US 3746992 A
A composite laminate planar structure including an upper layer of non-magnetic material and adapted to form the work surface of a drawing table, and a lower layer including a plurality of evenly arranged and elongated permanent magnets seated into corrugations of a corrugated sheet of high magnetical permeability to provide on said surface a plurality of spots of opposite polarity and capable of magnetically attracting ferrous strips superimposed to drawing paper sheet laid on and thus secured to said work surface.
Claims available in
Description (OCR text may contain errors)
United States Patent 1191 'Serembe A 1451 July 17,1973
[ MAGNETIC PLATE FOR DRAWING DESK LINING  Inventor: Ezio Serembe, 3 Viaie Corsica,
Milano, Italy  Filed: Sept. 15, 1971 ] Appl. No.: 180,655
 Foreign Application Priority Data Sept. 16, 1970 Italy 29793 A/70  US. Cl. 335/285, 33/107 R  Int. Cl. H01! 7/20  Field of Search 335/285, 302, 295,
[56 1 a Rem-mm Cited UNITED STATES PATENTS 2,958,019 l0/i960 Scholten et al. 335/285 3,518,593 6/1970 Hall 335/285 3,093,919 6/ 1963 Holt: 3,228,133 1/1966 Baermann 248/206 A X Primary Examiner-George Harris Attorney-Michael S. Striker  1 ABSTRACT A Composite laminate planar structure including an upper layer of non-magnetic material and adapted to form the work surface of a drawing table, and a lower layer including a plurality of evenly arranged and elongated permanent magnets seated into corrugations of a corrugated sheet of high magnetical permeability to provide on said surface a plurality of spots of opposite polarity and capable of magnetically attracting ferrous strips superimposed to drawing paper sheet laid on and thus secured to said work surface.
8 Claims, 6 Drawing Figures MAGNETIC PLATE FOR DRAWING DESK LINING BACKGROUND OF THE INVENTION This invention concerns a composite planar board or plate structure adapted to form the upper or work surface of a drawing board or the like and having pennanent magnetic properties adapted to provide magnetic attraction to ferrous components laid on said work surface, so that one or more sheets of drawing paper or other thin materials can be temporarily secured on said surface by partially superimposing strips of ferrous material to said sheet or sheets, said strips pressing the paper sheet on the drawing'board surface by being attracted by the magnetic board.
It is well known to the draftsmen that the securing of a sheet of drawing paper or drawing plastic sheet on a drawing board leads to certain problems. The use of conventional thumbtacks is objectionable, as they damage the drawing board surface and the drawing paper. The use of adhesive strips provides certain advantages in comparison with thumbtacks, but the problem cannot be said to be completely and satisfyingly solved, in particular when the unavoidable damaging of the drawing'board surface, upon repeated use, is taken into consideration.
Other problems are encountered when the draftsmans work requires a number of movements and positioning of paper sheets, for example when a number of details are to be copied in different positions, on transparent drawing paper, from an underlaid drawing, and
I It is therefore an object of this invention to provide a new and advantageous manner for temporarily securing paper sheets (this expression is to be considered in its broadest meaning, and-to encompass transparent or opaque drawing plastic sheeting, for example) on the upper or work surface of a drawing board, to be also intended in its broadest meaning encompassing any planar surface on which a draftsman or an artist can perform his activity, such manner being not subject to objections and disadvantages of the methods and means of prior art.
More particularly, it is object of this invention to provide a composite planar structure adapted to be secured to or to be simply superimposed on a suitable planar support, said structure having an upper smooth planar surface on which the draftsman can operate and embedding permanent magnet means and magnetically permeable components capable of exerting a substantial magnetical attraction on ferrous elements located on and in close proximity of said surface for pressing on said surface paper sheets or the like.
BRIEF SUMMARY OF THE INVENTION magnets, to provide on the said work surface a plurality of evenly arranged and closedly spaced spots of alternate opposite magnetic polarity, whereby a ferrous strip, superimposed on said work surface and bridging at least two adjacent spots of opposite polarity, can
close a magnetic circuit therebetween and be subject to a. substantial magnetic attraction urging said strip and a drawing paper located below said strip on said work surface.
These and other characteristics and features of the invention will be made evident to those skilled in the art from the following detailed description of a preferred embodiment of same invention, reference being made to the accompanying drawing.
