Engineering Drawing

True lengths and auxiliary views

An isometric view of a rectangular block is shown in Fig. 11.1. The corners of the block are used to position a line DF in space. Three orthographic views in firstangle projection are given in Fig. 11.2, and it will be apparent that the projected length of the line DF in each of the views will be equal in length to the diagonals across each of the rectangular faces. A cross check with the isometric view will clearly show that the true length of line DF must be greater than any of the diagonals...

Third angle projection

The difference between first and third angle projection is in the arrangement of views and, with reference to the illustration in Fig. 4.4, views are now positioned as follows View B from the left is placed on the left, View C from the right is placed on the right, View D from above is placed above, View E from below is placed underneath. Study the rearrangement shown below in Fig. 4.4 and remember the above rules because it is vital that the principles of first and third angle projection are...

Sections and sectional views

A section is used to show the detail of a component, or an assembly, on a particular plane which is known as the cutting plane. A simple bracket is shown in Fig. 8.1 and it is required to draw three sectional views. Assume that you had a bracket and cut it with a hacksaw along the line marked B-B. If you looked in the direction of the arrows then the end view B-B in the solution Fig. 8.2 , would face the viewer and the surface indicated by the cross hatching would be the actual metal which the...

Threads are so regularly used on engineering drawings that recognizable conventions are required to save draughting time. Figure 15.12 shows the convention for a male thread. The thread runout along the shank of the stud is indicated by a line drawn at 30 to the thread axis. The minor diameter of the thread is shown by parallel lines and in the end elevation the projected circle is not continuous. The break in the inside circle distinguishes the end elevation of a male thread from a female...

Dimensioning counterbores

A drilling machine is used for this operation, and a typical counterboring tool is shown in Fig. 14.26. The operation involves enlarging existing holes, and the depth of the enlarged hole is controlled by a stop on the drilling machine. The location of the counterbored hole is assisted by a pilot at the tip of the tool which is a clearance fit in the previously drilled hole. A typical use for a counterbored hole is to provide a recess for the head of a screw, as shown in Fig. 14.27 or a flat...

Development of patterns from sheet materials

Many articles such as cans, pipes, elbows, boxes, ducting, hoppers, etc. are manufactured from thin sheet materials. Generally a template is produced from an orthographic drawing when small quantities are required larger quantities may justify the use of press tools , and the template will include allowances for bending and seams, bearing in mind the thickness of material used. Exposed edges which may be dangerous can be wired or folded, and these processes also give added strength, e.g....

Methods of drawing an ellipse

Construct two concentric circles equal in diameter to the major and minor axes of the required ellipse. Let these diameters be AB and CD in Fig. 10.1. Fig. 10.1 Two-circle construction for an ellipse Fig. 10.1 Two-circle construction for an ellipse Divide the circles into any number of parts the parts do not necessarily have to be equal. The radial lines now cross the inner and outer circles. Where the radial lines cross the outer circle, draw short lines parallel to the minor axis CD. Where...

Dimensioning irregular curves

Irregular curves may be dimensioned by the use of ordinates. To illustrate the use of ordinates, a section through the hull of a boat is shown Fig. 14.14 . Since the hull is symmetrical about the vertical centre line it is not necessary to draw both halves in full and if the curve is presented in this manner then two short thick parallel lines are drawn at each end of the profile at right angles to the centre line. The outline is also extended slightly beyond the centre line to indicate that...

Worked examples in machine drawing

Examination questions generally relate to single parts or assemblies of detailed components, and test the students' ability to draw sectional and outside views. British Standards refer to 'views' but other terms have been traditionally used in technical drawing. The front or side view of a house is quite likely to be known as an elevation and a 'birds eye view' as a plan. These expressions are freely used. The examples which follow are of examination standard and a student draughtsman would be...

First angle projection examples with plotted curves

In orthographic projection, all widths in the end view are equal in size to depths in the plan view, and of course the opposite is true that some dimensions required to complete end views may be obtained from given plan views. Figure 4.21 shows part of a solid circular bar which has been cut at an angle of 30 with the horizontal axis. Point A is at any position along the sloping face. If a horizontal line is drawn through A across to the end view then the width of the chord is dimension X. This...

Unilateral and bilateral limits

Figure 19.10 shows an example of unilateral limits, where the maximum and minimum limits of size are disposed on the same side of the basic size. This system is preferred since the basic size is used for the GO limit gauge changes in the magnitude of the tolerance affect only the size of the other gauge dimension, the NOT GO gauge size. Figure 19.11 shows an example of bilateral limits, where the limits are disposed above and below the basic size. Minimum limit Maximum limit Fig. 19.10...

Drawing office management and organization

Every article used in our day-to-day lives will probably have been produced as a result of solutions to a sequence of operations and considerations, namely The initial stage will commence when an original marketable idea is seen to have a possible course of development. The concept will probably be viewed from an artistic and a technological perspective. The appearance and visual aspects of a product are very important in creating an acceptable good first impression. The technologist faces the...

The following examples are meant to convey to the reader the extensive range of draughting facilities available from software associated with basic programs. Obviously there is a certain amount of overlap in the scope of programs and often alternative ways of performing similar operations. Figures 3.6 and 3.7 show pictorial drawings of an engine development. A pictorial view can easily be generated after drawing orthographic views, which give the dimensions in three planes at right angles to...

Dimensioning keyways parallel keys

The method of dimensioning a parallel shaft is shown in Fig. 17.15, and a parallel hub in Fig. 17.16. Note that in each case it is essential to show the dimension to the bottom of the keyway measured across the diameter of the shaft and the bore of the hub. This practice cannot be used where either the shaft or hub is tapered, and Fig. 17.17 shows the method of dimensioning a keyway for a square or rectangular parallel key in a tapered shaft, where the keyway depth is shown from the outside...

