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Lecture notes for a 2-credit hour course, FT 101, titled 'Basic Engineering Drawing and Communication' offered in the Department of Food Science and Technology at Sokoine University of Agriculture. The notes cover topics on communication, technical report writing, pictorial communication, and engineering drawing. The assessment for the course consists of weekly practical reports, practical tests, theory tests, and an end-of-semester examination.
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FT 101: 2 Credit Hours: ( 30 Lect. hrs : 0 Sem. hrs : 60 Pract. hrs )
Prerequisite: None Instructors: Dr. J J Mpagalile Dr. W R W Ballegu ( Mobile: 0754 463 016 ; E-Mail: [email protected]) Department of Food Science and Technology, SUA.
Objective: To equip students with basic skills required in engineering drawings, electrical circuit diagrams, and communication. Course Purpose and forms of communication; technical communication, report writing, drawing, Contents: reprographics, engineering drawing, sketching, pictorial projections, paper sizes, scales, conventions in layout, lettering and representation of components, tolerances, assembly drawings, K-parts list, exercises in machine drawings, structural drawings and design. Selection of machine components such as; V-belts, flat-belts and pulleys. Simple stress calculations for shafts and structural members.
Course The Course Assessment (culminating to the Final Grade), will be made up of the Assessment: following four components; (i) Weekly Practical Reports --- 20% (ii) Practical Tests --- 20% (iii) Theory Tests --- 20% (iv) End of Semester Examination --- 40%
Delmar Publishers. Albany, New York, pp. 370
McGraw-Hill, Kogakusho Ltd, Tokyo
Technical Drawing – 8th^ Edition
Part – 1: COMMUNICATION
Definition: Communication is defined as, “the act of communicating, that is, passing on news, information, feelings etc.” (Oxford Students’ Dictionary of Current English – 1985)
The purpose of communication – irrespective of the form/means in which it is conveyed – is to pass a message from one entity (a person or group of people) to another entity (person or group) in the most convenient way and with minimum distortion or ambiguity.
The two main forms of communication are through audio and visual means. Audio means rely on sound signals that are perceived by ears. Sound producing/receiving devices are used for this purpose. Visual means on the other hand, depend on light signals (images) that are perceived by eyes. Image producing/receiving devices are used for this purpose. This may include things like text, drawings, figures, photographs, video images, TV images, images of real objects etc. Other human senses are sometimes used for communication (e.g. a touch to attract attention, braille text for the blind, etc).
Technical communication is an advanced form of communication whereby people of the same trade (profession) can convey messages to one another more accurately and precisely. To achieve this, a technical language, which is well standardized, is needed (e.g. botanical names for plant scientists, etc).
Definition: “ Standardization is the process of formulating and applying rules for an orderly approach to a specific activity for the benefit and with the cooperation of all concerned, and in particular for the promotion of optimum overall economy taking due account of functional conditions and safety requirements.” (ISO – International Organization for Standardization) Standards are set at different levels. There are local standards, national standards, regional standards and international standards. Typical examples of the different levels of standards may include;
It is always desirable to adhere to international standards, particularly the ISO standards that employ SI units. Standardization serves five main objectives;
All sources of information cited in the literature review and elsewhere. Avoid including general reading materials that were used to obtain a general background on the subject matter. o Appendices Any relevant information, which you strongly feel is necessary for the wholesomeness of the report, but which could not be conveniently fitted into the bulk of the report.
Pictorial communication includes drawings and photographs. Drawings and photographs, where appropriate, convey the message more accurately than a passage of words. Photographs are more accurate and sometimes the true colors of the object are displayed. However, photographs are expensive, less informative and their magnification is limited in terms of clarity. On the other hand, drawings are cheap, clearer and easy to understand. They are therefore, in most cases, more preferred than photographs.
Why Engineering Drawing? As a Food Scientist and Technologist, you will inevitably be required to communicate with different people for different reasons. In some situations, communications will be sufficiently taken care of by use of plain text. However in other situations, text alone may not suffice and a more specialized form of communication (technical/engineering drawing) may prove irreplaceably useful.
Drawing (just like photography) is one of the basic forms of visual communication. Drawing is used to record objects and actions of everyday life in an easily recognizable manner. There are two major types of drawings: artistic drawings and technical drawings.