THE VIEWS OF THE DRAWING FIG. 1 is a perspective diagrammatical view of a conventional drawing table provided with the magnetic lining of the invention;
FIG. 2 is a fragmentary perspective view of a part of the structure of the invention, applied upon a conventional planar upper structure of a drawing board;
FIG. 3 is a perspective exploded view of the fragmentary structure of FIG. 2;
FIG. 4 illustrates, in cross-sectional view and in greatly enlarged scale, a detail of the magnetic composite structure, the view including only one magnet and the parts adjacent thereto; I
FIG. 4A is a side elevation and partly a crosssectional view of a magnetic device adapted for advantageously complementing the invention; and
FIG. 5 is an exploded view of the detail shown in FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, wherein like reference numerals refer to like components and parts throughout the several FIGURES:
In FIG. 1 reference 10 generally indicates a conventional drawing table which, as to its general structure, does not form part of the invention. Such table can be of any known type and include either an adjustable or a stationary, either inclined or horizontalupper surface, generally indicated at 12, on which one or more drawing paper sheets, such as at 14, can be laid flat for drawing or designing thereon. The draftsmans work can be conventionally facilitated by suitable implements, such as an universal drawing device 16, for example, drawing rules and scales and so on, which during the drawing operation, are frequently displaced on the surface 12 and often caused to slide on the sheet or sheets 14, passing over the edges thereof. As known, in some occurrence, two or more sheets of paper must be superimposed to each other on the work surface 12. In FIG. 1 there are, for example, shown two paper sheets one of which partially spanning over another one. In such occurrences one or more sheets can require rather frequent relative positioning. By making use of conventional securing means, such as thumbtacks or adhesive ribbons, such means must therefore be frequently removed and then newly applied for securing the sheets in the different positions.
By improving the drawing desk with the lining of the invention, the paper sheet or sheets (such as those indicated at 14) can be very easily, surely and completely secured to the underlying work surface 12 by simply applying a suitable number of strips of ferrous material suitable to be attracted by a magnet on said sheet -or sheets. In FIG. 1 a number of such strips is shown and indicated at 18. Generally, it is convenient to apply the 1 strips along the edges of the sheets but, if desired or convenient, one or more strips may be positioned well within the contour of the sheets, in particular for maintaining flat large sheets of drawing paper, and/or when the sheets tend to roll-up, to bulge or anyway their planarity cannot be completely ensured.
It is evident that this latter possibility of securing a sheet on a drawing board, in one or more locations within its contour, without puncturing the sheet (an adhesive ribbon cannot be made use of in this occurrence) is an unique advantage provided by the invention.
A suitable number of such strips 18 can be provided as outfittings or equipment to complement the means of the invention. Such strips are obviously made of an iron-based material which can be magnetically attracted and thin enough for being of no or minor disturbance to the movements of the drawing implements. Preferably such strips 18 are made of mild steel, eventually chrome-plated, of thickness from 0.2 to 0.5 millimeter about and from 20 to 30 millimeters wide. To have a number of strips of varying lengths from 200 to 400 millimeters available is advantageous for meeting the most varying requirements of drafting operations.
As a matter of fact, such-thin strips are of not or of minor disturbance for the drawing implements movements. When the invention is used, the drawing rules and scales might havetheir lower faces very slightly rounded-off at their edges (as the draftsmen generally provide when making use of adhesive tape for securing the paper sheets), or provided with small rounded bulges or buttons to facilitate the passage of the implements over the very shallow steps provided by the thin strips 18.
Another unique advantage of the invention consists in that one or more drawing rules can be made of ferrous material or provided with a strip of ferrous material at their lower faces, so that such implements can be at their turn magnetically retained in position on the desk, for example for determining alignments.
It is evident that the magnetic planar structure of the invention must be such to provide an advantageous but not excessive attractive force upon the strips and eventually the drawing implements, so that such strips (and implements) can be readily detached from the work surface 12 by exerting a little manual effort thereon. It as been found as advantageous to provide permanently magnetical means asjusted to provide a force such that a pull of about 10 to grams/square centimeter will detach a strip as above, superimposed to a from 0.2 to 0.5 millimeter thick drawing paper or superimposed paper sheets.
According to the invention, the drawing desk is covered or lined with a magnetic plate preferably made as shown in FIGS. 2 to 5. Such plate comprise an upper layer generally indicated at 20, made of non-magnetic material and adapted to form a suitable drawing work surface at its upper face. This upper layer 20 is thin enough, such as from 0.5 to 0.8 millimeter, for providing a small spacing between the magnets, positioned therebelow, and the elements, such as the strips 18, which are to be magnetically coupled to said magnets. Preferably, such upper plate 20 consists of a commercially available drawing desk lining and consisting of two adhesively connected laminae, comprising an upper lamina 20a of plastic sheeting and of a lower lamina 20b of aluminum, the lining providing the necessary smooth and relatively hard work surface 12 for proper drawing thereon and engagement for the sharp points of compass and dividers.
The source of magnetical force is provided by the lower layer located below and adjacent to the lower face of said upper layer 20, and comprising permanent magnet means arranged to provide, on the said upper surface 12, a plurality of closely spaced spots of opposed magnetic polarity, such as diagrammatically indicated in FIG. 2 by ranges of symbols and According to an advantageous embodiment of the invention, the magnet means consists of parallel strips 22 of a ferrite containing composition, such as a commercially available rubber based magnetic composition. Such material is for example manufactured and sold, under the trade name SPROX by Magnetfabrik, of Bonn (West Germany). Such magnetic strips are advantageously from 1.5 to 3.0 millimeters thick and from 5 to 8 millimeters wide, and spaced by intervals not greater than twice their width; more close and even adjacent strips of such or equivalent material could be used also, the spacing or said strips being a compromise between cost and efficiency of the structure.
