Abstract:
A portable, parallel straightedge drafting board is disclosed which utilizes a unique wire arrangement with control locks attached thereto to achieve a movable straightedge that will always be parallel to itself when moved during use of the drafting board.

Description:
RELATED APPLICATION 
     This utility patent application claims benefit under U.S. Provisional Patent Application No. 61/597,968, entitled “Parallel Straightedge Drafting Board”, filed on Feb. 13, 2012. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to drafting boards and more particularly to a cord mounted straightedge assembly in proper movable position on a drafting board. 
     BACKGROUND OF THE INVENTION 
     In the prior art, portable drafting boards have moveable straightedges that maintain a fairly good parallel orientation as the straightedge moved up and down the drafting board. However, the mechanisms for maintaining parallel orientation of the straightedge as is it moved have limited compensation for any error on the left side of the drafting board to the right side of the board to maintain the straightedge parallel to previous positions as it is moved. 
     SUMMARY OF THE INVENTION 
     A straightedge drafting boards is described that is simple in design but has the ability to maintain a straightedge mounted on the drafting board in continuous parallel orientation as the straightedge is moved up and down the board. 
     To provide for this compensation a single cord is connected between the left and right side edges of the drafting board and the left and right ends of the straightedge are connected to this cord. Any position of the single cord and the left end of the straightedge connected thereto along the left side of the drafting board is reflected via the single cord to the position of the single cord along the right side of the drafting board. This better maintains the straightedge mounted on the drafting board in continuous parallel orientation as the straightedge is moved up and down the board. 
    
    
     
       DESCRIPTION OF THE DRAWING 
       The invention will be better understood upon reading the following Detailed Description in conjunction with the drawing in which: 
         FIG. 1  is a perspective view of the drafting board when it is set up; 
         FIG. 2  is a bottom view of the drafting board showing how a single cord is routed and is connected to either end of a straightedge; 
         FIG. 3  is a side view of one of two adjustment bracket and brake knob mechanisms, one being connected to either end of a straightedge and to the single cord as it is positioned along either side of the drafting board; and 
         FIG. 4  is shown a lock mechanism that is used to maintain the drafting board in an inclined position when in use. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1  is a perspective view of the drafting board assembly  10  when it is set up for use. Board assembly  10  comprises a flat board  11  having a carrying handle  12  that used to both carry board assembly  10 , and also to rotate a rod elevation piece  20  from a position folded up against the bottom of board  11 , as shown in  FIG. 2 , to the extended position as shown in  FIG. 1 . Handle  12  is firmly fixed to rod elevation piece  20 . On the bottom corners of rod elevation piece  20  are feet  13   a  and  13   b , one toward each side of the board  11 . In their extended position, as shown in  FIG. 1 , rod elevation piece  20  is locked in its extended position by two snap lock mechanisms  21  (not shown in  FIG. 1 ) on the bottom of board  11 . Snap lock mechanisms  21  are shown in and described with reference to  FIGS. 2 and 4 . 
     In  FIG. 1  are shown pulley  15   a  in the upper left of drafting board assembly  10  and pulley  15   b  in the lower left corner of board  11 . There is a duplicate pulley  15   c  (not shown in  FIG. 1  but shown in  FIG. 2 ) in the upper right corner of drafting board assembly  10  and another pulley  15   d  (also not shown in  FIG. 1  but shown in  FIG. 2 ) in the lower right corner of board  11 . The pulleys  15   a - 15   d  are described in greater detail with reference to  FIG. 2 . Also shown is straightedge  25  which can slid up and down board  11  and remain parallel to all previous positions of straightedge  25 . When in a particular, desired position straightedge  25  is locked in that position using edge locks of control elements  17   a  and  17   b  which are shown in and described in greater detail with reference to  FIG. 3 . 
     Straightedge  25  is made of extruded and machined aluminum and a novel control element  17   a  attached to the left end and control element  17   b  attached to the right end thereof. Control elements  17   a  and  17   b  includes other elements that are shown in and described with reference to  FIG. 3 . Control element  17   a  is mounted on the left edge of board  11  and control element  17   b  is mounted on the right edge of board  11 . On control element  17   a  is shown a brake knob  23   a  and a top adjustment knob  26   a , and on control element  17   b  is shown a brake knob  23   b  and a top adjustment knob  26   b . The function of the knobs are described with reference to  FIG. 3 . 
