## Dimensioning for manufacture

It should be emphasized that dimensioning must be performed with the user of the drawing very much in mind. In the case of the finished bearing housing shown in Fig. 14.35 two different production processes are involved in its manufacture namely casting and machining of the component. It is sometimes preferable to produce two separate drawings, one to show the dimensions of the finished casting and the other to show the dimensions which are applicable to the actual machining operation. Figure...

## Dimensioning circles

The symbol 0 preceding the figure is used for specifying diameters and it should be written as large as the figures which establish the size, e.g. 065. Alternative methods of dimensioning diameters are given below. The size of hole and space available on the drawing generally dictates which method the draughtsman chooses.

## Methods of applying the tolerance frame to the toleranced feature

Figures 20.4 and 20.5 illustrate alternative methods of referring the tolerance to the surface or the plane itself. Note that in Fig. 20.5 the dimension line and frame leader line are offset. The tolerance frame as shown in Fig. 20.6 refers to the axis or median plane only of the dimensioned feature. Figure 20.7 illustrates the method of referring the tolerance to the axis or median plane. Note that the dimension line and frame leader line are drawn in line.

## Theoretical circuit diagrams

Design staff will prepare theoretical circuit diagrams where all the necessary connections for the correct operation of the system are included. Different sections of industry freely use other terms, such as schematics, sequence diagrams and flow charts. In all these diagrams the component parts are arranged neatly and if possible horizontally or vertically. If several diagrams form a set, then the style of presentation should be consistent. One of the conventions with this type of diagram is...

## Straight line examples

Figure 4.17 shows three components which have each been machined from solid blocks. These examples have been prepared on a grid formed by equilateral triangles. Figure 4.17 shows three components which have each been machined from solid blocks. These examples have been prepared on a grid formed by equilateral triangles. In every case, the scale is such that each side of the triangle will be 10 mm. For each component, draw five views in first angle projection, omitting hidden detail, and assume...

## Method of indicating geometrical tolerances on drawings

Geometrical tolerances are indicated by stating the following details in compartments in a rectangular frame. (a) the characteristic symbol, for single or related features (i) preceded by 0 if the zone is circular or cylindrical, (ii) preceded by S0 if the zone is spherical (c) Letter or letters identifying the datum or datum systems. Third compartment datum identification letter(s) Second compartment total tolerance value in the unit used for linear dimensions Indications qualifying the...

## Project development

The reader will appreciate that the design of, for example, a large construction project from its conception, will involve technical input from architects and engineering designers in a wide variety of associated disciplines. It is vital that all contributors to the overall scheme talk the same language and that only compatible computer software packages are in use for the separate areas of work. In addition, the management contractor must have access to the designs as work is in progress....

## Computer aided draughting and design

CAD is much more than drawing lines by electronic means. Similarly by the purchase of a CAD system, a design does not emerge at the push of a button. 'Buy a computer and you don't need a draughtsman' is also very different from reality. The engineering designer is very much responsible for decisions taken at all technical stages between conception and production. The computer is an aid and performs as it is directed with rapidity and accuracy. The following notes are included to indicate areas...

## Pneumatics and electronics

Systems of low complexity and those in use in hazardous areas, not compatible with electronics, will probably be designed as pure pneumatic systems. A purely pneumatic system can be viewed as three main sections 1 Generation and preparation of the compressed air source. 2 Power actuation of pneumatic cylinders through directional control valves. 3 Pneumatic signal processing or logic control. Electronics can influence all of these sections, for example (a) By electronic management control of...

Computing developments have made a rapid and immense impact on industry and commerce and as the degree of complexity has also increased, then training facilities have expanded accordingly. As a source of information and communication, the Technical Press and the Internet play a very important part. Journals from professional institutions offer impartial news, advice and guidance, opinions, and new product details. Manufacturers and the larger suppliers of CAD equipment have set up centres...

## The application of thread conventions

Figure 15.21(a) shows an elevation of a stud in a tapped hole. When a mating thread is screwed into a tapped hole, the section lines do not cover the assembled threads, also, the threads on the stud terminate at the start of the hole to signify that the stud is screwed to maximum depth. Adjacent parts in the sectional view are cross hatched in opposite directions. It is not normal practice to section nuts, bolts and washers. Exercise Draw a similar assembly using a M24 stud. The stud is screwed...

