate movement of the table in the open-for-use position. The table is constructed of durable materials to permit use out of doors or in adverse conditions.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to the field of portable tables, and more specifically to portable expandable project tables. 
     There are numerous applications requiring a versatile portable project table. For example, workers in the construction industry commonly require an on-site table to support blueprints, plans, specifications, technical drawings and other information. Routine working conditions demand a table that is suitable for outdoor use. These conditions include wind, rain, and other adverse weather conditions, uneven terrain, and frequent on-site relocation. Portability, including convenient vehicle transportability, is essential for tables. Despite the need for portability, project tables must be sturdy and adaptable to numerous applications. The ability to expand the table surface is also needed in many applications. 
     BRIEF DESCRIPTION OF THE PRIOR ART 
     Prior art drafting tables are unsuited for applications as described above in that they are commonly constructed exclusively for indoor use with limited mobility. As such, they have limited adjustability, are not constructed to withstand outdoor weather conditions, and are not readily transportable. Portable tables are commonly constructed to be lightweight rather than hardy. A folding portable drafting table representative of the prior art is described in U.S. Pat. No. 5,315,935 to Weisenfels. The table is constructed of light-weight wood, and will necessarily be unsuitable for use in typical outdoor conditions including wind or moisture. It is not height adjustable, nor can it be adjusted for uneven surface conditions. While portable, the basic table requires that three separate pieces be carried separately, it is not expandable, and it is not readily apparent that it can be moved without disassembly and reassembly. U.S. Pat. Nos. 4,372,631 to Leon and U.S Pat. No. 4,099,469 to Sahli also describe foldable drafting tables. Both tables are designed to fold only for ease of storage in a small space and they cannot be easily transported from one job site to another. The table described by Leon has wheels to facilitate movement only from room to room within a single building. Neither table is adjustable by height to accomodate various user requirements. Also, neither table is expandable or adjustable to accomodate any site condition other than a flat floor. U.S. Pat. No. 5,598,789 to Jonker describes a vertically adjustable table, the use of which would be limited to a relatively flat floor. It is not intended, and would not be suitable, for outdoor use or for convenient vehicle transportability. 
     Accordingly, there is a need for a portable drafting table that is suitable for on-site construction site use or use in other locations where hardiness is important. Such a table will be sturdy enough to withstand heavy use and adverse weather conditions. It will also be adjustable to accomodate sitting and standing users as well as uneven terrain. It will ideally have rollers for easy movement and will be expandable to accomodate unusually large drawings. Finally, it will fold compactly for easy carrying and transport by vehicle. 
     SUMMARY OF THE INVENTION 
     The present invention is a portable drafting table that folds compactly for convenient transport by vehicle, but is of sturdy construction to permit on-site construction project use. The legs of the table are independently adjustable to accommodate both the table surface height requirements of individual users and also level positioning on uneven terrain. The table top opens to expose a storage space within the frame. The frame also includes a storage drawer and a carrying handle for transportability. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages of the invention will become apparent from a study of the following specification when viewed in light of the accompanying drawing, in which: 
     FIG. 1 is a perspective view of a preferred embodiment of the folding table; 
     FIG. 2 is a perspective view of the table frame and table top in an open position; 
     FIG. 3 is an elevation view of an inner adjustable table leg; 
     FIG. 4 is a detailed top cutaway view of a table leg, illustrating a locking pin securing an outer fixed table leg and an inner adjustable table leg; 
     FIG. 5 is a front elevation view of an optional table extension; 
     FIG. 6 is a front elevation view of an optional plan holder; 
     FIG. 7 is a detailed illustration of a table extension securing mechanism; and 
     FIG. 8 illustrates a snap-in shoe suitable for use with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, a preferred embodiment of a portable expandable project plan table  20  according to the invention has a flat-surfaced table top  22  supported by a table frame  24 . Table frame  24  has the general shape of a truncated right triangular prism having base, right and left side, front and back surfaces. Table top  22  is positioned atop the frame  24  to enclose the frame  24  when the table top  22  is in its closed position. Because frame  24  is deeper at the back than at the front, the table top  22  slopes downwardly from rear to front. The length and width of table top  22  is preferably somewhat greater than that of table frame  24  to create an overhang or lip to table top  22  along the front and both sides of frame  24 . In a preferred embodiment, the lip is about 1 inch, but it may be varied at the discretion of the fabricator. The table, including the legs to be described below, is preferably made from a light-weight, but durable and strong, material such as aluminum. The aluminum-to-aluminum connections for the table legs and accessory attachments described herein is preferably welded. 
     Table top  22  is preferably secured to table frame  24  along the upper back edge of frame  24  by a piano hinge  25 . Raising the front edge of table top  22  to its open position reveals a storage space  27  suitable for placing drawings, instruments or other items. Hydraulic arms  23  are affixed on each side to table top  22  and table frame  24  to hold table top  22  in a raised position and allow it to be controllably opened and closed without slamming. The hinge  25  is secured to the table top  22  and frame  24  by an aluminum weld. Alternatively, it may be secured by other devices such as rivets, bolts, or screws. 
     A leg bracket is rigidly fixed and extends downwardly at each corner from the base of table frame  24 . In the preferred embodiment illustrated in FIG. 1, right side leg brackets  26  are relatively shorter than left side leg brackets  28  as will be explained more fully below. It will be readily apparent, however, that the invention will work equally well if the right side leg brackets  26  are relatively longer than left side leg brackets  28 . Each table leg has an outer table leg segment and an inner table leg segment. Right side outer table leg segments  30  are pivotally secured to brackets  26  by a pivot pin such that table leg segments  30  may pivot in a 90 degree arc between vertical and horizontal underneath table frame  24 . A fixed side leg brace  34  secures the right side outer table leg segments  30  together and provides fore-and-aft support to them. Left side leg brackets  28  are similar to right side leg brackets  26  except that brackets  28  are relatively shorter. Left side outer table leg segments  36  are pivotally secured to brackets  28  by a pivot pin  32  such that table leg segments  36  may pivot in a 90 degree arc between vertical and horizontal underneath table frame  24 . A fixed side leg brace  34  secures the left side outer table leg segments  36  together and provides fore-and-aft support to them. 
