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5.11 Drawings issue form accompanying all drawings issued provides a convenient file record of such issues working on precarious scaffolding and battling against wind and rain should traditionally be expected to work from loose sheets of paper flapping round him.

It is appropriate that such bound manuals should contain the drawing register, and some form of guide to the drawing method.

Dealing with CAD drawings

File management

As has been noted in chapter 4, to talk of issuing CAD drawings is a misnomer. The drawing file itself is hidden away on a magnetic disk, and what in manual terms would be described as the drawn negative is in CAD terms a plot of the drawing, from which a negative must be printed in order that the necessary dyeline prints may be taken.

This is more than a matter of semantics. If a manually prepared negative should accidentally be destroyed the chances are that there is a print of it around the office from which it may either be re-drawn or re-constructed by photographic techniques. If the magnetic disk holding the drawings is destroyed or becomes lost within a filing system then it can never be reinstated, no matter how many negatives may exist in sheet form.

Two disciplines must therefore be observed to minimise the risk of such disasters, the first of which will involve copying the drawing on to a back-up disk at the end of each working session, and for the back-up disk to be stored away from the original. The second will occur when information carried on the working disk is transferred at the end of the project on to an archival disk, when the identification of each drawing file for retrieval purposes becomes of paramount importance. The archival disk will normally carry every drawing prepared within the office for that particular project, and it is essential that a comprehensive record be kept. The information indicated in 5.8 for recording manual drawings should in the main be sufficient for the purpose, but if copies of drawing files are to be issued outside the office as described below (and bear in mind that these will be the equivalent of negatives in manual draughting terms) then a more detailed and centralised record of what has been issued, to whom and at what stage, becomes imperative. It is furthermore highly desirable, if the system being used allows this, for the files to be 'locked' so that no additions may be made to them without the issuing office's knowledge and approval.

Transmission to other offices

Drawings produced by CAD may be transmitted electronically by the producing office to the site and other consultants, provided that the recipients are themselves equipped with computer and printer/plotter facilities compatible with those in the issuing office.

A draft of BS 1192 Part 5 (CAD Layering in the Construction Industry) was issued in 1992. Arising from comments made within the industry and its associated professions for the AutoCAD Users Group (AUG) proposed a structure for the necessary conventions. Work still remains to be done (in particular in developing ISO layer naming standards), but what has become known as the Layer Naming Convention for CAD in the Construction Industry, published by Autodesk, is in its present state a fully workable system.

It is based on the following layers of one or more digits:

Field 1: Discipline—ie Architect, Structural etc.

Identified by a single letter: A, S etc. Field 2: Category—ie the CI/SfB reference of the layer. For this 3 numbers are allocated (Table One numbers, usually with 0 at the end, but allowing the third digit to be used for more precise identification if so desired) Field 3: Graphics—ie items which are not specifically part of the drawn building-dimensions, text, hatching etc. Identified by a single letter Field 4: Grade—ie line thickness. The single figure code enables 9 different pen thicknesses to be identified

Field 5: Level—normally used for floor level, but since the code range is from 01 to 99 it is possible to use it also for identifying sections and elevations Field 6: Status—ie a single letter indicating whether the layer relates to new work, existing work, or work to be removed Field 7: Scale—an alphabetic identification of the scale at which the layer is intended to be reproduced. A single letter Field 8: Time—an alphanumeric identification of the phase shown on the particular layer. 1 number.

Thus the architect's 1:100 plan showing external openings at the second floor for Phase One of the project, using the thinnest line and with hatching incorporated in the drawing, would be layered:

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