## Limits and fits

To ensure that an assembly will function correctly, its component parts must fit together in a predictable manner. Now, in practice, no component can be manufactured to an exact size, and one of the problems facing the designer is to decide the upper and lower limits of size which are acceptable for each of the dimensions used to define shape and form and which will ensure satisfactory operation in service. For example, a dimension of 10 0.02 means that a part will be acceptable if manufactured...

## 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

## Sheet metalwork application

The design of components to be manufactured from folded sheet metal is a field in which CAD systems can offer great assistance. In the case of the bracket shown in Fig. 3.3 it would first be necessary to establish the overall dimensions of the part. The second step would be to imagine that the bracket is folded back gradually as indicated in Fig. 3.4 into the flat sheet form. This shape would then be stamped from metal strip in a power press. The dimensions of the flat pattern have to make...

## 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...

## Tolerance zones

The width of the tolerance zone is in the direction of the leader line arrow joining the symbol frame to the toleranced feature unless the tolerance zone is preceded by the symbol 0. An example is given in Fig. 20.15a. If two tolerances are given, then they are considered to be perpendicular to each other, unless otherwise stated. Figure 20.15b shows an example. Figure 20.15c gives an example where a single tolerance zone is applied to several separate features. In the tolerance frame the...

Barber and Colman Ltd are the manufacturers of 'Shakeproof' thread-cutting screws and washers. 'Shakeproof' thread-cutting screws made from carbon steel are subjected to a special heat-treatment which provides a highly carburized surface with a toughened resilient core. The additional strength provided enables higher tightening torques to be used, and will often permit the use of a smaller-size thread-cutting screw than would normally be specified for a machine screw. Thread-cutting screws...

## End Face Run-out

The component is required to be rotated about datum axis C, with datum face B set to ensure no axial movement. The circular radial runout on the cylindrical portion must not exceed 0.05 at any point measured perpendicular to the datum axis. The circular runout on the tapered portion must not exceed 0.07 at any point measured normal to its surface. The circular runout on the curved portion must not exceed 0.04 at any point measured normal to its surface. The axial runout of the end face must not...

## Chain lines

Particular care should be taken with chain lines to ensure that they are neatly applied and attention is drawn to the following points a All chain lines should start and finish with a long dash. b When centre points are defined, then the chain lines should cross one another at solid portions of the line. c Centre lines should extend for a short distance beyond the feature unless they are required for dimensioning or other purpose. Fig. 5.3 Example showing imaginary lines of intersection Fig....

## Heating ventilation and air conditioning systems

Control systems are devised to suit each individual application. Generally, each part of the system will contain air of different types. With reference to Fig. 27.6 the room air RA is extracted by a fan, a proportion of the air is exhausted to atmosphere and the remainder Note. This diagram forms an introduction to the basic system concept highlighting the major functional areas of the overall system. It is intended for users who require a basic appreciation of the system. Note. This diagram...

## 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...

## Dimensioning holes

The depth of drilled holes, when stated in note form, refers to the depth of the cylindrical portion and not to the point left by the drill. If no other indication is given they are assumed to go through the material. Holes in flanges or bosses are generally positioned around a pitch circle PCD and may be spaced on the main centre lines of the component on centres or as shown below equally spaced off centres. Holes are usually drilled off centres to provide for maximum access to fixing bolts in...

## Interpretations of limits of size in relation to form

There are two ways of interpreting the limits of size of an individual feature, which are known by 1 The Principle of Independency, where the limits of size apply to local two point measurements of a feature regardless of form. 2 The Envelope Requirement, also known as The Taylor Principle, where the limits of size of an individual feature are intended to have a mutual dependency of size and form. Issue 1. February 1970 confirmed August 1985 Diagram to scale for 25 mm diameter f BRITISH...

## 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...

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...

## Screw threads and conventional representations

The most common application of the helix is in a screw thread which follows the path of the helix. Screw threads may be either left or right hand and these are shown pictorially in Fig. 15.1. Notice the slope of the thread and the position of the index finger on each hand. The left hand thread is used for special applications and the right hand thread is the one normally used on nuts and bolts. The thread illustrated has a vee-section. The following terms are associated with screw threads The...

