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...
Designing for adhesives
For the best possible performance, joints should be specifically designed for adhesive bonding. Follow this principle and much better joints will be achieved than if bonding is adopted as a substitute for welding in a joint designed for that purpose. Bond stresses, materials, type of adhesive, surface preparations, method of application and production requirements can then all be considered in relation to each other at the outset. The designer should consider especially the effect of shear,...
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...
Threadcutting screws
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...
Case Xmq
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...
Interchangeable systems Fig
Fig. 19.9 Elements of interchangeable systems Fig. 19.9 Elements of interchangeable systems Nominal size is the size by which a component is referred to as a matter of convenience, i.e. 25 mm, 50 Basic size is the size in relation to which all limits of size are fixed, and will be the same for both the male Limits of size These are the maximum and minimum permissible sizes acceptable for a specific dimension. Tolerance This is the total permissible variation in the size of a dimension, and is...
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...
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...
Typical AutoCAD drawings
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...
Dimensioning spotfaces
Countersinking is also carried out on a drilling machine, and Fig. 14.30 shows typical tools. Included angles of Spotfacing is a similar operation to counterboring, but in this case the metal removed by the tool is much Fig. 14.30 b Straight-shank machine countersink with 60 or 90 included angle of countersink Fig. 14.33 Fig. 14.30 b Straight-shank machine countersink with 60 or 90 included angle of countersink Fig. 14.33 less. The process is regularly used on the surface of castings, to...
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...
Technical product documentation
Individual companies generally develop their own systems largely depending on the type of work involved and the size of the undertaking, e.g. original designs, drawing revisions, modifications, repairs, new contracts, enquiries and proposals. These notes provide guidelines for new business routines where both manual and computer based systems are used. They refer to internal communication within companies and between other organizations. There are five short Standards dealing with the handling...
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...
Lubrication
Grease lubrication is generally used where ball and roller bearings operate at normal speeds, temperature and loading conditions. Grease has certain advantages by comparison with oil it is more easily retained in the bearing housing and assists in sealing against the entry of dirt and moisture. In general the free space in the bearing and housing should only be partly filled with grease 30 to 50 . Overfilling causes rapid temperature rise particularly if speeds are high. Manufacturers supply...
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...
Plug cock
Details of a plug cock are shown in Fig. 18.4. Draw the following two views of the assembled plug cock a A view in half section showing the outside view on the left of the vertical centre line and a section on the right hand side, the position of the valve body being similar to that shown on the given detail. Add a title and a parts list. Hidden details are not required in either view. Include on your assembly suitable nuts and bolts and washers where applicable. Between the valve body and...
Maximum material condition related to geometrical form
The limit of size, together with geometrical form or position of a feature, are factors of the maximum material principle, and its application is restricted to those features whose size is specified by toleranced dimensions incorporating an axis or median plane. It can never be applied to a plane, surface, or line on a surface. The characteristics to which it can be applied are as follows The characteristics to which the maximum material condition concept cannot be applied are as follows...
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...
Involute gear teeth proportions and relationships
Number of teeth, T Circular pitch n x module Addendum module Clearance 0.25 x module Dedendum addendum clearance Involute gears having the same pressure angle and module will mesh together. The British Standard recommendation for pressure angle is 20 . The conventional representation of gears shown in Fig. 24.16 is limited to drawing the pitch circles and outside diameters in each case. In the sectional end elevation, a section through a tooth space is taken as indicated. This convention is...
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 Fig
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...
Unified threads
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...
MechSoft
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...
