US3137089A - Drawing board - Google Patents

Description

A. J. SMITH ll DRAWING BOARD June 16, 1964 2 Sheets-Sheet 1 Filed March 22, 1965 INVENTOR. Azmv J1 5M/TH,JI BY '47TORNEY A. J. SMITH ll June 16, 1964 DRAWING BOARD 2 Sheets-Sheet 2 Filed March 22, 1963 INVENTOR ,4/.L- JT SM/TH, H BY A/ V of a rectangular configuration.

3,137,089 DRAWENG BOARD Allen J. Smith ll, Wyndham Drive, York, Pa. Filed Mar. 22, 1963, Ser. No. 267,256 6 Claims. ill. 45-431) This invention relates to improvements in the structure of a drawing board and, more particularly, but without restriction thereto, in a drawing board of the type'intended to be attached to supporting means, such as a 4-post or pedestal arrangement.

For many years, it has been customary in the manufacture of drawing boards to select solid wooden boards or planks, carefully planing opposite surfaces and the edges longitudinally, and arranging a plurality of the same in edge-abutting relationship, sometimes using tongue and groove construction and/or cementing the edges together. In some instances, relatively narrow boards have been used, whereby a substantial number of such narrow boards havetbeen connected together to form a composite board of desired area, it being the theory that theoverall warpage of such a composite drawing board made from such narrow boards would be less than the warpage of a drawing board assembled from wider boards. In most drawing boards of this type, battens were aifixed either to the rear surface or along the ends of the boards across the grain thereof; and screws, slotted grooves or other mechanical means were employed to connect the battens to the board.

- Composite drawing boards of the type referred to above employing end type battens, which were disposed in the same plane as the boards comprising the composite drawing board, frequently connected the battens to the composite board by means of a tongue and groove construction. Such end battens served as guide rails for T-squares and other similar straight-edge constructions.

rangements thereover.

Bracing of the type referred to above adds structural bending strength to the board onlyacross the grain, which, in most board constructions, is across the shorter dimension of the board, inasmuch as drawing boards are usually Such bracing, however, has presented problems due to the inherent nature of wood. Wood is of a cellular nature, the cells being elongated and extending parallel to the direction of the socalled grain of the wood. Accordingly, when wood is cut transversely to-the grain, many more cell walls are cut through than when wood is cut parallel to the grain. The

are to be prevented.

When attaching battens to wooden composite drawing boards, such as by applying the same against the rear surface of the board with screws, either enlarged holes,

United States Patent "ice slots of limited length, or other similar accommodations for the screw should be utilized in order to permit the screws to move relative to the battens-as a result of the expansion and contraction of the composite board assembly. Hence, such slotted attachments cannot be firmly fixed. Unless limited movement of this type is provided between the board and the battens, climatic changes will result either in the board warping, or in the threaded engagement between the screws and the board enlarging, the screws bending or other undesirable conditions resulting.

Particularly when metal battens are secured to the rear surface of a wooden composite board, if no provision for expansion or contraction of the wooden boards is made, such as slots in the metal battens, it has been found that screws near the center of the board will remain intact, while screws closer to the outer edges of the board will either be bent, or the expansion and contraction of the boards will cause slot-like holes to be formed in the boards by the screws, said openings being longer adjacent to the outer ends of the battens than nearer the centers thereof.

A further disadvantage of conventional drawing boards is that there normally is no convenient place to store, or temporarily dispose, the various tools, pencils, scales, etc., used by draftsmen, other than by providing a somewhat simple strip which extends along the bottom edge of the board and serves as a stop to prevent tools, and the like, from sliding off the board surface. Draftsmen frequently resort to various makeshift storage arrangements, such as taping small boxes, etc., to the T-squares, straight-edges and drafting machines which are used on drawing boards. A storage trough for tools and instruments is useful, but has the disadvantage, particularly in regard to large drawings, ofacting as a spacer between the draftsman and his work.

