Detail and Assembly Drawing Chapter Nine Working Drawings: Detail and Assembly Drawing

Purpose This chapter provides an overview of how to: make a detail drawing following standard procedures make an assembly drawing following standard procedures prepare a set of working drawings.

Detail drawings Detail drawings should contain enough information to manufacture the part as well as suitable, fully dimensioned orthogonal views of each part, with other information that may be required in the manufacturing process. Detail drawings should at least contain the information on the following slides.

Detail drawings Sufficient orthogonal views of the part concerned Dimensions and instructional notes Scale used Projection used, for example third angle Drafting standard reference, for example AS1100 Part 101 Name or title of drawing Drawing numbers Dimensional units which apply Tolerances where necessary Surface texture requirements

Detail drawings Special treatments needed (heat, metallic coatings, paint, etc.) Reference to a particular assembly if applicable Type of material used Names of drafter, checker, approver, etc. Relevant dates of action by those concerned Zone reference system when necessary Revisions or modifications Drawing sheet size Name of company or department as applicable Drawing sheet reference, for example sheet 1 of 2

Detail drawings It is preferable to draw only one item on a single drawing sheet; however, where individual parts are simple and it is more convenient to group them on one sheet you can create multi-detail drawings. It is common practice for firms to print their own drawing sheets with a drawing frame and title block in order to standardise the general information provided and to ensure that such information is included on all drawings. Figure 9.1, p.245, illustrates the layout of three separate detail drawings of parts of a machine screw jack.

Detail drawings Note that each of these drawings is referenced to the assembly drawing of the jack, shown in Figure 9.2 (p.245). Each drawing in Figure 9.1 was originally issued on 9.4.00, but a revision was carried out to the thread on the ‘spindle’ and ‘jack body’ by changing it from a Whitworth to a metric thread form. These revisions have been inserted on the drawing, and a record of them tabulated in the top right-hand corner on 1.6.01.

Detail drawings When such a revision does not affect the interchangeability of a part, the revision may be carried out on the old drawing. Where interchangeability is affected, a new drawing number should be raised.

Assembly drawings Assembly drawings show how components are fitted together to make a complete component. Subassembly is a product unit which combines with other subassemblies to make an assembly. For example, an assembly drawing of a motorcar engine would show a number of complete units included on the drawing, such as the distributor, generator, carburettor, etc. Each of these units is referred to as a subassembly of the engine assembly.

Assembly drawings There are basically two types of assembly drawings: general assembly – where the main purpose is to identify the individual components and show their working relationship, e.g. Figure 9.2, p.246. working or detailed assembly – a combined detail and general assembly drawing which fulfils the function of both types.

Features of general assembly drawing Views are selected which show how the parts fit together and indicate how the unit may function. Sectional views are used extensively in this type of drawing to facilitate 1 and to eliminate the use of hidden detail lines where possible. Dimensions which relate to the function of the unit as a whole are indicated; for example, Figure 9.2 indicates the maximum and minimum operating heights of the jack.

Features of general assembly drawing Individual components are identified by the use of numbers contained in circles which are connected by leaders to the related parts. A parts list relates to the numbers on the drawing and identifies the component. A revisions table is provided to record modifications to individual components which may occur from time to time. Some assemblies may be so large that it is necessary to draw different views of the assembly on separate sheets.

Features of a working assembly drawing Only simple assemblies are drawn in this manner, as views have to be chosen which show the assembly relationship as well as sufficient dimensional details of individual components to enable their manufacture. It is ideally suited to furniture construction drawings where the assembly views are not complex and details of joints may be enlarged and shown as partial views.

Assembly drawings Examples of working assembly drawings are the fan, and pulley and shaft assemblies shown on page 257. These are not complete drawings as tolerances, title blocks, material lists, etc., are omitted. General assembly drawings do not require information on the manufacture of individual parts, e.g. surface finish, tolerances or treatments. However, assembly instructions (see note zone B2, Figure 9.2) are required, as are dimensions which may be used for installation purposes or which are relevant to the operation of the assembly as a working unit (see note zone B4, Figure 9.2).

Working drawings A set of working drawings includes detail drawings of the individual parts together with an assembly drawing of the assembled unit. For example, a set of working drawings for the machine screw jack would include the three detail drawings shown in Figure 9.1 plus the assembly drawing, Figure 9.2.

Summary To enable a product to be manufactured a set of working drawings are required. These consist of detail drawings ( that include features such as tolerances and surface finish) and assembly drawings (that show how components fit together).