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...
Reading engineering drawings
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...
Rendering controls
Presentations and proposals using photo-realistic images add excitement and visual impact. Before applying rendering features to a model, the background and lighting conditions should be adjusted to simulate mood, time and scene composition. It can also apply lighting, shadows and ray tracing for reflective and transparent materials, and if required, background scenery. Smoothing areas of high contrast to improve appearance can enhance image quality. Accuracy is improved through fully...
Socket head screws manufactured to BS EN ISO and BS
It is often required to draw these screws and although the head type and the length are generally quoted in parts lists it is necessary to know the proportions of the head. Dimensions follow for each of the most commonly used screws. Before specifying screws it is advisable to consult a manufacturers list for availability. In the interest of standardization and economy, designers are urged to use stock lengths wherever possible and standard lengths of screws include the following 3, 4, 5, 6, 8,...
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....
Mockups and prototypes
Mockups and prototypes show how products and mechanisms look and perform but building them is a time-consuming process. A 3D model is life-like, popular and can be of considerable assistance for publicity purposes especially where the client has limited technical experience. Recent developments are easy to use and an economical method of demonstrating engineering design concepts. Drawings can be communicated by email and have the advantage that they can be viewed by anyone who has a Windows PC....
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...
Case Concentricity
Product requirement To contain the centre of the large circle within a circular tolerance zone of 0.001 diameter which has its centre coincident with the datum-circle centre.
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,...
Projection exercises
It is clear to us after teaching draughting and CAD for many years that visualizing a proposed new product in three dimensions, which is how you naturally view a finished article, is difficult when it is necessary to read more than one complex two dimensional drawing simultaneously. The draughtsman also ultimately needs to produce technically correct drawings, often from vague initial ideas. The very action of making proposal drawings stimulates many questions and their answers allow...
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...
Practical application of datum targets
Interpretation It is understood from the above illustration that a Datum targets A1, A2 and A3 establish Datum A. b Datum targets B1 and B2 establish Datum B. c Datum target C1 establishes Datum C.
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...
Positional tolerancing
The essential requirement is to be able to define the limits for location of actual features, e.g. axes, points, median surfaces and nominally plane surfaces, relative to each other or in relation to one or more datum. To accurately achieve this aim, it is essential that the primary constituents, theoretically exact dimensions, tolerance zones, and datums are utilized. The tolerance zone is symmetrically disposed about its theoretically exact location. Utilizing these primary constituents...
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
Pressure angle, 20 . 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 Fig
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...
Advantages
Geometrical tolerances are used to convey in a brief and precise manner complete geometrical requirements on engineering drawings. They should always be considered for surfaces which come into contact with other parts, especially when close tolerances are applied to the features concerned. No language barrier exists, as the symbols used are in agreement with published recommendations of the International Organization for Standardization ISO and have been internationally agreed. BS 8888...
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...
Spurgear terms Fig
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...
Multiple threads
Generally, screws have single threads and unless it is designated otherwise, it is fair to assume that a thread will be single. This means that the thread is formed from one continuous helix. The lead of a thread is the distance moved by a mating nut in one complete revolution of the nut. In a single thread the lead is equal to the pitch. When a two start thread is manufactured, there are two continuous helices and to accommodate the grooves, the lead is twice the thread pitch. Multiple threads...
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...
Typical bonded joints
Figure 29.2 shows a range of bonded joints and possible modifications which can be made to reduce or eliminate the effect of cleavage and peel stresses. The following notes should be regarded as of a general nature. a Avoid butt joints if bond area is small. b Scarfed joint provides increased bonding area. c Simple lap joint with in-line forces. d Alternative lap joint with offset loading. f Bracket bonded to a fixed surface where peel is likely. g Repositioned bracket strengthens joint. h and...
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...
Machine screws
Head shapes for machine screws have been rationalized in BS EN ISO 1580 and BS EN ISO 7045. For the purpose of this British Standard, the generic term 'screws' applies to products which are threaded up to the head or having an unthreaded portion of the shank. The length of the thread is defined as the distance from the end of the screw, and this includes any chamfer, radius or cone point, to the leading face of the nut which has been screwed as far as possible onto the screw by hand. Note on...
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...