With the advent of track-type drafting machines comprising a guide bar extending along the upper edge of the drawing board and fixed thereto so as to be straight and parallel to said upper edge, to provide a guide track for e the vertical guide bars of the drafting machine and along whichthe drafting scales move toward and from the top guide bar, it has been found that a certain amount of socalled dead space occurs at the left-hand side of the drawing board when the drafting machine is a so-called righthand machine. This is caused by the'fact that the track at the top of the board usually does not extend beyond the left end of the board, and acertain portion of the length of said track is subtended by the slidable bearing construction connected to the upper ends of the vertical guide bars. Thus, an area of anywhere from 8 to 12" in a horizontal direction and extending for the full width of the board in a direction transverse to the top and bottom edges of the board is occupied by the vertical guide bars of the drafting machine when the machine is moved to its fullest extent toward the left end of the board, and

' weight drawing board having relatively thin cover sheets forming the opposite surfaces of the board, such cover sheets being made of similar material and similarly finished, and means to connect the cover sheets to maintain the same inuniformly spaced relationship to each other and also provide certain parts of the spacing means to whihc supporting mechanisrnof various kinds may be connected to the board firmly and effectively, without inducing any tendencies for the board to warp due to atmospheric conditions, or otherwise.

A further object of the invention comprising an adjunct to the foregoing object is to provide lightweight but effective cellular or grid-like means which extend between the cover sheets of the board so as to prevent movement thereof relative to each other, and still further, the compartments defined by the cellular construction preferably are provided with vent openings to permit the entrance of the external atmosphere, thus providing means which per- -mit the equalization of changes in exterior vapor pressure within the interior of the board, whereby the board has ventilating means associated with all internal compartments of the board.

Stillanother object of the invention is to form a recess of substantial area adjacent to the left end of the board, said recess coinciding with the vertical track bar arrangement of a track-type drafting machine when moved to its farthest position adjacent to the left end of the board and, in the preferred construction thereof, said recess is provided with partitions or shelf-like constructions arranged for purposes of holding draftsmens tools or accessories, small models, or the like, in convenient location for access to the draftsman.

Details of the foregoing objects and of the invention, as well as other objects thereof, are set forth in the following specification and illustrated in the accompanying drawings comprising a part thereof.

In the drawings:

FIG. 1 is a front view of a drawing board embodying the principles of the present invention and illustrated with an exemplary track-type drafting machine attached thereto and supported by pedestal means affixed to the rear surface of the board.

FIG. 2 is a plan view of the drawing board shown in FIG. 1 with the upper cover sheet removed to expose to view the preferred type of internal construction provided in the board.

FIG. 3 is a fragmentary, perspective view showing in greater detail than FIG. 2 the grid-like spacing means shown in exemplary manner in FIG. 2 and illustrating certain details of the venting arrangement.

FIGS. 4 and 5 respectively are fragmentary, sectional views taken on the lines 44 and 55 of FIG. 2 to show details of preferred constructions.

FIG. 6 is a rear view of the board shown in FIG. 1, but illustrated on somewhat larger scale and illustrating one form of attaching means by which the board may be secured to a supporting pedestal, or the like.

FIG. 7 is an end view of the board construction shown in FIG. 6 and illustrating different positions of adjustment of the board relative to this supporting pedestal.

FIG. 8 is a longitudinal, sectional view through a fragmentary portion of the board to illustrate the venting arrangements.

FIG. 9 is an end view of a fragmentary portion of the board, as seen on the line 9--9 of FIG. 8.

FIG. 10 is a side elevation of another embodiment of supporting means for the board other than that shown in FIGS. 6 and 7.

The drawing board 10, which comprises the present invention, essentially is of sandwich construction and consists of a pair of cover sheets or skins 12 and 14, which are separated by spacing means 16. The cover sheetslZ and 14 are of identical construction and composition. One highly suitable material for such cover sheets comprises relatively thin plywood of at least three plies. Plywood formed from maple or birch especially is suitable, since this type of plywood is'of the hardwood variety and provides durable working surfaces when finished.