       FIG. 2  shows a bottom view of the drafting board  10  showing how a single cord  16  is routed around the edges of board  11  and is connected to either end of straightedge  25  (not seen in this Figure) by control elements  17   a  and  17   b.    
     There is also rod elevation piece  20  that is made of rigid steel rod so it will not easily bend. Rod elevation piece  20  is formed in a closed loop as shown and handle  12  firmly attached to the middle of the top of the loop as shown. A piece of the loop of elevation piece  20  passes through snap lock mechanisms  21   a  and  21   b  as shown, where it is held by a cover. The snap lock mechanisms  21   a  and  21   b  are each fastened to the underside of board  11  where shown. Attached to the lower corners of closed loop rod  20  are feet  13   a  and  13   b  which provide friction preventing or limiting movement of drafting board  10  when it is set up on a table or other surface. Snap locks  21   a  and  21   b  are better shown in and described with reference to  FIG. 4 . 
     In each of the four corners of board  11  is fastened a wire guide  15   a ,  15   b ,  15   c ,  15   d , each wire guide consisting of a plate with a small pulley attached thereto. The axis of the shaft on which the pulleys are mounted extends downward from and perpendicular to board  11 . There is also another, different wire guide  19  fastened to the bottom center of board  11 . More particularly, each wire guide fits over one of the corner edges of board  11  before it is fastened to the underside of the board. 
     There is a piece of wire cable  16  that is passed around wire guides  15   a - 15   d  in the corners of board  11  and through wire guide  19  in an “X” pattern as shown in  FIG. 2 . This wire cable and its routing is part of the present invention. Initially, before being fastened into a closed loop, wire  26  is routed around each if the wire guides  15   a - 15   d  and through wire guide  19  in the “X” pattern shown in  FIG. 2 . 
     The two ends of wire  16  are shown fastened together and centered above wire guide  19  but they may off to one side of the wire guide. The two ends of wire  16  are then fastened to the two ends of a stretched spring  18 . To do this one end of wire  16  is attached to a first end of spring  18  using an eyelet (not shown). The other end of wire  16  also has an eyelet (not shown) attached thereto. Spring  18  is stretched approximately 1 inch beyond its un-stretched length and the eyelet attached to the other end of wire  16  is attached to the other end of spring  18 . More particularly, in  FIG. 2  the portion of wire  16  passing between the lower left corner of board  11  to the upper right corner of board member  11  passes through wire guide  19 . In this manner spring  18  does not contact the piece of wire  16  passing through wire guide  19 . 
     Wire  16  is positioned on and fastened to novel control elements  17   a  and  17   b  on the edges of board  11  as shown in  FIG. 2 . Control element  17   a  is mounted on the left edge of board  11  and control element  17   b  is mounted on the right edge of board  11 . This is shown in and described in greater detail with reference to  FIG. 3 . 
     In  FIG. 3  is shown a control element  17  and there is one ( 17   a ) mounted on the left side of board  11  and one ( 11   b ) mounted on the right side of board  11  as shown in  FIG. 1 . Element  17  has a wire capture screw  28  on its bottom, a brake knob  23  on its side and a top adjustment knob  26  on its top. All these screws and knobs are mounted on a side bracket  27  that has a “U” shape and is positioned sideways as shown to fit over an edge of board  11  as shown in  FIGS. 1 and 2 . Straightedge  25  has a slot in either end thereof and one of the two control elements  17   a  and  17   b  is mounted to each end of straightedge  25 . For both elements  17   a  and  17   b  the upper side of bracket  27  fits into the slot and knob  26  is tightened to firmly hold the top of side bracket  27  to the top side of straightedge  25 . There is a control element  17   a  and  17   b  attached to either end of straightedge  25 , as shown in  FIG. 1 , in this manner. 
     Brake knob  23  on the side edge of control element  17  has a knurled outer end that is turned by hand, and an inner end to which is affixed a brake pad  24  adjacent to board  11 . When straightedge  25  with control elements  17   a  and  17   b  attached thereto is mounted on a board  11  the side bracket  27  of both control elements are adjusted and tightened to have room for the two brake knobs  23  to be turned both in and out, and then the two top adjustment knobs  26  are locked. 
