This chapter is related with the formal ways of presenting a
part to be manufactured in detail and the structures that is formed by
several parts aligned to each others by appropriate assembly elements such
as threaded fasteners, keys, springs, etc.
WORKING DRAWINGS NEEDED FOR PRODUCTION
The drawings that are used to give information for the
manufacture or construction of a machine are called as working
drawings. Working drawings must include all the knowledge for the
production of a machine or structure explicitly so that no further
information is required to complete the production. The description given
by the set of working drawings will include:
- The graphical representation of the shape of each part, namely shape
- The dimensions of each part; size description.
- Explanatory notes on the individual drawings, giving the
specifications of material, heat treatment, and surface finish.
- A descriptive title on each drawing.
- Relationships of each part to the others (in assembly drawings)
- Part list.
In general, set of drawings include two classes of drawings; detail
drawings, supplying the information in topics 1 to 4, and an assembly
drawing, supplying the information about the location and relationship of
the parts, topic 5.
It must be noted that the working drawings used for purposes of
manufacturing are superior to design layouts. Design layouts are prototype
assembly drawings from which working drawings evolve. The below figure is
an example of a design layout.
A portion of design layout.
If mass production of the parts is concerned, "operation" or
"job" sheets describing the seperate manufacturing steps should be
prepared. These sheets also indicates the use and kinds of any special
SPECIFIC TYPES OF WORKING DRAWINGS
We will now turn our attention to particular types of
drawings that are used in the production of parts. Design layout
drawings are part of the initial design procedure.
- Detail Drawings : A detail
drawing is the drawing of a single part that includes a complete and
exact description its form, dimensions, and construction. The worker
must clearly understand the shape, size, material, and surface finish of
a part, what shop operations are necessary; what limits of accuracy must
be observed from the detail drawing. Following figure is an example of a
A commercial detail
drawings are formed by carefully studying the initial design layouts.
Use is made of the scale of the design layout, dimensions that may be
given, and all notes provided. Approved standarts for the specific
company involved with respect to lettering style, dimensioning
techniques, position of notes must be included in detail drawings.
- In general
working drawings are checked by an experinced person responsible for any
possible error, when it is finished. This step is the final
"proofreading" and cannot be carried out by the person who has made the
drawing. The necessary information should be preserved for the future
use and reference.
- 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 sofisticated 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
- 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 .
- 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 illlustrate; headstock, tailstock, and gearbox unit
assemblies should be included in the drawing of a lathe.
A unit assembly drawing.
- 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.
- The bill of material is a tabulated list placed either on the
assembly drawing or on a seperate sheet. The list gives the part
numbers, names, quantities, material and
sometimes stock sizes of raw material, detail drawing number, etc. The
term "bill of material" is usually used in structural and architectural
drawing whereas the term "part list" is used in machine-drawing
- Tabular Drawings : A tabular drawing,
either assembly or detail, is one on which the dimension values are
replaced by reference letters, and an accompanying table lists the
corresponding dimensions for a series of sizes of the machine or part,
thus one drawing serves for a range covered. If parts are produced in a
variety of sizes, using tabular system will be logical, but there is a
serious risk of misreading the table.
An outline assembly drawing (tabular).
- Standardized Drawings : The difficulties of
the tabular drawings are overcomed by making "standardized drawings".
These drawings are complete except the actual figured dimensions. By
offset printing or black and white reproduction on vellum paper these
standard drawings are reproduced and dimensioned seperately for the
various sizes. Following figure is an example of standardized drawing.
A standard drawing and a filled-in
- Set of Drawings : A
complete set of working drawings consist of detail sheets and assembly
sheets, the former gives all the necessary information for the
manufacture of each of the individual parts and the latter showing the
parts as assembled as a finished structure or machine. The set includes
also the parts list and also may include further information such as
An example of assembling
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