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4.16 Recommended method of folding 'A' size sheets always keeps the title panel visible 84
4.17 (Left) Example of drawing title panel
We come now to the methods for producing the information which will ultimately be printed in negative form for final reproduction into multiple copies. There are two main methods in use, of differing degrees of sophistication, which may be categorised:
1. Manual draughting
2. Computer aided draughting.
This is the traditional method, carried out in ink or pencil on translucent paper or film secured to a drawing board or drawing machine. The resultant negative is then copied by one or other of the techniques previously discussed.
With manual draughting the creation of elementalised location plans is achieved by drawing the basic plan (see the section entitled 'the basic floor plan' in chapter 2) and taking from it the requisite number of copy negatives (normally by dyeline reproduction on some translucent medium which will take manual drawing on its top surface.) The elemental information is then added to each process negative, which is then coded elementally and printed as an opaque dyeline for inclusion in the drawing set.
The copy negative technique is really only applicable to location drawings. Even in situations where an assembly or component drawing has been given an elemental CI/SfB coded number it is unlikely to have benefited from the superimposition of two layers of information, and might as well have been produced as a single sheet, drawn once only.
Paper size is of less consequence here than in the other methods to be discussed, for the production of the negative is limited only by the size of the drawing board available, and the cost implications of using large drawings is not so great as they are with more sophisticated methods. Nevertheless, the same general comments regarding paper sizes which were made in the previous chapter still apply with manual draughting. No one is going to think kindly of you while trying to consult an AO sized drawing flapping about in a gale on an exposed building site.
As to the medium upon which manual drawing may be carried out, there is a wide enough range, coupled with a range of pens and pencils, to warrant being looked at in some detail.
This has the great advantage of being cheap and, because it offers a semi-opaque background, pleasant and satisfying to draw on, particularly in pencil. Against this must be set the fact that it is not an ideal medium for dyeline reproduction, giving insufficient contrast when compared with other media. If a lighter grade is used to improve its translucency (weights vary between 50 and 70 g/m2), then it becomes vulnerable to tearing and over-enthusiastic erasure.
Detail paper has its uses, but these are best limited to the preparation of drafts for subsequent tracing into final drawings, where the original sheet may be expected to have a limited life and where any prints taken from it will be for internal exchange of information among team members, and to rapidly-produced short-life pencil details (accompanying architect's instructions, for example).
It should not be used for drawings forming part of the original production set.
This, by far the most common medium to be found in drawing office use today, is available in a wide range of weights (from 50 to 112 g/m2) and surface textures (smooth, semi-matt and matt).
A smooth finish is desirable, especially for pencil work, where the more abrasive surfaces of the matt and semi-matt finishes tend to wear down pencil points rapidly, and are more difficult to keep clean during preparation of the drawing.
A weight of 90 g/m2 is probably the most common in general use in drawing offices, but it is arguable that 112 g/m2 paper justifies its extra cost. It is dimensionally more stable and less liable to go brittle with age. (Liability to buckling and dimensional instability through variations in humidity are two characteristics of all tracing papers.) It stands up better to heavy-handed erasing and it is less liable to damage than the lighter papers, a particularly important consideration in a large project which is going to be around for some years.
This has virtually superseded tracing cloth as a high quality product when durability is a prime requirement. It has other advantages which make it a contender, despite its high cost. It is dimensionally stable; it takes ink and pencil well; both may be erased easily. However, it is very hard on the normal technical pen, and it is desirable to use a range with specially hardened tips.
A major disadvantage in practical use is the fact that ink dries slowly, the film being totally non-absorbent and reliant upon evaporation alone for drying.
All in all, a good quality tracing paper offers the most practical all-round medium for general use.
Of the two available media for drawing lines the choice rests, to some extent, with the personal inclinations and particular abilities of the draughtsman. Many find pencil the more sympathetic medium, with its wide range of line inflexions, and a pencil drawing is normally a more personal document, reflective of the draughtsman's character, than the ink equivalent. The function of a working drawing, however, is the unambiguous conveyance of drawn information, and aesthetic considerations must remain secondary.
The relative advantages and disadvantages of both media are listed below, but on the whole considerations of permanence and reprographic clarity make ink the more suitable for the bulk of the final production set of drawings.
This is not to rule out the use of pencil altogether. Its speed, particularly when applied with self-confidence, makes it suitable for the production of large-scale details, full sizes of joinery sections, etc and supplementary details urgently needed on site. It is also useful as an adjunct to what are otherwise pen and ink drawings—for the addition of hatching, for example, which can be a time-consuming process in ink.
• Consistent density of line
• Reprographic clarity
• Permanence of image
• Completeness of erasure (by razor blade or mechanical eraser).
• Relatively slow process
• Set-square and scales liable to smudge still wet lines
• Erasure somewhat laborious.
• Speed of execution
• Wide range of line character
• Rapid erasure of errors and changes.
• Liability to smudging of completed lines
• Necessity for constant re-sharpening of pencil
• Difficulty of keeping sheet clean during preparation
• Difficulty of complete erasure.
Ink techniques: The old-fashioned adjustable ruling pen offered an infinite gradation of line thickness. Now that it has been superseded, for all practical purposes, by various systems of pens with interchangeable points of differing pre-determined thickness, the draughtsman is faced with the question of selecting from a very wide range of line thickness a limited number that may be used to give the appropriate degree of emphasis to different aspects of his drawing. It is clearly desirable to establish a convention whereby definable aspects of a drawing are always delineated at a given thickness, and in doing this it is likely that the line thickness requirements of such aspects will vary with the size, scale and function of the drawing.
Among the manufacturers of technical pens, there are two ranges of point thickness in common use. The earlier, and at the moment understandably the better established, offers the following line thicknesses: Range 1 (thickness of line in mm): 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0, 1.2.
The alternative is based on German DIN Standards and offers the following:
Range 2 (thickness of line in mm): 0.13, 0.18, 0.25,
Both ranges are shown at full size in 4.18.
Range 2 offers greater flexibility at the lower end of the scale, and the claim is made for it that it is better adapted for photographic enlargement or reduction of originals (when this is confined to the 'A' range of sheet sizes). It will be seen that each size in the range doubles the thickness alternately preceding it, with the result that alterations may be carried out to an enlarged or reduced copy negative in a similar weight of line to that appearing on the copy. (A similar facility is available in the Range 1 thicknesses by judicious selection.)
It is, of course, undesirable to mix the ranges on any given drawing. For 1:2 reduction of negatives the minimum recommended line thickness for use on the original drawing is 0.25 mm, allowing the use of the minimum size 0.13 pen for any alterations. In fact the general principle holds good, that in any process of reduction the minimum line thickness on the final print should not be less than 0.13 mm if legibility and uniformity of reproduction are to be maintained.
But for the normal production of working drawing negatives, where reproduction may be expected to be a 1:1 ratio, there is no reason why a thickness of 0.18 or 0.2 should not be selected for the thinnest line used.
Three different line thicknesses will suffice for most drawings. If we term them a, b and c, with a being the range one
Line thickness in mm range two
Line thickness in mm
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