## Simplified drawings

Simplified draughting conventions have been devised to reduce the time spent drawing and detailing symmetrical components and repeated parts. Figure 7.7 shows a gasket which is symmetrical about the horizontal centre line. A detail drawing indicating the line of symmetry and half of the gasket is shown in Fig. 7.8, and this is sufficiently clear for the part to be manufactured. If both halves are similar except for a small detail, then the half which contains the exception is shown with an...

## Projected toleranced zone

Figure 20.16 shows a part section through a flange where it is required to limit the variation in perpendicularity of each hole axis. The method used is to apply a tolerance to a projected zone. The enlargement shows a possible position for the axis through one hole. Each hole axis must lie somewhere within a projected cylinder of 0 0.02 and 30 deep. Note. Projected tolerance zones are indicated by the symbol . Figure 20.16 shows a part section through a flange where it is required to limit the...

## Successive sections

Figure 8.14 shows the front and end elevations of a special purpose mounting plate where sectional plans are given at different levels to illustrate the shapes of the various cutouts and details. Now it will be noted that the presentation of this problem takes considerable vertical space since all of the plan views are in correct projection. The current British Standard permits successive sections to be drawn as shown in Fig. 8.14. Figure 8.14 shows the front and end elevations of a special...

## Application of bearings

A rotating machine element, e.g. the shaft, generally requires two bearings to support and locate it radially and axially relative to the stationary part of the machine, e.g. the housing. Normally, only one of the bearings the locating bearing is used to fix the position of the shaft axially, whilst the other bearing the non-locating bearing is free to move axially. Axial location of the shaft is necessary in both directions and the locating bearing must be axially secured on the shaft and in...

## Approximate construction for nuts and bolts Figs and

1 Draw a circle in the plan position, 2D in diameter, where D is equal to the thread size. In this example let us assume that the thread size is M20. 2 Draw a hexagon inside the 40 mm diameter circle and inside the hexagon draw another circle tangential to the hexagon on the six sides. This circle is the projection of the chamfer which can be seen on the front elevation. the nut thickness is 0.8D. Project the four corners of the hexagon to the front elevation. Project three corners of the...

## Drawing modifications

After work has been undertaken on a drawing for a reasonable amount of time, then that drawing will possess some financial value. The draughtsman responsible for the drawings must be concerned with the reproducible quality of his work as prints or photographic copies are always taken from the originals. Revisions and modifications are regularly made to update a product, due for example, to changes in materials, individual components, manufacturing techniques, operating experience and other...

## Air engine

The component parts of an oscillating air engine are detailed in Fig. 18.5. Draw in first angle projection and, at twice full size, the following views a A front view taken as a section through the engine cylinder and flywheel. b A plan view in projection with the front view and drawn below the front view. c An end view on the right hand side and in projection with the front view. Hidden detail is not required in any view. Add a parts list to your drawing and reference balloons to identify each...

## Half sections

Symmetrical parts may be drawn half in section and half in outside view. This type of drawing avoids the necessity of introducing dotted lines for the holes and the recess. Dimensioning to dotted lines is not a recommended practice. Fig. 8.8 A special spanner is illustrated in Fig. 8.8. A revolved section is shown on the handle to indicate the shape of the cross section at that point. This is a convenient convention to use on single view drawings because the shape could not be confirmed without...

## 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...

## 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...

## Engineering applications

The following examples show varied uses of engineering adhesives in industry. Locking screw threads The liquid is applied to the cleaned thread of a bolt or stud. When the nut is tightened the liquid fills the gaps between mating threads and hardens to form a tough plastic joint which is shock, vibration, corrosion and leak proof. The joint will remain in place until it needs to be undone again using normal hand tools. Threadsealing pipe fittings The sealant is applied to the clean thread and...

## Fig Plug cock assembly

This example illustrates a typical industrial valve. The plug turns through 90 between the on and off positions. Spanner flats are provided and indicated by the diagonal lines. Gland packing Part 10 is supplied in rings. These rings are contained by the body cover and on assembly are fed over the plug spindle. The gland is tightened and the compressive force squeezes the packing to provide a seal, sufficient to prevent leaks, but enabling the spindle to be turned. The joint ring Part 9 is too...