Combined detail and assembly drawings

It is sometimes convenient to illustrate details with their assembly drawing on the same sheet. This practice is particularly suited to small 'one-off' or limited-production-run assemblies. It not only reduces the actual number of drawings, but also the drawing-office time spent in scheduling and printing. Figure 7.5 shows a simple application of an assembly of this type. 7.3 Assembly drawing of gear and bearing Fig. 7.5 Combined detail and assembly drawing of hub-puller

Geometrical constructions and tangency

Students will often experience difficulty in handling problems involving two and three dimensional geometrical constructions. The examples in Chapters 9 to 13 are included in order to provide a background in solving engineering problems connected with lines, planes and space. The separate chapters are grouped around applications having similar principles. Copying a selection of these examples on the drawing board or on CAD equipment will certainly enable the reader to gain confidence. It will...

Bushed bearing bracket

Front and end views of a bushed bearing bracket are shown in Fig. 18.1. Copy the given front view and project from it a sectional end view and a sectional plan view taken from cutting planes A-A and B-B. Figure 18.2 shows details of a table for a drilling machine. Draw half full size the following views a A front view taken as a section along the cutting plane A-A. b The given plan view with hidden detail. c An end view projected to the left of the front view with hidden detail included. 5...

Locking and retaining devices

The function of a locking device is to prevent loosening or disengagement of mating components which may be operating under varying conditions of stress, temperature and vibration. The effectiveness of the locking device may be vital to safety. One of the simplest locking devices is a locknut and these are generally thin plain nuts which are tightened against ordinary plain nuts or against components into which male threaded items are assembled. To ensure efficient locking, the bearing surfaces...

Fig Cam operated clamp

This example shows a typical assembly and includes a parts list. The balloons containing the part numbers are equally spaced whenever possible. The leader lines to the components terminate in a dot. The leader line is also directed towards the centre of the balloon and touches the circumference. It is considered good policy to position the parts list and commence writing in such a way that parts can be added on to the end of the list in the event of future modifications. The list can be drawn...

How To Buttress Thread In Engineering Drawings

Used for transmitting power in one direction only. In its original form, the pressure face now sloping at 7 was perpendicular with the thread axis. A common application of the thread can be found in workshop vices. Fig. 15.11 Buttress thread H 0.8906P, H' 0.5058P, S 0.1395P S' 0.245P. F 0.2754P. R 0.1205P Fig. 15.11 Buttress thread H 0.8906P, H' 0.5058P, S 0.1395P S' 0.245P. F 0.2754P. R 0.1205P

Scale used in geometric construction

Figure 7.16 shows the method of dividing a given line AB, 89 mm long, into a number of parts say 7 . Draw line AC, and measure 7 equal divisions. Draw line B7, and with the tee-square and set-square draw lines parallel to line B7 through points 1 to 6, to give the required divisions on AB. Fig. 7.18 Diagonal scale where 40 mm represents 1000 mm Figure 7.16 shows the method of dividing a given line AB, 89 mm long, into a number of parts say 7 . Draw line AC, and measure 7 equal divisions. Draw...

Chain dimensioning and auxiliary dimensioning

Chains of dimensions should only be used where the possible accumulation of tolerances does not endanger the function of the part. A plan view of a twist drill stand is given in Fig. 14.5 to illustrate chain dimensioning. Now each of the dimensions in the chain would be subject to a manufacturing tolerance since it is not possible to mark out and drill each of the centre distances exactly. As a test of drawing accuracy, start at the left hand side and mark out the dimensions shown in turn....

Typical example using Professor Unwins approximate construction

Module, 12 mm Number of teeth, 25. Pitch-circle diameter module x no. of teeth 12 x 25 300 mm Addendum module 12 mm Clearance 0.25 x module 0.25 x 12 3 mm Dedendum addendum clearance 12 3 15 mm Circular pitch n x module n x 12 37.68 mm Tooth thickness 1 x circular pitch 18.84 mm a Draw the pitch circle and the common tangent. b Mark out the pressure angle and the normal to the line of action. c Draw the base circle. Note that the length of the normal is the base-circle...

Conic sections and interpntration of solids

Consider a right circular cone, i.e. a cone whose base is a circle and whose apex is above the centre of the base Fig. 12.1 . The true face of a section through the apex of the cone will be a triangle. Fig. 12.1 Conic sections section AA - triangle section BB - circle section CC - parabola section DD - hyperbola section EE - rectangular hyperbola section FF - ellipse Fig. 12.1 Conic sections section AA - triangle section BB - circle section CC - parabola section DD - hyperbola section EE -...

Fig Air engine assembly illustrated below

The engine operates through compressed air entering the cylinder via one of the connecting pipes shown as item 15. The other pipe serves to exhaust the cylinder after the power stroke. The cylinder oscillates in an arc and a hole through the cylinder wall lines up with the inlet and exhaust pipes at each 180 of rotation of the flywheel. The spindles Parts 4 and 18 , grub screw Part 5 and the pin Part 11 would not normally be sectioned. A part section is illustrated at the bottom of the...

Wiring diagrams for motor vehicles

The following diagrams are reproduced by kind permission of the Ford Motor Company Ltd and show part of the wiring circuit for the Transit van. Service manuals need to be presented so that the technician can easily check each function for satisfactory operation. The manual is therefore written with each circuit shown completely and independently in one chapter or 'cell'. Other components which are connected to the circuit may not be shown unless they influence the circuit operation. For the...