Three-ply plywood having a total thickness, for example, of approximately is very appropriate and readily available. Various types of tempered composition hardboards, however, are suitable for use as such cover sheets or skins, one commercial type being sold under the trade name Masonite. This material is less expensive than hardwood type plywood, but is of greater weight. Softwood plywoods of different types also may be used and, while less costly, also afford less strength. Regardless of the material selected and used, however, smooth sealer finishes preferably are applied similarly to both of the cover sheets, particularly for purposes of protecting the material from both soil and sudden climatic changes.

The spacing means 16 comprise wooden blocks which all are of the same thickness. Elongated frame blocks 18 and 20 respectively are positioned adjacent to the top and bottom of the board 10, and end blocks 22 and 24 extend between the opposite ends of the top and bottom blocks 18 and 2t) and appropriately are connected thereto by joint constructions, dowels, and/or gluing.

The perimeter of the frame comprising the connected blocks 18, 2t 22 and 24 is coextensive with the edges of the cover sheets 12 and 14, and said cover sheets are glued to said frame While held under pressure, so as to provide effective bonding between such spacing frame and the cover sheets.

It will be seen, especially from FIG. 2, that the frame members are of appreciable width. In practice, this width is of the order of between 2" and 3", whereas the preferred overall thickness of the board, including the cover sheets, is between 1 /8 and 1%. Thinner or thicker boards are possible within the purview of the invention, but the limits indicated above are average for most commercial type drawing boards.

In view of the fact that even though the cover sheets 12 and 14 are of a rigid nature, and especially when formed from hardwood type plywood of /s thickness, or the like, such thickness of plywood, or other similarly dimensioned appropriate cover sheets, would not be adequate to maintain a rigid, flat working surface, under most circumstances, especially in view of the fact that it is not uncommon for draftsmen to lean rather heavily upon the surface of drawing boards during the performance of their duties. Accordingly, the spacing means comprising the present invention also includes the use of other members, such as additional wooden blocks 26 and 28, which extend transversely between the top and bottom blocks 18 and 20. The opposite ends of the additional blocks 26 and 28 are securely fastened to said top and bottom blocks by any suitable means, such as those employed to connect the end blocks 22 and 24 to said top and bottom blocks.

It will be understood that in regard to the blocks 22, 24, 26 and 28, the grain thereof extends lengthwise of the blocks and transverse to the grain in the top and bottom blocks 18 and 20. There also is an additional wooden block 30 of similar length to theblocks 26 and 28 and interposed between the end block 22 and the additional block 26, as shown in FIG. 2, the ends of the block 30 likewise being afiixed to the top and bottom blocks 18 and 20 by the same means as employed to secure the other trans verse blocks thereto.

The additional block 30 and end block 22 define the opposite sides of a cavity 32, which is for purposes to be described. It also is to be understood that all of the wooden blocks thus far described are of the same thickness and of the same material, clear grained white pine being preferred, although the invention is not restricted to the use of this specific type of wood.

In some constructions of drawing boards, in accordance with the invention, it is desired also that a further wooden block 34 be disposed substantially in parallel relationship to the top and bottom blocks 18 and 20 and interposed therebetween, the block 34 fitting between the additional blocks 26 and 28, as shown in FIG. 2, and being of similar material and similar thickness. It is preferred that the ends of block 34 are not secured to the blocks 26 and.

28, but, nevertheless, are held in operative position relative thereto at least by the skin sheets 12 and 14 being glued thereto.

While the use of the various additional and further blocks 26, 28, 30 and 34 aifords a certain amount of reinforcement to the rigidity of the cover sheets 12 and 14,

. especially for purposes of preventing the movement of the cover sheets toward each other, the invention also, in its preferred construction, makes use of additional grid-like spacing means 36, details of which are best shown in FIG. 3. This grid-like, reticulated construction comprises transversely arranged wooden strips 38 and 40, which are relatively thin, such as of the order of A2 or 7 and the Width thereof is commensurate withthe thickness of the various wooden blocks between which the various sections of spacing means 36 are disposed.