## Ball and roller bearings

Each type of bearing has characteristic features which make it particularly suitable for certain applications. However, it is not possible to lay down hard and fast rules for the selection of bearing types since several factors must be considered and assessed relative to each other. The following recommendations will, for a given application, serve to indicate those details of greatest importance in deciding the type of bearing to be used. In many instances at least one of the main dimensions...

## Helical extension springs

A helical extension spring is a spring which offers resistance to extension. Almost invariably they are made from circular-section wire, and a typical selection is illustrated in Fig. 25.12. The conventional representations of tension springs are shown in Fig. 25.13 and a schematic drawing for detailing is shown in Fig. 25.14. Coils of extension springs differ from those of compression springs in so far as they are wound so close together that a force is required to pull them Fig. 25.13...

## Circular runout

Circular run-out is a unique geometrical tolerance. It can be a composite form control relating two or more characteristics, and it requires a practical test where the part is rotated through 360 about its own axis. The results of this test may include errors of other characteristics such as circularity, concentricity, perpendicularity, or flatness, but the test cannot discriminate between them. It should therefore not be called for where the design function of the part necessitates that the...

## Taper pins and parallel pins

Taper pins, with a taper of 1 in 50, and parallel pins are used on both solid and tubular sections to secure, for example, levers to torque shafts and control rods to fork ends. Some taper pins are bifurcated, or split, and the legs can be opened out for locking. Plain taper pins and parallel pins may also be locked by peening. To prevent slackness, these pins are assembled in accurate reamed holes. Undue force should not be used during the peening process or the security of the fittings may be...

## Assembly drawings

Machines and mechanisms consist of numerous parts, and a drawing which shows the complete product with all its components in their correct physical relationship is known as an assembly drawing. A drawing which gives a small part of the whole assembly is known as a sub-assembly drawing. A sub-assembly may in fact be a complete unit in itself for example, a drawing of a clutch could be considered as a sub-assembly of a drawing showing a complete automobile engine. The amount of information given...

## Maximum material condition applied to position

A typical drawing instruction is given in Fig. 22.8, and the following illustrations show the various extreme dimensions which can possibly arise. Minimum distance between hole centres and the maximum material condition of holes. Maximum distance between hole centres and maximum material condition of holes To give the same assembly condition as in A, the minimum distance between hole centres is reduced when the holes are finished away from the maximum material condition. To give the same...

## 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...

The Unified system of screw threads was introduced by the United Kingdom, Canada and the United States to provide a common standard thread for use by the three countries. The International Standards Organisation ISO recommends the system as an international system of screw threads in inch units, in parallel with a similar system in metric units. Both of these systems use a similar form of thread profile which is illustrated basically in Fig. 15.4. Fig. 15.4 Unified screw thread H 0.86603P, Rc...

## Torsion springs

Various forms of single and double torsion springs are illustrated in Fig. 25.8. Figure 25.9 gives a schematic diagram for a torsion spring. This type of drawing, adequately dimensioned, can be used for detailing. Figure 25.9 gives a schematic diagram for a torsion spring. This type of drawing, adequately dimensioned, can be used for detailing. ends of the wire in the spring may be straight, curved, or kinked.

## Worm gearing

Worm gearing is used to transmit power between two non-intersecting shafts whose axes lie at right angles to each other. The drive of a worm gear is basically a screw, or worm, which may have a single- or multistart thread, and this engages with the wheel. A singlestart worm in one revolution will rotate the worm wheel one tooth and space, i.e. one pitch. The velocity ratio is high for example, a 40 tooth wheel with a singlestart worm will have a velocity ratio of 40, and in mesh with a...

## Mech Soft

The MechSoft program contains many wizards, used to assist in the design of a large variety of mechanical solutions, which conform to National and Company Standards. The detailed component drawings are of the parametric type all are mechanically correct and used to create automatically, new components. All of these parts are compatible with the Autodesk Inventor Series. A typical small assembly is shown in Fig. 3.21. A gearbox is to be manufactured in a range of sizes using standardized...

## Maximum material condition applied to coaxiality

In the previous examples, the geometrical tolerance has been related to a feature at its maximum material condition, and, provided the design function permits, the tolerance has increased when the feature has been finished away from the maximum material condition. Now the geometrical tolerance can also be specified in relation to a datum feature, and Fig. 22.13 shows a typical application and drawing instruction of a shoulder on a shaft. The shoulder is required to be coaxial with the shaft,...

