Engineering Drawing for Manufacture phần 5 pps

62 Engineering drawing for manufacture

The list of items appropriate to the assembly drawing of the vice

is shown in Figure 3.1. In this case three columns are shown, the

item reference (part number) the number of each component

required in the assembly (number of) and the description of the

item. In this case there are three columns of information. Other

columns can be added as appropriate. Examples of other columns

are: material, stock number, delivery date, remarks and relevant

ISO standards.

The vertical sequence of the item entries should be in numerical

order. When the item list is included on the assembly drawing as in

Figure 3.1, the items should read from bottom to top in numerical

order with the column headings at the very bottom. However, if the

item list is on a separate drawing, on its own, the sequence is to be

from top to bottom with the headings at the top. The standard that

gives details of item lists is ISO 7573:1983.

3.10 Colours

Colours are not normally used in engineering drawing. Indeed, in

ISO 128:1982, the use of colour is 'not recommended'. The reason

for this is for the convenience of document transmission that can be

more easily achieved if the colour is always black. Hence, the stan￾d~irds recommend the use of the different line thicknesses and line

designations such that discrimination is obtained without the use of

colour.

3.11 Draughtman's licence

The term draughtsman's licence refers to the freedom a draughtsman

has in expressing the design in drawing form. This applies, irre￾spective of whether a drawing is drawn by hand or on a CAD system.

Any component can be represented in a variety of ways in terms of

the drawing convention (i.e., number of views, sections, viewing

direction, etc.) and the method of imparting the manufacturing

details (i.e., the dimensions, tolerances and datum surfaces). The

problem is that there are as many ways of drawing a part as there are

draughtsmen or indeed draughtswomen. For example, in Figure

3.3, for the detailed drawing of the hardened insert I chose to only

draw the left-hand part of the front elevation. I could just as well