     At both the front and rear of the table  20 , a right side folding leg brace  38  is pivotally connected to table frame  24  and the table leg segment  30  to both permit the right table legs to fold under frame  24  and to restrict the table legs from rotating beyond the vertical away from the table. A pivot pin  40  at the center of folding leg brace  38  permits the table legs to fold under table frame  24 . Any suitable device, a number of which are well-known in the prior art, may be used to lock the folding leg brace  38  in position when the table legs are extended for use. Similarly, at both the front and rear of the table  20 , a left side folding leg brace  40  is pivotally connected to table frame  24  and the table leg segment  36  to both permit the left table legs to fold under frame  24  and to restrict the table legs from rotating beyond the vertical away from the table. A pivot pin  40  at the center of folding leg brace  42  permits the table legs to fold under table frame  24 . It will be readily apparent to one skilled in the art that right folding leg brace  38  is longer than left folding leg brace  42  to accommodate the differences in length between right side leg bracket  26  and left side leg bracket  28 . 
     The left side table legs  36  fold compactly under the right side table legs  30  in an overlapping, or nesting, arrangement, due to the relatively longer length of right side brackets  26  as compared to left side brackets  28 . It will be readily apparent to one skilled in the art how to determine the precise lengths of the various components to obtain the desired compact arrangement. 
     Each of the outer table leg segments  30 ,  36  is adapted to receive an adjustable inner table leg segment  44  in telescoping arrangement. As is illustrated more clearly in FIGS. 1 and 3, each adjustable inner table leg segment  44  has a plurality of evenly spaced holes  46  on a first surface thereof. Each of the fixed outer table leg segments  30 ,  36  has a hole  48  of substantially identical diameter to holes  46  and positioned to successively align with each of the holes  46  as the adjustable inner table leg segment  44  is moved relative to the outer table leg segments  30 ,  36 . A spring tension peg  50  mounted through hole  48  on each of the outer table leg segments  30 ,  36  engages hole  46  when holes  46  and  48  are aligned to lock inner table leg segment  44  in place, as is illustrated in FIG.  4 . Inner table leg segment  44  has a socket  52  affixed at its lower end to receive the stem of a swivel “snap-in” non-marring caster wheel  54 , as is well known in the prior art. The diameter and material of caster wheel  54  may be varied to maximize mobility on different surfaces such as finished or unfinished interior floors or uneven outside terrain. Alternatively, a snap-in aluminum shoe  55 , as illustrated in FIG. 8, fitted with a rubber base  57  may be substituted for caster wheel  54  when it is desired that the table be more securely positioned in a fixed location. 
     As illustrated in FIG. 2, two non-threaded receivers  56  are placed on the right side of table frame  24  for mounting optional table extensions. Two additional non-threaded receivers are similarly mounted on the left side of table frame  24 . A suitably sized aluminum spacer  59  is preferably inserted between frame  24  and a table extension. FIG.  5 . illustrates a first optional table extension in the form of a table expansion  58 . Table  58  has a top surface  60  and a frame  62  having a shape such that top surface  60  and table top  22  are coplanar when table expansion  58  is positioned adjacent frame  24 . On one side of frame  62  are two threaded receivers  64  positioned to align with non-threaded receivers  56  when table expansion  58  is positioned adjacent table  20 . FIG. 7 illustrates a preferred securing mechanism for securing table expansion  58  to table frame  24 . A wing bolt  66  is passed through non-threaded receiver  56  of table frame  24  and threaded into the threaded receiver  64  of table expansion  58 . A leg table brace  68  secured between the bottom of table expansion  58  and side leg brace  34  provides additional support for the table expansion  58 . 
     FIG. 6 illustrates a second optional table extension in the form of a plan holder  70 . Plan holder  70  has a horizontal top surface  72  and a frame  74 . On one side of frame  74  are two threaded receivers  64  positioned to align with non-threaded receivers  56  when plan holder  70  is positioned alongside table  20 . FIG. 7 illustrates a preferred securing mechanism for securing plan holder  70  to table frame  24 . A wing bolt  66  is passed through non-threaded receiver  56  of table frame  24  and threaded into the threaded receiver  64  of plan holder  58 . A leg table brace  68  secured between the bottom of plan holder  70  and side leg brace  34  provides additional support for the plan holder  70 . 
     The versatility of the invention is substantially enhanced with the inclusion of a drawer  72  provided through the front surface of frame  24 . A handle  76  permits opening and closing of the drawer  72 , and a lock  74  permits drawer  72  to be locked for security and to prevent accidental opening when the table  20  is transported. Similarly, a lock  78  is provided to secure table top  22  to frame  24 . Lock  78  both prevents access to the storage space  77  within frame  24  and also prevents accidentally opening of table top  22  when the table  20  is being transported. 
     Locks  74  and  78  are preferably keyed, lockable cam locks. Alternatively, a non-locking clasp of which there are many suitable types well-known in the prior art may be substituted in place of locks  74  and  78  if physical security is not considered necessary or desirable. A handle  80  is secured near the mid-section of the front surface of frame  24  to facilitate transportability of the table  20  when it is folded. 
     While the preferred forms and embodiments of the invention have been illustrated and described, it will be apparent to those of ordinary skill in the art that various changes and modification may be made without deviating from the inventive concepts set forth above.