GB2073106A - Drafting apparatus - Google Patents

Abstract

A drafting kit includes (1) a flexible sheet 10 magnetized to have a large number of alternating N-S poles 12 extending in one direction and (2) a pair of straightedges 18, 24 which are magnetized so that one lines up parallel to the poles and the other perpendicular to the poles. By guiding a set square conventional, nonmagnetic triangle 30 along the straightedges, parallel, horizontal and perpendicular lines can be drawn without need for a T-square. The sheet, with straightedges and a drawing in place, may be stored either in roll form or against a suitable metal surface such as a file cabinet. <IMAGE>

Description

SPECIFICATION Magnetic drafting kit The magnetic drawing board of German patent application 2,902,668 of L. L. De Mathe has a rectangular wooden base to which is adhered a sheet of flexible permanent magnet material that has been magnetized to have a large number of alternating N-S poles of equal width which are parallel to the X-axis of the drawing board and extend the length of the sheet. Adhered to a drafting triangle are two pieces of identically magnetized permanent magnet material. One piece is arranged so that its magnet poles are parallel to one edge of the triangle and the other so that its poles are parallel to a perpendicular edge of the triangle. When the triangle is placed on the drawing board, the magnetic attraction aligns its perpendicular edges with the axes of the drawing board, thus eliminating the need for a T-square.However, because each piece of magnet material covers less than 50% of the area of the triangle, the triangle has a tendency to move slightly out of alignment when a writing instrument is pressed against an edge, especially at positions remote from the aligning piece.

Although one can slide the triangle to an infinite number of positions along the X-axis of the drafting board, the triangle moves in steps along the Y-axis. Hence, to draw lines along the X-axis, it is necessary also to use a conventional nonmagnetic triangle with its oblique edge resting against the oblique edge of the magnetized triangle.

The present invention concerns a magnetic drafting kit which avoids the aforementioned problems and has other advantages in comparison to the De Mathe drawing board. Briefly, the novel drafting kit comprises a broad, preferably rectangular sheet of flexible permanent magnet material which is magnetized in the same way as the magnetic material adhered to the De Mathe drawing board. That is, it is magnetized with alternating N-S poles of equal width extending substantially parallel to one axis of the rectangular sheet. The novel drafting kit also includes a pair of elongated straightedges of flexible permanent magnet material, each of which is magnetized to have alternating N-S poles identical to the poles of said rectangular sheet.One of said straightedges has one or two straight lengthwise edges parallel to its poles and the other has one or two straight lengthwise edges perpendicular to its poles.

The thicknesses of said broad magnet sheet and said straightedges are each greater than 0.25 mm and less than 1.5 mm.

The flexible magnet material preferably is sufficiently flexible to withstand being repeatedly wound around a 5-cm mandrel without cracking. Preferably the surfaces of both the rectangular sheet and the straightedges have tough, protective polymeric layers. The total thicknesses of the protective overlayer of the rectangular sheet and the protective underlayer of a straightedge should not exceed about 0.3 mm. The protective overlayer of the rectangular sheet preferably is provided by a preformed polymeric film which minimizes penetration by a compass point.

Suitable flexible permanent magnet material is conveniently manufactured as taught in U.S.

Patent No. 2,999,275 and is currently available in commerce in long rolls as wide as 60 cm. After the magnet material has been magnetized to have alternating N-S poles extending in a lengthwise direction and protective layers have been applied, this may be cut to any desired size. If the rectangular sheet has great length, one end may be temporarily rolled up while the draftsman works at the other end. The magnet attraction tends to prevent the rolled portion from unwinding accidentally. Even though of great length, the rectangular sheet of magnet material is conveniently stored in roll form and, if desired, with a drawing in place. Shorter lengths are conveniently stored by laying them against vertical metal surfaces such as desks, files and partitions and can be used in that position.

If desired, the rectangular sheet of magnet material can be permanently attached to a rigid substrate, such as the face of a briefcase so that one can use the briefcase as a portable drawing board.

Further advantages of the novel drafting kit will become apparent in connection with the drawing in which: FIGURE 1 is a schematic plan view of a drafting kit embodying the invention; and FIGURE 2 is a cross-section along lines 2-2 of FIGURE 1.

In the drawing, a broad rectangular sheet 10 includes flexible permanent magnet material 11 which is magnetized orthogonally to its broad surface to have at each broad face a large number of north and south poles which extend parallel to the X-axis of the sheet as indicated schematically in FIGURE 1 by broken lines 12. As seen in FIGURE 2, the alternating north and south poles are of equal width. Thin nonmagnetic protective layers 14 and 1 6 cover the broad faces of the magnet material 11.

A first elongated straightedge 1 8, which has a length-to-width ratio of about 10:1, is identical in construction to the broad rectangular sheet 10 and is magnetized in the same way. It has straight lengthwise edges 20 and 22 which are parallel to its magnetic poles. When the elongated straightedge 1 8 is laid on the broad sheet 10 in approximately the direction of the X-axis, the magnetic attraction virtually locks the straightedge in place against perpendicular movement, and it can be rather difficult to slide it along the X-axis.

A second elongated straightedge 24 is also identical to the rectangular sheet 10 in construction and magnetization. Is length-to-width ratio approximates 2:1 and its magnetic poles extend in its widthwise direction. It has straight lengthwise edges 26 and 28 which are perpendicular to its poles.

