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READING AND INTERPRETING DRAWINGS
As you work through the Practical Woodworking course, you will be issued with various working drawings and you will be expected to interpret these drawings and be able to pick out relevant information needed to manufacture a model. Working drawings are used extensively by various professionals from joiners, plumbers and electricians to engineers and architects.
BASIC DRAWING CONVENTIONS
In order that everyone who needs to use a working drawing is able to interpret the drawing and pick out the relevant information needed, all working drawings are done according to a set of rules set out by the British Standards Institute (BSI). The set of rules are known as drawing conventions. The purpose of this section is to introduce you to the BSI drawing conventions used in working drawings, and to enable you to understand what the various conventions that have been used in the working drawings represent, and what information you would expect to find in a working drawing.
LINE TYPES
Firstly, you will find that there are a variety of line types in use and they all mean something different. the four main line types that you will find in a working drawing are outlines, centre lines, hidden detail lines and dimension lines. Each of the line types and what they represent are shown.
OUTLINE
HIDDEN DETAIL LINE
CENTRE LINE
DIMENSION LINE
The dimension line is shown as a thin continuous line with solid arrow heads at either end. The points of the arrows should be touching the extension line. There should be a small gap between the object being dimensioned and the extension line. The actual size of the part of the object being dimensioned should sit centrally, just above the dimension line.
Dimensions on a working drawing signify the actual size of a part of an objct. All sizes shown will be in millimetres unless it is stated otherwise. Millimetres are used as that is the degree of accuracy required in woodwork. A working drawing will inclide measurements to indicate the sizes of individual parts and the overall length, breadth and thickness of the assembld objects. The 4 main dimension types that you will find in a working drawing are linar, radial, angular and diametric dimensions. Each of the methods of dimensioning and what they represent are shown below
A linear dimension is used to show the size of an object in one dimension only, the length or width of the object.
When an object has a curve, an arc or a founded corner to be created, you will be given a radial dimension. If a radial dimension is required, an R before the number denotes the radius.
An angular dimension, like the example shown, is used to show the angle a part is to be either cut or shaped to. The most common place you will find an angular dimension is on a mitre joint where you are required to cut a joint to 45° or a chamfer.
Diametric dimensions, like the examples shown are used to show the size of a hole that is to be either cut or drilled out. A dimension showing a diameter of a circle will always have the symbol Ø before the number.
Another feature of a working drawing is the way it is laid out. This is another drawing convention used to ensure that all working drawings are laid out in a standardised way. The 3rd Angle Projection symbol (shown to the bottom right) is used to indicate the order in which the different views of the object are laid out. For example, the front view, called the elevation, is placed under the plan view, which is the view of the model looking at it from above.
For more information, see the Reading & Interpreting working drawings notes in the theory tab.
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