## Keys and keyways

A key, Fig. 17.1, is usually made from steel and is inserted between the joint of two parts to prevent relative movement it is also inserted between a shaft and a hub in an axial direction, to prevent relative rotation. A keyway, Figs. 17.2, 17.3 and 17.4, is a recess in a shaft or hub to receive a key, and these recesses are commonly cut on key-seating machines or by broaching, milling, planing, shaping and slotting. The proportions of cross-sections of keys vary with the shaft size, and...

## Dimensioning principles

A drawing should provide a complete specification of the component to ensure that the design intent can be met at all stages of manufacture. Dimensions specifying features of size, position, location, geometric control and surface texture must be defined and appear on the drawing once only. It should not be necessary for the craftsman either to scale the drawing or to deduce dimensions by the subtraction or addition of other dimensions. Double dimensioning is also not acceptable. Theoretically...

## 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....

## Product development and computer aided design

Work undertaken by a drawing office will vary considerably with different branches of industry. Generally, work of a 'design and make' nature will follow a plan which sets out stages in development from the time a potential client makes an enquiry until the completed product is delivered. The function of the product will dictate many of the associated activities. A vehicle manufacturer will not design and make all of the parts used but subcontract components from specialists. The engine...

## Cam followers

Various types of cam followers are shown in Fig. 24.1. Knife-edge followers are restricted to use with slow-moving mechanisms, due to their rapid rates of wear. Improved stability can be obtained from the roller follower, and increased surface area in contact with the cam can be obtained from the flat and mushroom types of follower. The roller follower is the most expensive type, but is ideally suited to high speeds and applications where heat and wear are factors. Fig. 24.1 Plate cams a Plate...

## Machine drawing

The draughtsman must be able to appreciate the significance of every line on a machine drawing. He must also understand the basic terminology and vocabulary used in conjunction with machine drawings. Machine drawings of components can involve any of the geometrical principles and constructions described in this book and in addition the accepted drawing standards covered by BS 8888. Figure 7.15 illustrates many features found on machine drawings and the notes which follow give additional...

The following notes and illustrations are intended to assist in reading and understanding simple drawings. In all orthographic drawings, it is necessary to project at least two views of a three dimensional object - or one view and an adequate description in some simple cases, a typical example being the drawing of a ball for a bearing. A drawing of a circle on its own could be interpreted as the end elevation of a cylinder or a sphere. A drawing of a rectangle could be understood as part of a...

## 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....

## 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...

## Requirements

Figure 14.43 shows mandatory positions of associated surface texture requirements. Note that in accordance with BS EN ISO 1302 2002 the position 'X' is no longer used. Only positions a, b, c, d and e should be used. Position 'a' indicates one single surface texture requirement. Positions 'a' and 'b' indicate two or more surface texture requirements. Position 'c' indicates manufacturing method, treatment, coating or other process. Position 'd' indicates surface lay. Position 'e' shows machining...

## Disc springs

For bolted connections a very simple form of compression spring utilizes a hollow washer manufactured from spring steel, although other materials can be specified. Table 25.1 shows a selection of Belleville washers manufactured to DIN 6796 from spring steel to DIN 17222. If the disc has its top and bottom surfaces ground to approximately 95 of the appropriate thickness in the table above then bearing surfaces will be formed. These surfaces improve guidance where several discs are used together....

## 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...

## Isometric projection

Figure 6.1 shows three views of a cube in orthographic projection the phantom line indicates the original position of the cube, and the full line indicates the position after rotation about the diagonal AB. The cube has been rotated so that the angle of 45 between side AC1 and diagonal AB now appears to be 30 in the front elevation, C1 having been rotated to position C. It can clearly be seen in the end view that to obtain this result the angle of rotation is greater than 30 . Also, note that,...

## Locking plates

Locking plates are manufactured usually from mild steel and fit over hexagonal nuts after these have been tightened on assembly. The locking plate is then secured on the component by a separate screw which may itself be fitted with a shakeproof or spring type of washer. Locking plates may be used repeatedly, provided they remain a good fit, around the hexagon of the nut or the bolthead. Locking plates may be cranked, as in Fig. 16.28 or flat. Figure 16.29 shows a selection of locking terminals...