When the second straightedge 24 is laid against the broad sheet 10, the magnetic attraction virtually locks it into position as shown in FIGURE 1 of the drawing, and one can slide it along the X-axis only with difficulty.

Although the magnetic poles position the edges 20 and 26 of the two straight edges to be essentially perpendicular to each other, a conventional drafting triangle 30 should be used for fine adjustment. The edges 20 and 26 then serve to align the triangle 30 while still being thin enough to permit the triangle to be used while overlapping one of the straightedges 18 or 24 as shown in FIGURE 1.

Because the straightedges 1 8 and 24 are strongly attracted to the magnetic sheet 10 over their full areas, they can be used to secure a sheet of drawing paper 32, and there is no need to use drafting tape for this purpose. Conveniently, a base line is created by a thin, narrow strip of adhesive tape 34 to permit the drawing paper 32 to be aligned with the magnet poles of the magnet sheet 10. Preferably the thickness of the adhesive tape 34 approximates that of a typical drawing paper.

The straightedges 1 8 and 24 can be cut from the same roll of material as is the broad magnet sheet 10. However, in doing so, care should be taken to insure that each straight lengthwise edge of the straightedges is parallel or perpendicular to the magnetic poles. The length of one elongated straightedge 1 8 is preferably more than one-half the length of the X-axis of the magnet sheet 10 to provide a reasonable length of contact with a drafting triangle. Preferably its length-to-width ratio is at least 5:1 so as not to obscure an unnecessarily large area of the magnet sheet 10.

The length of the other elongated straightedge 24 is likewise preferably more than one-half the width of the magnet sheet 10 along its Y-axis. In the other direction, the straightedge 24 is preferably at least 5 cm in width in order to provide reasonably accurate positioning of its straight lengthwise edge or edges and to make it more resistant to being accidentally pushed out of alignment. A preferred range of length-to-width ratio is 2:1 to 5:1.

An optional accessory is a line-drawing guide 36 which is also identical in construction and magnetization to the broad rectangular sheet 10. It is relatively small as shown so that one can slide it easily along the X-axis of the rectangular sheet 10 by means of a writing instrument at its central opening 38.

Instead of the protective underlayer 16, there may be a pressure-sensitive adhesive layer covered by a removable, low-adhesion web. This would permit the magnet sheet 10 to be adhered permanently to a rigid board such as a pull-out shelf of a desk.

EXAMPLE The drafting kit of the present invention has proven to be very useful when constructed as follows: Magnet Material 11 Approximately 90 parts by weight domain-sized barium ferrite particles in 10 parts by weight of vulcanized rubber Thickness 0.75 mm Hc 1900 oersteds Br 2150 gauss By may 1.0 x 106 gauss-oersteds Width of each pole 2.3 mm Protective layer 14 Preformed plasticized vinyl polymer film having a decorative wood-grain pattern Thickness 0.13 mm Protective layer 16 Nylon polyamide coating applied from solution Thickness 0.13 mm First straightedge 18 3 x 30 cm Second straightedge 24 10 x 20 cm As compared to a conventional, nonmagnetic drawing board, the drafting kit of the present invention offers a number of advantages: 1. No T-square is required.

2. It can be easily rolled up for storage or to be transported in a briefcase.

3. Metal scales cling magnetically.

4. The magnetic straightedges hold drawing paper in position so it is unnecessary to use drafting tape.

5. The magnet sheet can be of virtually unlimited length of large drawings.

6. It is as convenient to use by a left-handed person as by one who is right-handed.

7. The thinness of the broad magnet sheet makes it easy to work at the edge.

Claims (9)

1. Drafting kit comprising a broad sheet of flexible permanent magnet material which is magnetized to have a large number of alternating N-S poles of equal width extending substantially parallel to one axis of the sheet, a pair of elongated straightedges of flexible permanent magnet sheet material, each of which is magnetized to have alternating N-S poles identical to poles of said broad sheet; one of said straightedges being elongated and having a straight lengthwise edge parallel to its poles and the other having a straight lengthwise edge perpendicular to its poles, each of said broad sheet and straightedges having a thickness of 0.25-1.5 mm.

2. Drafting kit as defined in claim 1 , wherein said broad magnet sheet is rectangular and its N-S poles extend parallel to the X-axis of the sheet, the length of said one straightedge exceeds one-half the length of the X-axis of the sheet, and the length of said other straightedge exceeds one-half the length of the Y-axis of the sheet.

3. Drafting kit as defined in claim 2, wherein said one straightedge has a length-to-width ratio of greater that 5:1 and said other straightedge has a length-to-width ratio of from 2 :1 to 5 :1.

4. Drafting kit as defined in claim 3, wherein the width of said other straightedge is at least 5 cm.

5. Drafting kit as defined in claim 1, wherein a thin, narrow strip of tape is permanently adhered to a face of the magnet sheet to extend parallel to the magnetic poles in order to facilitate the positioning of drawing paper on the magnet sheet.

6. Drafting kit as defined in claim 1, wherein a protective layer cover each broad surface of the broad magnet sheet and each of the straightedges.

7. Drafting kit as defined in claim 6, wherein the protective overlayer of the broad sheet is a preformed polymeric film which minimizes penetration by a compass point.

8. A drafting kit substantially as described herein with reference to the accompanying drawings.

9. A drafting kit substantially as described in the example herein.