Geometrical instruments – Straightedge type
Patent
1988-10-03
1990-06-19
Haroian, Harry N.
Geometrical instruments
Straightedge type
33DIG1, 33449, 33443, B43L 1302
Patent
active
049340611
DESCRIPTION:
BRIEF SUMMARY
This invention relates to draughting tables and drawing boards, to drawing instruments, and to analogous apparatus.
The making of engineering and manufacturing drawings is conventionally done by draughtsmen working with appropriate apparatus. The fundamental requirement is for a baseboard and means for attaching to that baseboard a sheet of paper, draughting film or the like on which the drawing is to be done. In much engineering drawing there is a requirement for extensive use of lines which run either horizontally or vertically and much need to draw lines accurately parallel or at right angles one to another. In order to facilitate drawing such lines, it is conventional practice to provide in association with such a draughting table appropriate apparatus, including some sort of mounted pair of rulers, one set at right angles to the other, and means for moving the pair accurately vertically and horizontally. One well known system consists of an upper track mounted along the top of the board in which a carriage slides. Mounted on that carriage is a vertical track generally running from top to bottom of the board, with a second carriage mounted in the vertical track. The second carriage can thus move up and down the board by sliding in the vertical track, while the whole assembly of second carriage and vertical traCk may be moved from side to side.
Mounted on the second carriage there is generally a pair of rulers set at right angles one to another. The pair may extend from a central member which is mounted pivotally on the second carriage, there being cooperating means on the pivotal member and second carriage to enable the rulers to be pivoted around an axis perpendicular to the surface of the board through a range of, e.g. 90.degree.. Locking means may be provided to enable the rulers to be locked at a particular orientation, and latch means may be provided to enable the rulers to be locked in a number of spaced predefined positions, e.g. either one vertical and the other horizontal or both at 45.degree. to the vertical and horizontal.
Such apparatus is widely used. Although it is very helpful for engineering drawings, it tends to be cumbersome in operation. It is also expensive to manufacture, particularly to the necessary high accuracy.
In terms of attaching the piece of paper or draughting film on to the drawing board, this is conventionally done using masking tape. However, in recent years it has become known to provide the surface of the board with a permanently magnetised material and to hold a sheet of paper or the like down by the use of magnetic strips (usually flat strips of stainless steel) which sandwich the paper or draughting film between themselves and the board.
Another approach to drawing by hand a set of parallel lines, e.g. for cross hatching or the like, is to use a drawing instrument referred to as a "parallel rolling rule". This consists of a ruler having set adjacent its ends a pair of rollers. The axis of each roller is parallel to the ruler edge, and the rollers are so positioned that when the ruler is rested on a drawing surface, it may be moved in a direction perpendicular to the edge by rolling it on the rollers. Such rulers are of particular value in drawing parallel lines on navigational charts, being generally easier to use than a pair of standard parallel rules (two rules connected together by means of two pivotal identical length stays thus forming a parallelogram). Such rulers are, however, only as good as their user in terms of the ability to draw a set of parallel lines, and in particular slippage can occur of one end relative to the other.
British Patent Specifications Nos. 2015756A and 2073106A disclose draughting apparatus using a stripwise magnetised drawing surface in conjunction with a magnetised member such as a set-square; such apparatus is inflexible in use, though parallel lines can be drawn with it.
We have now found that by the use of particular magnetic apparatus, substantial improvements in drawing and draughting boards, and in drawing instruments for use
REFERENCES:
patent: 1406061 (1922-02-01), Muller
patent: 2360911 (1944-10-01), Tress
patent: 3618137 (1971-11-01), Bassett
patent: 3672062 (1972-06-01), Baker
patent: 3866326 (1975-02-01), Hebel
Frazer Stephen O.
Knight Jonathan
Riddiford Martin
Breiner A. W.
Haroian Harry N.
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