## 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...

## Oblique projection

Figure 6.8 shows part of a plain bearing in orthographic Fig. 6.3 Construction principles for points in space, with complete solution Figure 6.8 shows part of a plain bearing in orthographic Fig. 6.3 Construction principles for points in space, with complete solution Fig. 6.4 Views b , c and d are isometric projections of the section in view a Fig. 6.4 Views b , c and d are isometric projections of the section in view a Fig. 6.6 Isometric constructions for corner radii Fig. 6.6 Isometric...

## Split cotter pins

Ferrous and non ferrous split cotter pins are covered by BS 1574. The designating size of a split cotter pin is the size of the hole for which it is intended to fit. When reference is made to a split cotter pin in a parts list, this nominal dimension is followed by the length required. The closed legs of the shank of the pin form a circular cross section. The legs should be straight and parallel throughout their nominal length. Figure 16.32 shows alternative pins in detail. Alternative shape of...

## Plain bearings

Plain bearings may be classified as follows Plain bearings a Solid inserts b Lined inserts c Wrapped ii Medium walled insert liners iii Thin walled insert liners. The bearing metal should have a low coefficient of sliding friction, be able to conduct heat generated away from the bearing surfaces, resist wear in use and be tough enough to withstand shock loading in service. In the event of breakdown due to lack of lubrication, it may be desirable when overheating occurs for the bearing material...

## Cams and gears

A cam is generally a disc or a cylinder mounted on a rotating shaft, and it gives a special motion to a follower, by direct contact. The cam profile is determined by the required follower motion and the design of the type of follower. The motions of cams can be considered to some extent as alternatives to motions obtained from linkages, but they are generally easier to design, and the resulting actions can be accurately predicted. If, for example, a follower is required to remain stationary,...

## 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...

## 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...

## General engineering graphical symbols

Construction Drawing Series lists the following Part 1 - Buildings and parts of buildings Part 2 - Room names and numbers Part 3 - Room identifiers BS EN ISO 6284 Indication of Limit Deviations BS EN ISO 8560 Representations of modular sizes, lines and grids BS EN ISO 9431 Spaces for drawing for text and title block on drawing BS EN ISO 3766 Simplified representation of concrete reinforcement BS EN ISO 7518 Simplified representation of demolition and rebuilding BS EN ISO 11091 Landscape drawing...

## Profile tolerance of a surface

Profile tolerance of a surface is used to control the ideal form of a surface, which is defined by theoretically exact boxed dimensions and must be accompanied by a relative tolerance zone. The profile-tolerance zone, unless otherwise stated, is taken to be bilateral and equally disposed about its true-form surface. The tolerance value is equal to the diameter of spheres whose centre lines lie on the true form of the surface. The zone is formed by surfaces which touch the circumferences of the...

## The involute

The involute is defined as the path of a point on a straight line which rolls without slip along the circumference of a cylinder. The involute curve will be required in a later chapter for the construction of gear teeth. 1 Draw the given base circle and divide it into, say, 12 equal divisions as shown in Fig. 10.8. Generally only the first part of the involute is required, so the given diagram shows a method using half of the length of the circumference. 2 Draw tangents at points 1, 2, 3, 4, 5...

## Typical product requirement

In the example shown in Figs 23.2 and 23.3, the hole axis must lie within the cylindrical tolerance zone fixed Some advantages of using this method are 1 interpretation is easier, since true boxed dimensions fix the exact positions of details 2 there are no cumulative tolerances 3 it permits the use of functional gauges to match the mating part 4 it can ensure interchangeability without resorting to small position tolerances, required by the coordinate tolerancing system 5 the tolerancing of...

## 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...

## Dimensioning of welds

The dimensions of a weld may be added to a drawing in the following manner. Dimensions relating to the cross section of the weld are symbolized by b and are given on the left-hand side of the symbol. The cross-sectional dimension to be indicated for a fillet weld is the leg length. If the design throat thickness is to be indicated then the leg-length dimension is prefixed with the letter b and the design throat thickness with the letter a. Longitudinal dimensions are symbolized by l and are...

