Assembly Drawing

Assembly Drawings : A complete assembly drawing is presentation of the product or structure put together, showing all parts in their operational positions. The seperate parts come to the assembly department after their manufacturing processes are finssihed and in this department they are put together according the assembly drawings. Small machining operations may be necessary during assembly process such as drilling, reaming, or hand finishing. For such cases, assembly drawings include a note explaining the required operation and give the dimensions for the alignment or location of the pieces.

Several different methods can be used to produce assembly drawings; the simplest one tracing from the design layouts. This method is inferior to the method that the assembly drawing is produced from the dimensions of detail drawings if the accuracy of checking considered. Of course the second method is very time consuming. Whereas, the Computer Aided Drafting can be a huge timesaver when an assembly drawing is being produced. Nowadays, there are so sophisticated CAD programs and equipments; almost all the manufacturers use these programs to recover high initial costs. Although many assembly drawings do not need dimensions, the overall dimensions and distances between the centers or from part to part of the different pieces to clarify the relationship of the parts with each others. An assembly drawing should not be overloaded with detail.

Assembly drawings should include referance letters and numbers representing the different parts. These part numbers usually enclosed by circles with a leader pointing to the piece .

Parts Identification

The method of identifying the parts must be clear and unambiguous. The equipment as represented on the general arrangement drawing and the sub-assemblies as shown on the arrangement and assembly drawing should be clearly identified with plant item numbers. The relevant drawing numbers are obtained by reference to the plant items list.   Plant items are annotated by leader lines to a double balloon.

The detail drawings are sub items of the arrangement drawings and are identified on the arrangement and assembly drawings.   Typically an item say a conveyor frame may be identified from the conveyor plant item number e.g. H1040/3 . Optionally it may be identified using the arrangement drawing number e.g. A0 12500 /3.   The frame will also have a discrete detail drawing number e.g A2 12503

The fabricated items which are based on sub-parts welded together should be identified as details but the individual sub-parts should be identified in a different way to avoid ambiguity.    One option is to number the fabricated sub-parts alphabetically e.g a, b, c ...or as a combination of the fabrication detail number and the part number i.e 3/a , 3/b.... These sub-parts do not need to be identified as separate parts because following fabrication they will not exist as separate parts.   If the sub-parts are complicated shapes or machined items and they cannot be described in sufficient detail on the fabrication drawing they

should be drawn as separate detail drawings but still identified as sub-parts of the fabrication detail.

Parts list

Each part is given a unique number, indicated on the drawing by a circle with the number in it and a leader line pointing to the part. The leader line terminates in an arrow if the line touches the edge of the component, or in a circle if the line terminates inside the part.

A table of parts should be added to the drawing to identify each part, an example of a parts list is shown below:

Item No. Description Qty Material Remarks The first three items; Item No., Description, and Quantity should be completed for every distint part on your drawing. (i.e. the number of duplicate parts are recorded in the quantity). The material is used for components that are being made within the company. The Remarks column is useful for specifying a manufacturers part number when using bough-in parts.

Parts of Assembly

A unit assembly (subassembly) is a drawing of a related group of parts and used to show the assembly of complicated machinery for which it would be practically impossible to show all the features on one drawing. To illustrate; headstock, tailstock, and gearbox unit assemblies should be included in the drawing of a lathe.

An outline assembly is used to describe the exterior shape of a machine or structure, so it contains only the primary dimensions. If it is made for catalogs or illustrative purposes, dimensions are often omitted. They are also called as installation drawings.

An assembly working drawing includes all the necessary information for producing a machine or structure on one drawing. This requires providing adequate orthographic views together with dimensions.

A diagram drawing is an assembly showing ,symbolically, installation of equipment and often made in pictorial form.