The strips 38 and 40 are provided with half-together joints, which is an arrangement commonly used in egg carton spacers. The ends of the strips 38 and 40 are securely fastened to the inner surfaces of the various frame members and other additional blocks comprising the principal other elements of the spacing means for the cover sheets. If desired, the ends of the strips 38 and 40 may even be mortised into the inner surfaces of the frame members and additional blocks.

It thus .will be seen that the grid-like spacing means 36, especially when the strips thereof are arranged to be about 2" apart in transverse directions, will provide a plurality of cells, and the closely disposed spacing elements comprising the strips 38 and 40 will afford uniformly dispersed overall support'for the various areas of the cover sheets 12 and 14'between the frame members and" other additional blocks 26 and 28 of the drawing board. This arrangement thereby affords very extensive support, at restricted locations, on the cover sheets. Glue is applied to the opposite edges of the strips 38 and 40 comprising the gridlike means 36 so as to securely anchor the cover sheets to such spacing means, thereby further aiding in stiffening the entire board and thus. preventing bending thereof. Especially from visualizing the configuration shown in FIG. 2, it also will be seen that the cover'sheets 12 and 14 are secured to the various elements comprising the spacing means between the cover sheets at a minor portion of the total area of said sheets.

The cover sheets selected for connection to the spacing means therebetween are of a sufiiciently rigid nature, as well as being able to sustain compressive and tensile stresses, whereby when the cover sheets are secured to the various spacing means, a truss-like effect is produced throughout the entire composite drawing board in that, when pressure is applied against the top of the board, the topcover sheet will sustain compression, whereas the bottom cover sheet will sustain tension, and the spacing means between will prevent relative movement of the cover sheets toward each other. Accordingly, considering particularly the relatively light weight of the board to time, comprises the ventilating eifectincorporated into the board. Details of the construction providing this effeet are best shownin FIGS. 3, 8 and' 9, wherein it will be .seen that cells 42 between the intersecting strips 38 and I 40 of thegrid 36 can communicate with the'exterior atmosphere the employment of'slots or grooves 44 formed in the various wooden blocks of the spacing means 16, including those blocks comprising the frame, as well as the aforementioned additional blocks. The slots or grooves 44 preferably are provided in opposite surfaces of said wooden blocks, in staggered relationship, as best shown at the righthand end of FIG. 8, whereby the opposite surfaces of the blocks will be similar and thereby eliminate a possibility of warpage.

In addition to the slots or grooves 44 formed in the various blocks of the spacing means 16, the strips 38 and 40, per se, of the grid construction 36 likewise are provided with small notches 46, in staggered relationship in the opposite edges thereof, for purposes of providing intercommunication between the various cells 42 of the grid means 36 and, ultimately, with the exterior atmosphere through the'medium of the slots or grooves44. Thus, equalization of changes in exterior vapor pressure within the interior of the board is permitted through the ventilating means described above.

In addition to affording stability to the cellular type drawing board 10, especially by providing cross struts in the generally rectangular frame comprising top and bottom blocks 18 and 20 and the end blocks 22 and 24, the

additional blocks 26 and 28 comprise means to which appropriate brackets, or other type of attaching means, may be connected firmly for purposes of enabling the board to be supported by an appropriate pedestal 48, or the like. It is to be understood that the pedestal48 is merely exemplary and illustrative, and various other types of supporting devices having central connecting means for attachment to the board 10 may be utilized. In the exemplary illustration of attachment bracket shown in FIG. 6, the bracket preferably is H-shaped and comprises batten-like members 50, which are parallel to each other, and any suitable transverse means, such as a channel member 52, extends therebetween and is connected at its ends rigidly, such as by welding, to the members 50. Preferably, such bracket elements are metallic.

