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4.11 Component destined to fill the opening shown in 4.10 is also defined by its co-ordinating dimension

It will be prudent to note in the drawing set that this method has been adopted. A note on the component schedule or component drawings stating that 'Dimensions given for components are co-ordinating dimensions. The manufacturer is to make his own reductions to give the work size of the component.' should avoid the possibility of error.

Definitions

It may be helpful at this point to summarise some of the terms referred to into a list of definitions and to add to them others in common use:

Co-ordinating plane Line representing the hypothetical boundary between two adjoining building elements.

Co-ordinating dimension The distance between two co-ordinating planes.

Controlling dimension The key dimension—normally between co-ordinating planes—which is the crucial determining dimension in an assembly and which must remain sacrosanct while intermediate dimensions may be permitted some tolerance.

Work size The actual finished size of a component.

Permitted deviation (sometimes known as manufacturer's tolerance) The amount (plus or minus) by which the finished size of a component may vary from its stated work size and still be acceptable.

Dimension line The line drawn between two planes with a view to showing the dimension between them.

Extension line The line drawn from a plane which is to be dimensioned, and intersecting the dimension line.

Leader line The line joining a note with the object which is the subject of that note.

Dimensioning—some examples Appendix 5, dealing with non-active lines, gives examples of the types of dimension line recommended for different purposes. The following comments may be helpful in establishing the correct approach to dimensioning such diverse drawings as the site plan, primary element location plans, location and assembly sections and component and sub-component details.

To set out a building it is necessary to establish a datum parallel to one of the building's axes. The criteria by which this datum is selected will vary. Where there is an improvement line required for the site, or an established building line, these will obviously be important starting points. If the site is relatively uncluttered then existing physical features—boundary fencing, adjoining buildings, etc—will be used. In certain specialised structures orientation may be the overriding factor.

The important thing is that the chosen starting points should be unambiguous and clearly recognisable on site.

It is better to establish the datum some distance from the perimeter of the new building so that it may be pegged in as a permanent record during construction. The building may then be set out from it by offsets. A datum which coincides with one of the new building's faces will be obliterated as soon as excavation starts.

Where the construction is load-bearing the setting out dimension from the datum should be given to the outside face of the wall. Where the structure is framed, this dimension should be to grid centre-line.

The dimensioning of the location plan shown in 4.12 is largely self-explanatory. Note the three strips of dimensions along the external walls, the string picking up the grid being the outermost line of the three. Overall dimensions are included, partly as an arithmetical check for the dimensioner, partly to aid the estimator.

Generally speaking, internal setting out is effected by judiciously selected strings of dimensions. Where the "positioning of a given element is critical, however, (where, for example, it must be a precise distance from a certain wall face) it has been dimensioned from that face alone, to ensure that the setter out works in a similar fashion. When it is critical that a feature be in the centre of a wall face an 'equal/equal' indication has been given from its centre line.

Figures 4.13 and 4.14 show the role of the controlling dimension in vertical setting out. The salient levels dimensioned from the relevant datum (in this case the finished floor level) in the location section appear again as reference planes in the larger scale detail. The only comment that needs to be made about components and sub-components is the general one that they should be dimensioned to their finished sizes. This is particularly relevant when the material involved is timber.

A note to the effect that the finished section is to be 'ex 150 x 50' is too imprecise for a constructional world of off-site fabrication. Economy requires that the finished section should realistically be obtainable from one of the

standard sawn sections. To give a finished size of

150 x 50, for example, would result in the client paying for a large quantity of wood-shavings and sawdust.

4.13 The controlling dimension

Grids

The use of shadow grids has been around for a long time, particularly among the manufacturers of building systems, where components tend to be modular and junctions simple and standardised. They are applicable to traditional building as well however whenever a modular discipline exists, and when used with discretion can speed up the production of drawings and reduce the need for elaborate dimensioning.

Where grids are combined with the use of pre-printed sheets a half-tone is usually adopted for the printing of the grid itself, so that it appears on the finished print in a fainter line than those used for the rest of the drawing. In practical terms, the use of grids is limited to location plans, and they are of greatest benefit in projects where rationalisation of the design has restricted the size and position of the elements. In 4.15, for example, where the use of a grid of 6 mm squares has allowed each square to represent a 300 mm module at a scale of 1:50, the placing of the 100 mm partition has been limited to one of three conditions. It is either centred on a grid line, centred on a line midway between grid lines, or has one face coinciding with a grid line. Similarly the door-frame, with a co-ordinating dimension of 900 mm, is always situated so that it occupies three entire grids.

4.14 Vertical location of elements in the assembly section is given by reference to the planes established in 4.13
4.15 Modular discipline eliminates the need for complicated dimensioning by limiting the location of elements to certain standard situations (scale of original 1:50)

No dimensions are needed to locate such elements if the discipline for positioning them is established from the outset and is known to everyone using the drawings.

A word of warning however. It is not realistic to expect the man on site to set out a wall by counting grids and doing his own calculation. Dimensions should always be added to the grid for key setting-out positions, overall lengths, and controlling dimensions.

Title panels

The title panel should be at the bottom right-hand corner of the sheet, so that when the drawing is folded properly, the title and number are always clearly visible. Figure 4.16 shows the recommended method of folding various 'A'-sized sheets.

The format of the panel will vary, but it must make provision for the following (minimum) information to be displayed:

• name, address and telephone number of the issuing office

• name and address of the project

• title of the drawing

• title of the drawing

• scale of the drawing

• coded number of the drawing (assembly, location, etc, CI/SfB code and unique number in that series)

• reference, description and dates of subsequent revisions.

Optionally, the panel may carry further information, such as the name of the project architect, the names of the persons preparing and checking the drawing, office job reference, etc.

Figure 4.17 shows a suitable format, but many are available.

Title panels may either be pre-printed on to standard drawing sheets or supplied in the form of adhesive and transparent printed panels for sticking to the back of the completed negative.

Trimming lines and margins are unnecessary when standard 'A'-size sheets are used, since copy paper for dyeline printing almost invariably comes pre-cut to size. It is useful, however, if the line marking the left-hand edge of the title panel continues up for the full extent of the sheet, since this reserves a strip along the side of the sheet for the addition of notes, revisions, etc.

It is difficult to align ink plotters with pre-printed title panels, and for CAD use the panel is better inserted in the drawing file, (when the option of printing on continuous rolls remains a valid one.) For manual draughting the use of individual sheets is the only option.

When completing the title panel it is most important that the drawing title be stated simply and consistently, giving the casual searcher a brief but accurate and informative statement about the drawing's content. The following is a typical title which follows a logical pattern:

Location plan—level one—primary elements.

We are told, in sequence, that the drawing is in the location category; that it is a plan; the level at which the plan is taken; and, because this is an elementalised set of drawings, we are told finally the element which the drawing shows.

The identical title will appear in the drawing register. (See chapter 5.)

Sheet size

AO 841 x 1189

A1 594 x 841

Fold lines

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