Variation of features

Straightness Flat Surface

No feature on a component can be perfect. No surface can be perfectly flat, no hole can be perfectly round, no two perpendicular surfaces can be at exactly 90 . The reason for this is that all manufacturing processes are variable to a greater or lesser degree and thus, all features have an inherent variability. During any type of manufacture of, say, a flat surface, there will be variability inherent within the manufacturing process caused by vibrations, inequalities, instabilities and wear....

Fit types and categories

Clearance fits can be subdivided into running or sliding fits. Running applies to a shaft rotating at speed within a journal whereas sliding can be represented by slow translation, typically of a spool valve. Running and sliding fits are intended to provide a similar running performance with suitable lubrication allowance throughout a range of sizes. Transition fits are used for locational purposes. Because of the difference in sizes they will either be low clearance fits or low interference...

Roughness and waviness

A trace across a surface provides a profile of that surface which will contain short and long wavelengths see Figure 4.11 . In order for a surface to be correctly inspected, the short and long wavelength components need to be separated so they can be individually analysed. The long waves are to do with dimensions and the short waves are to do with the SF. Both can be relevant to function but in different ways. Consider the block in Figure 6.1. This has been produced on a shaping machine. The...

The danger of visual illusions

Visual Illusions

Engineering drawing is based on the fact that three-dimensional objects are presented in a two-dimensional form on two-dimensional paper. The potential problems of trying to convey apparent three-dimensional information on two-dimensional flat paper is shown by the two sets of circles in Figure 1.2. The author drew these 12 circles himself, and they are based on a concept by Ramachandran 1988 . Because the circles are shaded, each one is seen as either a bump or a depression. In this case, if...

The shaft basisand the hole basissystem of fits

Clearance Transition And Interference

In all the examples given above, the discussion has been concerning 'shafts' and 'holes'. It should be remembered that this does not necessarily apply to shafts and holes. These are just generic terms that mean anything that fits inside anything else. However, whatever the case, it is often the case that either the shaft or the hole is the easier to produce. For example, if they are cylindrical, the shaft will be the more easily produced in that one turning tool can produce an infinite number...

Tolerancing dimensions

There are essentially two methods of adding tolerances to dimensions firstly universal tolerancing and secondly specific tolerancing. In the universal tolerance case, a note is added to the bottom of the drawing which says something like 'all tolerances to be 0.1mm'. This means that all the features are to be produced to their nominal values and the variability allowed is plus or minus 0,1mm. However, such a blanket tolerance is unlikely to apply to each and every dimension on a drawing since...

Representation visualization and specification Representation and visualization

An artefact or system can be represented in a variety of ways. Engineering drawing is but one of the ways. Figure 1.7 shows some of the ways that products or systems can be represented. Verbal or written instructions take the form of words describing something. If the words take the form of a set of instructions for doing something, they are ideal. If the words are used to tell a story, then they can paint beautiful pictures in the imagination. However, Imagined and variable Defined and having...

Iti Engineering Drawing

Iti Engineering Drawing Third Angle View

True or false Answers will be found in the text or in the figures in Chapter 2. 3D engineering drawings should always be completed in perspective projection. Axonometric projection is a particular type of isometric projection. The best pictorial projection is isometric projection. Cavalier projection is to be preferred to Cabinet projection. Third angle projection is to be preferred to first angle. Projection lines need to be included on engineering drawings. A sectional view of a part...

Sectional views

Sectioning Engineering Drawing

There are some instances when parts have complex internal geometries and one needs to know information about the inside as well as the outside of the artefact. In such cases, it is possible to include a section as one of the orthographic views. A typical section is shown in Figure 2.16. This is a drawing of a cover that is secured to another part by five bolts. These five bolts pass through the five holes in the edge of the flange. There is an internal chamber and some form of pressurised...

Surface finish characterization

Abbott Firestone Curve

Once a satisfactory profile is obtained, it can be analysed and represented by a variety of means. This raises the question of what particular number, parameter or descriptor should be used. Unfortunately, there is no such thing as a universal parameter or descriptor and one must select from the ones published in the ISO standards. With reference to Figure 6.5, the ADF Amplitude Distribution Function or height distribution function is a histogram where the value of p y represents the fraction...

Requirements of engineering drawings

Engineers Vice Orthographic Drawing

Engineering drawings need to communicate information that is legally binding by providing a specification. Engineering drawings therefore need to met the following requirements Engineering drawings should be unambiguous and clear. For any part of a component there must be only one interpretation. If there is more than one interpretation or indeed there is doubt or fuzziness within the one interpretation, the drawing is incomplete because it will not be a true specification. The drawing must be...

Leader lines

A leader line is a line referring to some form of feature that could be a dimension, an object or an outline. A leader line consists of two parts. These are A type B line thin, continuous, straight going from the instruction to the feature. A terminator. This can be a dot if the line ends within the outline of the part, an arrow if the line touches the outline or centre line of a feature or without either an arrowhead or a dot if the line touches a dimension. Examples of leader lines with...

Symbology

Step Weld Symbol

The ISO standards recommend that abbreviations and symbols are used wherever possible to avoid a link to any particular language. Examples of the use of symbology and English language abbreviations are as follows BS 8888 2000 ' lt ' or 'DIA' or 'D' or'd' diameter 'n' arc 'CL' centre line 'CRS' centres 'CSK' countersunk 'CYL' cylinder 'DRG' drawing 'HEX' hexagonal 'MMC' maximum material condition 'PCD' pitch circle diameter 'R' or 'RAD' radius 'SP' spherical diameter 'SQ' or a small square a...