Management Clients Controllers^ Quality
Government Agencies
Engineers (^) ManufacturersMachine Manufacturers^ Spare parts
Artistic Drawings These are a form of freehand representation that makes use of pictures to provide a general impression of the object being drawn. There are no hard rules or standards in the preparation of artistic drawings. They are simply drawn by artists, based more or less on one’s talent and skills. Although these drawings are often very attractive, they find very limited use in the world of science. Technical Drawings These are detailed drawings drawn accurately and precisely. They are pictures that have been prepared with the aid of mathematical instruments in order to record and transmit technical information. They provide an exact and complete description of things that are to be built or manufactured. o Technical drawings do not portray the objects the way they directly appear to the eye o They make use of many specialized symbols and conventions in order to transmit technical information clearly and exactly. o To understand and correctly interpret technical drawings, one needs to acquaint oneself with the fundamentals of technical drawing – hence the purpose of this course.
These are drawings in which the object is drawn in three dimensions (3-D), i.e. three sides of the object appear in one drawing. Normally only one drawing is prepared/used. o They are used extensively in artistic drawing. o A three dimensional view (i.e. shows length, width and height of the object simultaneously) o Provides only a general impression of the shape of the object by allowing the observer to see three of its sides as well as its three overall dimensions o An exact and complete description of its shape, particularly as applied to its slots on the underside is lacking. Two standards are currently used for axonometric projections: diametric projection and isometric projection.
Dimetric Projection In diametric projection, all dimensions along two axes are drawn to TRUE SIZE. The dimensions along the third axis are HALVED. This projection is preferred when one view of the object is to be emphasized than the other two views (i.e. when that one view is of more interest than the other views). Example: A cube of length L
True Size
Half Size
7 o^42 o
Half L
The Front View (ABCD) – abbreviated as FV, is that view of utmost importance in representing the object (normally the most complicated of all the views) as seen when the object is placed directly in front of the viewer. This view generally serves to represent the object (e.g. a work piece) in the most common position in which it is used. It is normally the first view to be drawn – other views following thereafter. The Rear View – RV (EFGH) is directly opposite the FV at the back of the object. The Right Hand Side View – RHSV (BFGC) and the Left Hand Side View – LHSV (AEHD) appear on the right and left sides of the object, respectively. The Top (ABFE) and Bottom (DCGH) Views are at the top and bottom sides of the FV. As you must have noted, these six views are at right angles to one another. Standard Orthographic Projections Two standards are commonly in use in orthographic projection of drawings; the First Angle Projection (European projection) and the Third Angle Projection (American projection). It should be noted that corresponding views are identical in both methods of projection except for their relative positions on the drawing paper. The First Angle Projection
Symbol:
In here, the front view (A) is the basis (reference) and the other views are drawn as ‘shadows’ of that view. That is, the left hand side view for instance is drawn on the right side of the front view. Similarly the top view (plan) is drawn at the bottom of the front view, etc. The Third Angle Projection
Symbol:
Left Hand Side View(AEHD) Front View (ABCD) Bottom View(DHGC)
Top View (PLAN)(ABFE) Rear View (EFGH) Right Hand Side
In here, the front view is the basis (just as before) but the other views are drawn as ‘ reflections’ of that view. The left hand side view is drawn on the left hand side of the front view. Similarly, the top view (plan) is drawn at the top of the front view.
Example: The Front View (FV), Left Hand Side View (LHSV) and Top View (PLAN) of the given object
First Angle Projection
(ii) Format A4 is exclusively used in an upright position. The other formats (which are lager in size than A4) may be used in an upright position or horizontal position. Folding Only format A4 is convenient for filling. Other formats (larger in size) exceed the size of the file and thus must be folded before filing. Drawings which that do not need fastening are fold in a logical way to give an A4 size. However, for those drawings that must be fastened, they must be fold in a standardized way as follows. Format A1 --- (594 X 841 mm)
Format A2 --- (420 X 594 mm)
The objects we encounter in our day-to-day life are usually either too large or too small to be drawn to their true size. For instance a car or a building can be drawn to its true size if, and only if, we use a piece of paper that is large enough to accommodate the true dimensions of that car or building. But as we have noted above, the largest size of paper (under ISO standard) is A0 (841-mm X 1189-mm), which is a lot smaller than these objects. The discrepancy between the actual sizes of objects and the size of the papers we use for drawing necessitates us to prepare drawings that are either smaller or bigger in size than the actual objects. This is only possible through the use of scales. o A scale is simply the ratio of the linear dimension appearing on the drawing compared to the corresponding linear dimension on the object o A scale has no units as it is simply a ratio (i.e. dimension on drawing : dimension on object ) o Scales are used either for enlargements or reductions
The recommended scales in Engineering Drawing are
True Size 1: Scales for Reduction
Scales for Enlargement
The scale of 1:1 (read as one-to-one) implies the object has been drawn to true size. A scale of say 2: (read as two-to-one) implies that the object has been enlarged twice its true size. A scale of 1:2 (read as one-to-two) implies that the object has been reduced to its half size, etc.