Exemplary connecting ears 54 may be connected to e an uppermost bearing member 56 on the upper terminal end of a vertically adjustable post SSextending from the upper end of pedestal 48, and any suitable clamping means for holding angular adjustment of the board 18 relative to the post 58 may be employed. Threaded or camsmeans, for example, not shown in detail, and not comprising a novel part of the present invention, are suitable, and particularly those types which might be operated by an actuating handle 60, which is within ready access adjacent to the bottom edge of the board 10. In FIG. 7, several exemplary positions of the board relative to post 58 are shown, respectively, in full and broken line.

Considering FIG. 6 particularly, and especially considering the fact that wooden blocks expand transversely due to moisture changes, if the battens 50 are secured to the rear surface of theboard substantially midway between the opposite edges of the additional wooden blocks 26 and 28, expansion from the centers of each of said blocks equally in opposite directions can be expected, whereby there will be no expansion of any consequence between the central portions'ofthe two blocks 26 and 28 with respect to each other. The fact that block 34 preferably is not connected to blocks 26 and 28 facilitates such small expansion and contraction of blocks 26 and 28. When the bracket comprising members 5!) and 52 are formed from metal and are connected to each other integrally, no appreciable expansion will take place, even due to extreme temperature changes, whereby no warp age of the board will occur, as a result of such supporting mechanism. Further, the channel member 52 may be secured by screws or the like to the further wooden block member 34, which extends between the additional blocks 26 and 23. Also, said further block 34 may be used in other capacities for purposes of connecting supporting means thereto, either singly or in conjunction with the.

blocks 26 and 28. To secure battens 50 to blocks 26 and 23, rows of screws are employed, said rows being parallel to the direction of the grain of blocks 26 and 28;

. The relatively substantial bottom wooden block 20, comprising a longitudinally extending frame member, also is ofadequate size and capacity to permit the use of hinges 62 to be connected thereto, preferably'at longi tudinally spaced locations, an exemplary end view of such hinge arrangement being shown in FIG. 10. The hinges 62 otherwise may be secured to table-type supporting means 64 and a bracket do is connected, for example, to block 34 within the board by screws with a bracket 50, 52, shown in FIG. 6, including ears 54, if desired, for purposes of pivotally connecting an adjustable brace or prop 63 to the underside of the board 10.

The lower end of the prop 68 may engage serrated, notched, or clamping positioning means 7%}. In lieu of using a single prop 68, if desired, a pair of props 68 might be connected to the reverse or underside of the board, the blocks 26 and 28 comprising suitable locations to which appropriate brackets may be connected. The end blocks 22 and 2,4 of the frame also may be used for connecting brackets for the plurality of props 6S thereto. Under such latter circumstances, each prop would have a separate positioning means 719 connected to the table-type supporting means 64.

Referring to FIGS. 2 and 5, it will be seen that the top frame block 18, on its reverse side, and adjacent to the upper edge thereof, is provided with a longitudinal channel '72 for purposes of receiving a supporting strip 74 secured thereto by screws and having spaced sockets 75 to receive supporting screws 76 to which bar track 86 is secured to slidably support head 78 of a track-type drafting machine illustrated in exemplary manner in FIG. 1. The machine 78 has a vertical track assembly consisting of vertical guide bars 82 and 84, as best shown in FIG. 1, the bar 82 being perpendicular to the track 80 and slidably supporting the guide sleeve 86, which supports the adjustable protractor head 83 of the machine, while a counterweight 9%) slides along the bar 84 in opposition to the guide sleeve 86. The guide sleeve 86 and counterweight fitl are connected by cable 92.

The principal purpose for illustrating the details of the track-type drafting machine 78 is to explain the condition that, when the horizontally traveling vertical guide bars 82 and 84 are moved to the left end of the board, as viewed in FIG. 1, there is a relatively substantial area at the left-hand end of the board it which is beneath the spaced bar arrangement 82 and 84- of the drafting machine and therefore is useless, from a practical standpoint, for drafting purposes. In accordance with the principles of the invention, this useless area is adapted for utilitarian purposes, by making the interior cavity 32 of the board, between the blocks 22 and 36, as seen in FIG. 2, available for the following purpose.