When spaced magnetic strips such as at 22 are provided, as shown in the drawing, each strip is seated into one recess of a plurality of recesses formed in an ondulated sheet of highly magnetically permeable material, the ondulations comprising flat portions both in the recesses and in the parts between the recesses, as shown in FIGS. 3 to 5 at 24. Tin-plated iron sheets from 0.3 to 0.6 millimeter thick can be made use of for forming the component 24. The raised flat portions of said component 24 are juxtaposed and secured, for example adhesively connected to the lower face of the said upper layer 20 to provide a composite but coherent and substantially rigid plate structure which can be in turn superimposed and connected to any conventional planar support, such as a wooden board 26.
The substantial rigidity of such structure is such that it can be made individually use of, by simply superimposing it on any suitable planar support, such as a writing desk, a table a bench and so on, for adapting it to draftsmans activity.
The strips 22 forming the magnets have opposite polarity at their opposite major faces, as diagrammatically shown in FIG. 5. The magnetical permeability of component 24, its shape and its arrangement relative to the magnet strips, provide for forming the desired alternated spots of opposite polarity on the upper work face 12. Such spots are closedly spaced enough that any strip 18, however positioned on said work surface 12, will bridge at least two oppositely polarized spots, thus closing a magnetic circuit therebetween and ensuring the desired attraction. An equivalent result can be obtained by providing permanently magnetized sheetings or strips having sposts of opposite polarity evenly and closedly located on its upper face. By making use of such latter materials, which also are available on trade, the component 24 can be omitted.
In consideration of the fact that some difficulties could be faced in manually removing the strips 18 from the work surface 12, because of the thinness of said strip, invention can advantageously complemented by the provision of one or more implements such as shown in FIG. 4A. Such implement comprise a small body 28 of insulating material, such a plastics, having an upper portion shaped for readily catching it between two draftsmans fingers, and a small flat permanent magnet,
such as a disk of ferrite 30, secured to its lower face. It is evident that such magnet 30 will be adapted for exerting on a strip 18 an attractive force greater than that exerted, on same strip laid on the work surface 12, by the magnets of the new structure whick forms the lining of said surface.
While the invention has been described and illustrated but in one preferred embodiment thereof, it is evident that several structural details might be modified for adapting best same invention to various requirement and conditions of service and/or to variously dimensioned and/or arranged drawing desks and boards. For example, vertical or nearly vertical drawing boards might require a somewhat greater attractive force. More powerful and/or more closed magnets can be made 'use of for example for large drawing desks for naval and aircraft draftsmen, where long flexible splines or strips must be exactly positioned and surely retained in position for drafting curved lines and so on, the new structure being unique for securing such elongated flewible drawing implements.
I claim: 1
1. A planar plate structure for use as a drafting board comprising an upper layer of non-magnetizable material andhaving an upper face adapted to form a work surface and a lower face; a plurality of spaced substantially parallel permanently magnetized strips having upper and lower surfaces of opposite'polarity arranged beneath said upper layer with said upper surfaces of said strips contacting the lower face of said upper layer; and a magnetically permeable element consisting of a ferrous undulated sheet forming shallow parallel grooves and raised ridges therebetween, said magnetized strips being respectively located in and substantially filling said grooves so that said ridges form portions of a polarity opposite to that of said upper faces of said magnetized strips, and said ridges being secured to said lower face of said upper layer to form with the latter a substantially rigid structure, whereby a ferrous element superimposed to said work surface and bridging portions of opposite polarity will be magnetically attracted against said work surface so that a paper or the like sandwiched between said element and said work surfaces will be securely held onto the latter.
2. The planar structure of claim 11, wherein said raised ridges have upper flat surface portions located in one plane with said upper surfaces of said magnetized strips. I
3. The magnetic plate structure of claim 1, wherein the said non-magnetizable upper layer is not more than 0.8 millimeter thick.
4. The magnetic plate structure of claim 3, wherein said upper layer is a laminated layer consisting of an upper lamina of plastic material and of a lower lamina of aluminum.
5. The magnetic plate structure of claim 1, wherein said magnetic strips are from 5 to 8 millimeters wide and from 1.5 to 3.0 millimeters thick, and spaced from each other not more than twice their width.
6. The magnetic plate structure of claim 5, wherein said magnetic strips consists of a rubbery composition including ferrite.
7. The magnetic plate structureof claim 1, and including ferrous strips from 20'to 30 millimeters wide and from 0.3 to 0.5 millimeter thick, adapted to be magnetically attracted on said work surface by a force of the order from 5 to l0 grams/square centimeter.
8. The magnetic plate strcture of claim 1, and including a manually operatable body of insulating material having a lower flat face, and a permanent magnet secured tosaid face, the said magnet being capable of magnetically attracting a ferrous element with a force greater than the force with which same element can be attracted on said work surface of the plate structure.