FIRST TERM e – LEARNING NOTES
Subject :Technical Drawing
Topic : Freehand Drawing and Sketching (Woodwork and Metalwork)
Class :SSS 3 (BASIC 12)
Term : FIRST TERM e – LEARNING NOTES
Week :WEEK 6
TOPIC:ENGINEERING WORKING DRAWING
CONTENT (a) Examples of machines parts e.g. bracket, blocks, sleeve, cylinder etc.
(b) Machine assemblies e.g. parallel clamps, water taps, bench vice, bicycle pump etc.
Examples of machine parts
Draw the following views of the valve casing shown below.
(a) The given plan view
(b) A sectional front elevation on BB
(c) A sectional end view on AA
(d) An outside end view obtained by viewing the front elevation in the direction of C
SUB-TOPIC 2:ASSEMBLY DRAWING
Assembly drawing is a type of drawing in which all necessary fasteners are positioned for two or more components in a pictorials or orthographic drawing.
AIDS IN ASSEMBLY DRAWING
a. Identify the function of the assembly unit. This help you to select the type of component will fit on the main components or body.
b. Identify equality of dimensions. Knowing the complete function of a particular unit, recognize that for a part to fit into another. It must be such that the external dimension of the inner component must be less than or at the most equal to the internal dimension of other component.
THE MAJOR TYPES OF ASSEMBLY DRAWING
a. Detail assembly drawing.
b. General assembly.
c. Installation assembly drawing.
1. DETAILS ASSEMBLY DRAWING- This reveals the dimension and necessary information for the complete coupling and construction of the parts. The drawing is also useful in the woodwork industries.
2. GENERAL ASSEMBLY DRAWING- This identifies with the leaders attached to balloons inscribe of with numbers the main parts of the body and the movement of parts relative to one another. The main parts of the body with inscribe numbers are presented as shown below.
3. INSTALLATION ASSEMBLY DRAWING- It is commonly referred to as to a manual or guide and it is simplified that it aids those that cannot interpret technical drawing. It is used in the house, workshop and manufacturing industries.
Q1.The drawing shown above is the details of toy sewing machine. The body and the base are shown in first angle. The body fit into the base at D,the handle fit into the hole C in the crank and the crank fits into the body at A. The stem fit into body at B.
Draw in first angle projection, the following views of the assembly (a) front view on section P-P(b) Plan (c) end view in the direction of arrow E.
Read Technical drawing manual with solved past question by Ajayi E.K pages (212-224)
4. Technical drawing manual with solved past question by Ajayi E.K
5. Elements of Technical drawing for Senior Schools and Colleges by Osuji,U.S.APh.d and Akano,E.O. M.sc
TOPIC:SECTIONS AND SECTIONAL VIEW
I. Types of sections
II. Sectional views of building.
Sub-Topic:Types of Sections.
1. Full section. As shown in fig 2 below is called a full sectional view because the cutting plane passes complete through the object. The direction in which the plane is viewed is given by arrows at each end. The cutting plane is a long thin chain line with a thick long dash at each end. The arrows are placed with their points touching the centre of this thick dash.
The cutting place is selected by the draught man to show the interior of the object.
2. Half Section. Half section is used in symmetrical object that is with one half drawn in section and the other as an outside view. Thus two views and combined in one with a consequent saving of draughting time and space.
They have the disadvantage that the dimensioning of the internal feature is often difficult without using hidden detail lines. For this reason they are more often used for assembly drawn.
3. Revolving:- These section are drawn directly on an outside view and are used to show the local cross section of an arm, rib or similar feature. The cutting plane is assured to pass through the part at right angles to the axis and is then revolved into the plane of the paper. Revolved sections are often placed in the gap between the parts of an interrupted view.
4. Off-set section. As off-set required, it includes features which are not in a straight line. The position of the cutting plane must be shown in a view where it appears as a line and the resulting view should carry a title. Where the plane changes direction, thick dashes are used and these dashes touch to form a right angle. Note that at the places where the plane changes direction on the sectional view, no lines appear. There are two reasons for this, first the cutting of the details by the plane is imaginary, and secondly such lines would be crossed.
The drawing below gives details of a small locating block in first angle orthographic projection. Draw, full size, the following views of the assemble block in first angle projection
a. The front elevation
b. The plan. Note the sliding spindle should flush with the back of the fixed block when fully assembled.
i. Insert principal dimensions
ii. No hidden details may be required
c. Sectional end elevation in the direction of arrow Y-Y1
Q1. Sample Question with solution:
A cube, side 50 mm, is resting on H.P. on its base face with all the vertical faces equally inclined to V.P. It is cut by A.I.P. in such a way that the true shape of section is a regular hexagon. Find the inclination of C.P. with H.P and draw projections and the true shape of section. Also project auxiliary view on a plane parallel to cutting plane.
Q2: A square prism, side of base 50 mm and height 75 mm, is resting on H.P on its base with all vertical faces equally inclined to V.P. It is cut by A.I.P. inclined at 450 to the H.P passing through a point 55 mm above the base on the axis. Draw elevation, sectional plan and sectional auxiliary plan along with the section on a plane parallel to cutting plane.
Q3. A frustum of hexagonal pyramid, side of base 35 mm and height 50 mm, is a cutting from a pyramid of height 85 mm, is standing upright with base on H.P and axis parallel to V.P. It is cut by A.V.P making 550 with V.P and remaining 20 mm away from the axis. Draw plan, sectional elevation, sectional side view and the true shape of section.