It is characteristic of the track-type drafting machine 78 that the counterweight bracing bar 84 extends downward and inward at the bottom toward the perpendicular guide bar 82 for the drafting head sleeve 86, particularly for triangulated reinforcement. Particularly for esthetic and space conservation purposes, the left-hand edge surface 94 of the board 10 is arranged at an angle to the top and bottom edges of the board, similar to that in which the bracing bar 84 extends, such angular arrange ment of the edge 94 being shown best in FIGS. 1 and 2. Simply by cutting a hole 96 in the cover sheet 12 of the board, so as to be complementary to the hollow cavity 32 formed between wooden blocks 22 and 36 on the interior of the board, as shown in FIG. 2, the entire space 32 is rendered available for the useful purpose of placing suitable retaining means, such as shelf-like partitions therein.

As is preferred in accordance with the present invention, a formed or fabricated metal or plastic tray 98 is constructed so as to be complementary to the outline of the cavity 32, the bottom wall of which cavity is defined by the cover sheet 14 on the reverse side of the board 10, as is clearly shown in FIG. 4. The tray 98 preferably is outline by a peripheral flange 105 which closely overlies the upper surface of the cover sheet 12 of the board. The tray 98 also preferably is provided with a plurality of transverse webs or ribs 102, which define compartments of various sizes within the tray and shelf-like supporting means to retain drafting implements and supplies, models, or the like, within position for ready access by the draftsman, especially when the board is disposed at an acute angle to the vertical, such as shown in broken lines in FIG. 7, for example, or as illustrated in FIG. 10. Even when the drafting machine 78 is disposed in its farthest possible position adjacent to the end of the board which contains the tray 98, access to the tray is obtainable through the space between the bars 82 and 84 of the frame.

It will be understood that if the drafting machine 78 is of the right-hand type, whereby the drafting head 88 extends toward the left therefrom, then the compartment 32 and the tray 98 disposed therein would be positioned at the right-hand end of the board 10.

While the invention has been described and illustrated in its several preferredembodiments, it should be understood that the invention is not to be limited to the precise details herein illustrated and described, since the same may be carried out in other ways falling within the scope of the invention as claimed.

I claim:

1. A drawing board comprising a substantially rectangular frame of top and bottom solid wooden elongated beam-like blocks of uniform thickness connected at the opposite ends by end blocks of the same thickness and limited width to form a closed frame enclosing an inner area substantially greater than the area of said blocks, rigid cover sheets of similar plywood of at least 3 plies extending across the opposite surfaces of said frame and securely afiixed thereto adjacent the edges thereof, said plywood cover sheets being substantially coextensive in area with said frame and thinner than said frame and being finished similarly on the exterior surfaces thereof, additional wooden blocks of equal thickness to those forming said frame and extending transversely between said top and bottom blocks of said frame and fastened at their ends thereto, said additional blocks being wider than said end blocks of said frame and spaced from each other longitudinally of said frame and substantially evenly inward from the opposite ends of said frame to brace said frame and provide means for the attachment of supporting means to said board, and wooden spacing means of equal thickness to said frame positioned within said frame between said cover sheets and fixed thereto at spaced locations of restricted area generally throughout the full extent of at least the central portion of said board to prevent movement of said cover sheets toward each other and provide a lightweight drafting board which is substantially insusceptible to warping.

2. The drawing board set forth in claim 1 further including a further wooden block or equal thickness to those forming said frame and extending transversely between said additional wooden blocks intermediately of the ends thereof and fixed at the ends thereof to said additional wooden blocks to provide additional bracing for said board.

3. The drawing board set forth in claim 1 further characterized by said additional wooden blocks being parallel to each other and the grain thereof extending lengthwise to receive securing means such as a row of screws lengthwise of said grain of said blocks for attaching supporting or positioning means to said drawing board.