     To lock the loop of wire  16  to each control element  17  wire capture screw  28  is utilized. As shown in  FIG. 3  wire  16  is forced into a slot near the inner end of screw  28  where the wire is captured and tightly held. Wire  16  may also be attached to screw  28  in alternative ways. Straightedge  25  is carefully positioned on board  11  before wire  16  is fastened to wire capture screw  28 . When board  11  is in use the flat end of screw  28  rests against and rides along the bottom edge of board  11 . 
     Brake knob  23  is mounted through the side wall of side bracket  27  and on its inner end is a brake pad  24  that rests against the side wall of board  11 . More particularly, pad  24  of brake knob  23  of control element  17   a  rests against the left side of board  11  as seen in  FIG. 1 , and pad  24  of brake knob  23  of control element  17   b  rests against the right side of board  11 . 
     When straightedge  25  is located at a desired position on top of board  11  the left and right side brake knobs  23   a  and  23   b  are turned inward to push their brake pads  24  against the sides of board  11  and thereby lock straightedge  25  at the desired position on board  11 . When it is desired to move straightedge  25  up or down board  11  to a new position the two brake knobs are unscrewed a small amount to back off the brake pads  24  and thereby unlock the straightedge. Straightedge  25  is then slid up or down board  11  to a new position and the two brake knobs  23  are then turned inward to again push their brake pads  24  against the sides of board  11  and thereby lock straightedge  25  at the new position. 
     In  FIG. 4  is shown a snap lock  21  two of which,  21   a  and  21   b , are used to maintain the drafting board  10  in an upward inclined position, as shown in  FIG. 1 , when board  11  is in use. Rod  20  is formed into a rectangular loop as best shown in  FIG. 2 . Rod loop  20  is moved between a flat position against the bottom of board  11 , as shown in  FIG. 2 , when board  11  is not is use, and to an upright position, as shown in  FIG. 1 , when board  11  is to be used. 
     Looped rod  20  passes through the two snap locks  21   a  and  21   b  and as rod  20  is rotated between its flat position against the bottom off board  11  and its upright position extending away from board  11  it rotates approximately ninety degrees in snap locks  21   a  and  21   b . Snap locks  21   a  and  21   b  pinch rod  20  to lock it in whatever of the two positions selected by a user of drafting board  10 . The locking and unlocking is accomplished by locking levers  22 . The locked and unlocked position of locking levers  22  is shown in  FIG. 2 . 
     With the locking levers of  22   a  and  22   b  of the snap locks  21   a  and  21   b  in their unlock position looped rod  20  can be rotated within the two snap locks  21   a  and  21   b  between the position against board  11  ( FIG. 2 ) and extended away from board  11  ( FIG. 1 ). After handle  12  is moved to rotate looped rod  20  in snap locks  21   a  and  21   b  to extend its bottom end corners and feet  13   a  and  13   b  downward away from the bottom of board  11  locking levers  22   a  and  22   b  are moved as indicated in  FIG. 2 , as seen from the bottom of drafting board  10 , to clamp looped rod  20  where it passes through snap locks  21   a  and  21   b  and thereby lock looped rod  20  with its feet  13   a  and  13   b  in the downward position as shown in  FIG. 1 . 
     When it is desired to rotate looped rod  20  up against the bottom of board  11  to store the board, the locking levers  22   a  and  22   b  are moved as shown in  FIG. 2 , as seen from the bottom of board  11 , to unlock or unclamp looped wire rod  20  where it passes through snap locks  21   a  and  21   b . After looped rod  20  is rotated up against the bottom of board  11  using handle  12  the levers  22   a  and  22   b  are moved to the their lock position to again lock looped rod  20  in its up or retracted position against the bottom of board  11 . 
     In each of the four corners of board  11  is fastened a wire guide  15   a ,  15   b ,  15   c ,  15   d , each wire guide consisting of a plate with a small pulley attached thereto. The axis of the shaft on which the pulleys are mounted extends downward from and perpendicular to board  11 . There is also another, different wire guide  19  fastened to the bottom center of board  11 . More particularly, each wire guide fits over one of the corner edges of board  11  before it is fastened to the underside of the board. 
     What has been described herein is a preferred embodiment of the invention but those skilled in the art will recognize that numerous changes may be made without departing from the spirit and scope of the invention.