Lines
In Engineering Drawing, we make use of different lines and line styles to convey the desired message. These lines differ in (i) thickness and (ii) style. Typical uses of these lines are summarized below.
Type of Line and Designation Applications
Recommended line thickness [mm] PAPER SIZE A4/A3/A2 A1/A
A:
A continuous thick line
B: A continuous thin line
A continuous wavy line
A short thin dashes
Lettering Lettering used in engineering drawing is referred to as a Single Stroke, Commercial Gothic. The main advantage of this font is that it is easy to read. This makes the information on engineering drawing easy to understand. The letters can be made either freehand or by use of lettering devices. The general construction of vertical gothic letters and numerals is shown below (next page). Hints on Lettering
Font: Square721 BT Font Size: 15
Title Block In every engineering drawing, a Title Block is included at the bottom right-hand corner. The Title Blocks are locally standardized but should be designed in such a way that it can be easily understood. The information needed in any standard Title Block is normally: o Name of the Firm/School/College o Name of the Object (Work piece) o Number of the drawing (particularly useful for reference where more than one drawing are concerned --- typically in assembly drawings) o Format of the paper used (paper size) o Scale used o Dimensioning unit (usually millimeters --- mm)
A a
B b
C c
D d
E e
F f
G g
H h
I i
J j
K k
L l
M m N n
O o
P p
Q q
R r
S s
T t
U u
V v
W w
X x
Y y
Z z 0 1 2 3 4 5 6 7 8 9
o Symbol for the method of projection used o Date when the drawing was finished o Name of the draftsman (draughtsman) --- e.g. student name if it is a normal class exercise o Name of the person who checked the drawing o Remarks
The Title Block used at the then Faculty of Engineering (University of Dar es Salaam) is shown below. For the purpose of this course, we will adopt the same. 30 40 PROJECTION: SCALE: DRAWN: DIMENSION: GROUP: Food Scie. & Techn. DATE: CHECKED:
Parts List The Parts List is an essential component in any assembly drawing. It is usually drawn on top of the Title Block. The Parts Lists usually have the same width as the Title Block, i.e. 180-mm. The height depends on the number of items to be included. The following information is usually included in the Parts List; o A --- Part reference number o B --- Name of the part o C --- Number of parts required in an assembly o D --- Material used to manufacture the part o E --- Indication of standard or dimension o F --- Drawing number
Usually engineering drawings (of real life objects) are prepared in three stages; sketches, handdrafts and detail drawings. This sequence is not very binding but most workers find it very useful to work in that order.
Sketching is almost always the first step in the preparation of Engineering Drawings (ED). The work piece (object) is carefully studied and all the necessary dimensions are measured. The views that are necessary to completely describe the object are very roughly drawn (free hand). All dimensions are
♦ The size of a T-Square is determined by its blade length. Blade lengths of 60-mm, 90-mm, 120- mm and 150-mm are common. ♦ USES: + The T-Square is used primarily as a guide for drawing horizontal parallel lines.
ii) Parallel Rule ♦ This is a straight edge that is permanently mounted on a drawing board or drafting table by means of pulleys and guide ropes. ♦ It enables us to draw horizontal lines quite fast. iii) Set Square ♦ Set Squares (SSs) are transparent, triangular-shaped drawing instruments that are used with either a T-Square or parallel rule for drawing vertical or inclined lines.
♦ The height/length of SSs is typically 15-cm, 20-cm, and 25-cm.
90 o^ / 60o^ / 30o^90 o^ / 45o^ / 45o
iv) Drafting Machine ♦ This is a machine/device with two scales set at right angles to one another. ♦ It can be moved easily and quickly to any location on the drawing surface. ♦ The edges of the scale are used for measuring as well as for drawing.
v) Rule Scale ♦ This is a measuring instrument and should not be used to draw line ♦ They are available in flat and triangular styles. The triangular style is more common in schools ♦ They can be used to prepare drawings to: full scale (true size, reduced scale and enlarged scale
vi) Wooden Pencil
A set of rules Drawing table
♦ Pencils in general (including wooden pencils) are graded depending on the degree of hardness. They include;
viii) Erasing Shield ♦ This is a very thin plastic (or metal) instrument that has a number of holes of various shapes and sizes on it ♦ The shield permits erasure to be made within confined areas of a drawing, other information remaining in place
Spacing of Views Spacing of views on the drawing paper is extremely important. The general appearance of the drawing is significantly affected if the different views are poorly spaced. Spacing of views requires us to place the views on the drawing paper such that the spaces between the views and between the views and the limits of the drawing space are roughly equal (horizontally and vertically).
Steps
Drawing Paper (Format A-???) Drawing Space Views (FV, LHSD, TV) Wear and tear margins (5-mm) Filing margin (25-mm)