4. The drawing board set forth in claim 3 further characterized by said wooden spacing means between said cover sheets comprising thin strips arranged in gridlike formation to provide a reticulated supporting means for the cover sheets to prevent sagging movement thereof when pressure is applied against the exterior of said sheets, said reticulated supporting means being disposed substantially uniformly within substantially all the spaces between the frame blocks and said additional wooden blocks. I

5. The drawing board set forth in claim I further characterized by said board adjacent one side thereof having a holecut in one of said cover sheets inwardly from one end thereof and extending transversely between the top and bottom of said board to define a recess in the board, the bottom of said recess being defined by the opposite cover sheet of said board, and a shallow receptacle having sides complementary in shape to said hole in said one cover sheet removably positioned therein to receive and retain various articles conveniently for use by a draftsman.

6. The drawing board set forth in claim 5 provided 7 with attaching means spaced along and connected to the ing transversely spaced vertical track bars overlying the board when in use and the shape of the area outlined by said spaced vertical track bars being complementary to the shape of said receptacle and said bars overlying the same when such drafting machine is disposed in its endmost position adjacent the end of the board containing said receptacle, whereby said receptacle only occupies space which is unusable for drafting purposes.

References Cited in the file of this patent UNITED STATES PATENTS Pasquier June 30, 1942

Claims (1)

1. A DRAWING BOARD COMPRISING A SUBSTANTIALLY RECTANGULAR FRAME OF TOP AND BOTTOM SOLID WOODEN ELONGATED BEAM-LIKE BLOCKS OF UNIFORM THICKNESS CONNECTED AT THE OPPOSITE ENDS BY END BLOCKS OF THE SAME THICKNESS AND LIMITED WIDTH TO FORM A CLOSED FRAME ENCLOSING AN INNER AREA SUBSTANTIALLY GREATER THAN THE AREA OF SAID BLOCKS, RIGID COVER SHEETS OF SIMILAR PLYWOOD OF AT LEAST 3 PLIES EXTENDING ACROSS THE OPPOSITE SURFACES OF SAID FRAME AND SECURELY AFFIXED THERETO ADJACENT THE EDGES THEREOF, SAID PLYWOOD COVER SHEETS BEING SUBSTANTIALLY COEXTENSIVE IN AREA WITH SAID FRAME AND THINNER THAN SAID FRAME AND BEING FINISHED SIMILARLY ON THE EXTERIOR SURFACES THEREOF, ADDITIONAL WOODEN BLOCKS OF EQUAL THICKNESS TO THOSE FORMING SAID FRAME AND EXTENDING TRANSVERSELY BETWEEN SAID TOP AND BOTTOM BLOCKS OF SAID FRAME AND FASTENED AT THEIR ENDS THERETO, SAID ADDITIONAL BLOCKS BEING WIDER THAN SAID END BLOCKS OF SAID FRAME AND SPACED FROM EACH OTHER LONGITUDINALLY OF SAID FRAME AND SUBSTANTIALLY EVENLY INWARD FROM THE OPPOSITE ENDS OF SAID FRAME TO BRACE SAID FRAME AND PROVIDE MEANS FOR THE ATTACHMENT OF SUPPORTING MEANS TO SAID BOARD, AND WOODEN SPACING MEANS OF EQUAL THICKNESS TO SAID FRAME POSITIONED WITHIN SAID FRAME BETWEEN SAID COVER SHEETS AND FIXED THERETO AT SPACED LOCATIONS OF RESTRICTED AREA GENERALLY THROUGHOUT THE FULL EXTENT OF AT LEAST THE CENTRAL PORTION OF SAID BOARD TO PREVENT MOVEMENT OF SAID COVER SHEETS TOWARD EACH OTHER AND PROVIDE A LIGHTWEIGHT DRAFTING BOARD WHICH IS SUBSTANTIALLY INSUSCEPTIBLE TO WARPING.

Images