## International Organization for Standardization ISO

ISO is made up of national standards institutes from countries large and small, industrialized and developing, in all regions of the world. ISO develops voluntary technical standards, which add value to all types of business operations. They contribute to making the development, manufacturing and supply of products and services more efficient, safer and cleaner. They make trade between countries easier and fairer. ISO standards also serve to safeguard consumers, and users in general, of...

## Parametric design

It is a common drawing office practice, where a range of parts are similar, to produce a single drawing with a table of dimensions for the features of each separate component. The user will then need to sort out the appropriate sizes of each detail relating to the part required. The drawing itself being representative of a number of similar parts cannot be drawn true to scale for them all. A study of Fig. 3.1 will show a special screw, which has a family of parts. It is defined on a single...

## The psychrometric chart

In air conditioning technology, it is necessary to define thermodynamic processes and the properties of moist air. This may be achieved by a good knowledge of physics, with theoretical calculations using complicated formulae and tables. The procedure can be time consuming. By presenting the interrelated factors on a psychrometric chart, an immediate decision can be made regarding the feasibility of controlling an air conditioning system and the means required to carry this out. For a given air...

## The application of welding symbols to working drawings

The following notes are meant as a guide to the method of applying the more commonly used welding symbols relating to the simpler types of welded joints on engineering drawings. Where complex joints involve multiple welds it is often easier to detail such constructions on separate drawing sheets. Each type of weld is characterized by a symbol given in Table 26.1 Note that the symbol is representative of the shape of the weld, or the edge preparation, but does not indicate any particular welding...

## Bevelgear terms and definitions

The following are additions to those terms used for spur gears. A addendum B dedendum C cone distance D pitch diameter Da outside diameter Dr root diameter E bottom clearance F face width a alpha addendum angle beta dedendum angle Y gamma pitch angle Ya back cone angle A addendum B dedendum C cone distance D pitch diameter Da outside diameter Dr root diameter E bottom clearance F face width a alpha addendum angle beta dedendum angle Y gamma pitch angle Ya back cone angle The pitch angle is the...

## Leaf springs

The two standards applicable to leaf springs are shown in Fig. 25.11. These springs are essentially strips of flat metal formed in an elliptical arc and suitably tempered. They absorb and release energy, and are commonly found applied to suspension systems. Fig. 25.11 a and b conventional and simplified representations for a semi-elliptic leaf spring c and d conventional and simplified representations for a semi-elliptic leaf spring with fixing eyes Fig. 25.11 a and b conventional and...

## Simmonds locknut

This type of locknut incorporates a collar manufactured from nylon or fibre and the collar is slightly smaller in diameter than the internal thread diameter. The section in Fig. 16.23 shows the collar in black. On assembly, the stud or bolt forces its way through the resilient collar which provides a frictional lock. The locknut is a little thicker than a conventional nut.

## Pneumatic systems

Pneumatic systems require a supply of clean compressed air to motivate cylinders, tools, valve gear, instruments, delicate air controls and other equipment. Most factory and plant installations operate between 5.5 and 7 bar. A typical compressor installation is shown in Fig. 27.23. Compressors are sized according to the amount of free air delivered. Air flow is measured in cubic decimetres per second dm3 s at standard atmospheric conditions of 1013 mbar and 20 C as specified in ISO 554. The...

## Cam follower motions

1 Uniform velocity This motion is used where the follower is required to rise or fall at a constant speed, and is often referred to as straight-line motion. Part of a uniform-velocity cam graph is shown in Fig. 24.2. Abrupt changes in velocity with high-speed cams result in large accelerations and cause the followers to jerk or chatter. To reduce the shock on the follower, the cam graph can be modified as indicated in Fig. 24.3 by adding radii to remove the sharp corners. However, this action...

## Production drawings

The following three typical drawings are included as examples of draughtsmanship, layout, dimensioning, and tolerancing. Figures 31.1 and 31.2 show a pulley and a shaft, and illustrate some aspects of general dimensioning and tolerancing. Figure 31.3 shows a partly dimensioned elevation and plan view of a proposed gear-box cover, with a wide application of theoretically exact boxed dimensioning and the associated positional tolerances. To emphasize this style of dimensioning, other dimensions...

## Spur Gear Drawing

The gear ratio is the ratio of the number of teeth in the gear to the number of teeth in the pinion, the pinion being the smaller of the two gears in mesh. The pitch-circle diameters of a pair of gears are the diameters of cylinders co-axial with the gears which will roll together without slip. The pitch circles are imaginary friction discs, and they touch at the pitch point. The base circle is the circle from which the involute is generated. The root diameter is the diameter at the base of the...

## Case Coaxiality

Product requirement To contain the axis of the Datum axis central cylinder within a cylindrical tolerance zone which is coaxial with the mean axes of the left- and right-hand cylinders. Product requirement To contain the axis of the right-hand cylinder within a cylindrical tolerance zone which is coaxial with the axis of the datum cylinder. Product requirement To contain the axes of both the left- and right-hand cylinders within a cylindrical tolerance zone.

## Methods of specifying datum features

A datum is designated by a capital letter enclosed by a datum box. The box is connected to a solid or a blank datum triangle. There is no difference in understanding between solid or blank datum triangles. Fig. 20.18 and Fig. 20.19 show alternative methods of designating a flat surface as Datum A. Figure 20.20 illustrates alternative positioning of datum boxes. Datum A is designating the main outline of the feature. The shorter stepped portion Datum B is positioned on an extension line, which...

## Bevel gears

If the action of spur and helical gears can be related to that of rolling cylinders, then the action of bevel gears can be compared to a friction cone drive. Bevel gears are used to connect shafts which lie in the same plane and whose axes intersect. The size of the tooth decreases as it passes from the back edge towards the apex of the pitch cone, hence the cross-section varies along the whole length of the tooth. When viewed on the curved surface which forms part of the back cone, the teeth...

## 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...

## Selected ISO fitshole basis extracted from BS

The ISO system provides a great many hole and shaft tolerances so as to cater for a very wide range of conditions. However, experience shows that the majority of fit conditions required for normal engineering products can be provided by a quite limited selection of tolerances. The following selected hole and shaft tolerances have been found to be commonly applied selected hole tolerances H7 H8 H9 H11 selected shaft tolerances c11 d10 e9 f7 g6 h6 k6 n6 p6 s6. Table 19.1 shows a range of fits...

## Toolbox

The details in Fig. 18.6 show parts of a toolbox which can be made as a sheet-metal-work exercise. A development is given of the end plates two required and these should be drilled at the corners before bending, to avoid possible cracking taking place. Note, from the photograph, that the ends have been pressed with grooves to provide additional stiffening and this can be done if facilities are available. The bottom and sides are fabricated in one piece and drillings are shown for pop rivets....

## General engineering graphical symbol series

BS 1553 Specification for graphical symbols for general engineering. Part 1 Piping systems and plant. This section deals with graphical symbols for use in the creation of flow and piping plant and heating and ventilation installations. Part 2 Graphical symbols for power generating plant. Includes steam and internal combustion engines and turbines, also auxiliary plant. Part 3 Graphical symbols for compressing plant. Includes applications to air operated switchgear. Fluid Power Systems and...

## Maximum material condition applied to squareness

Figure 22.5 shows a typical drawing instruction where limits of size are applied to a pin, and in addition a squareness tolerance of 0.3 is applicable at the maximum material condition. Figure 22.6 shows the condition where the pin is finished at the maximum material condition with the maximum squareness error of 0.3. The effective assembly diameter will be the sum of the upper limit of size and the squareness error. The squareness error will be contained within a cylindrical tolerance zone of...

## 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...

## Lines and linework

Two thicknesses of line are recommended for manual and CAD drawings. A wide line and a narrow line in the ratio of 2 1. Standard lead holders, inking pens for manual use, and those for CAD plotters are all available in the following millimetre sizes 0.25, 0.35, 0.5, 0.7, 1.0, 1.4 and 2.0. Line thicknesses of 0.7 and 0.35 are generally used and will give good quality, black, dense and contrasting lines. Table 5.2, shows applications for different line types which are designed to obtain a good...

## Dimensioning cams

Figure 24.12 shows a cam in contact with a roller follower note that the point of contact between the cam and the roller is at A, on a line which joins the centres of the two arcs. To dimension a cam, the easiest method of presenting the data is in tabular form which relates the angular displacement 0 of the cam with the radial displacement R of the follower. The cam could then be cut on a milling machine using these point settings. For accurate master cams, these settings may be required at...