3rd Angle Projection

Nut Bolt Third Angle Drawing

True or false All answers will be found in the text or in the figures in Chapter 3. The ISO type A' and 'B' line thicknesses should be in the proportion 1 2. The ISO line type A' is the most critical. The line types 'C' and 'D' are interchangeable. Cross hatch lines are at 45 wherever possible. Sections are always cross hatched, irrespective of the size or length of the section. It is not necessary to have a terminator at the end of a leader line. Dimension projection lines do not always...

Oblique projection

Oblique Engineering Drawings

In oblique projection, the object is aligned such that one face the front face is parallel to the picture plane. The projection lines are still parallel but they are not perpendicular to the picture plane. This produces a view of the object that is 3D. The front face is a true view see Figure 2.7 . It has the advantage that features of the front face can be drawn exactly as they are, with no distortion. The receding faces can be drawn at any angle that is convenient for illustrating the shape...

Of Abbreviations

ADF amplitude distribution function ANSI American National Standards Institute BSI British Standards Institution CDF cumulative distribution function DIN Deutsches Institut f r Normung EDM electro-discharge machining ISO International Standards Organisation SEM scanning electron microscope Introduction List of Symbols List of Abbreviations 1 Principles of Engineering Drawing 1 4 Dimensions, Symbols and Tolerances 65 5 Limits, Fits and Geometrical Tolerancing 88 6 Surface Finish Specification...

Unacceptable dimensioning practice

Incorrect Dimensioning

It is a fundamental principle of dimensioning that the part and its dimensioning should be separated so that one does not impinge on the other and cause confusion. Such an example of incorrect dimensioning practice is shown in Figure 4.7. This is a plate with two circular holes and two rectangular holes in it. The various incorrect practices are shown by the word 'Wrong'. These are dimension lines being within the outline of the part, dimension lines crossing, broken extension lines, extension...

Surface finish specification in the real world

When it comes to drawing a part to be manufactured for real, it is not necessary to add an SF specification to each and every feature. The vast majority of features do not need them since the common manufacturing processes achieve the SF required and more often than not, the SF is unimportant. It is only in a few instances, where a surface is functionally important, that it is necessary to define a SF. Indeed, specifying a SF is the exception rather than the rule and I have seen many drawings...

Flats on cylindrical or shaped surfaces

Iso 6410 Thread

It is not always obvious that surfaces are flat when they are on otherwise curved, cylindrical or spherical surfaces. In this case, flat surfaces such as squares, tapered squares and other flat surfaces may be indicated by thin 'St Andrew' cross type diagonal lines. An example of this is shown in the entirely fictitious gear shaft in Figure 3.17. The extreme right-hand end of the shaft has a reduced diameter and approximately half of this cylindrical length has been flat milled to produce a...

Dimension lines

Dimensioning Lines Engineering

Various ISO standards are concerned with dimensioning. They are under the heading of the ISO 129 series. The basic standard is ISO 129 1985 but it has various parts to it. A dimensioning 'instruction' must consist of at least four things. Considering the 50mm width of the jaw and the 32mm spacing of the holes of the movable jaw drawing in Figure 3.15, these are Two projection lines which extend from the part and show the beginning and end of the actual dimension. They are projected from the...

Sectioning or crosshatching lines

When you go to a museum, you often see artefacts that have been cut up. For example, to illustrate how a petrol engine works, the cylinder block can be cut in half and the cut faces are invariably painted red. In engineering drawing, cross-hatching is the equivalent of painting something red. It is used to show the internal details of parts which otherwise would become too complex to show or dimension. The cross-hatch lines are usually equi-spaced and, for small parts, cover the whole of the...

Nbm Engineering Sample Drawings

Angle Projection Engineering Drawing

True or false All answers can be found in the text or in the figures in Chapter 5. The clearance in a 'close-running fit' is smaller than that in a There is no out-of-roundness in a hole drilled by a new sharp drill. The IT5 tolerance range is larger than the IT4 tolerance ranee. One of the values of the 'H' or 'h' tolerance classes is always zero. The tolerance class c 11 is the negative of class C11. The GT symbol for symmetry is an 'equals' sign. A datum must always be given in a GT box....

General

Engineering Drawing Belt Pulley

Figures 3.2 and 3.3 are detail drawings of the movable jaw and the hardened inserts respectively. Using the dimensional information in these figures and scaled measurements from the assembly drawing in Figure 3.1, draw detail drawings in third angle projection of the other parts. Include dimensions and tolerances. Also include geometric tolerances and surface finish specifications where you think appropriate. These are the body part 1 , the bush part 4 , the bush screw part 5 , the jaw...

Why are first and third angle projections so named

First Angle And Third Angle

The terms first angle projection and third angle projection may seem like complicated terms but the reason for their naming is connected with geometry. Figure 2.15 shows four angles given by the planes OA, OB, OC and OD. When a part is placed in any of the four quadrants, its outline can be projected onto any of the vertical or horizontal planes. These projections are produced by viewing the parts either from the right-hand side or from above as shown by the arrows in the diagram. In first...

First Angle Projection

First Angle Projection

Figure 2.13 First angle projection of a bracket First angle projection is becoming the least preferred of the two types of projection. Therefore, during the remainder of this book, third angle projection conventions will be followed. In third angle projection, the various views are projected from each other. Each view is of the same size and scale as the neighbouring views from which it is projected. Projection lines are shown in Figure 2.14. Here only three of the Figure 2.12 views are shown....

Manual and machine drawing

Drawings can be produced by man or by machine. In the former, it is the scratching of a pencil or pen across a piece of paper whereas in the latter, it is the generation of drawing mechanically via a printer of some type. In manual drawing, the various lines required to define an artefact are drawn on paper, using draughting equipment. The draughting equipment would typically consist of a surface to draw on, pens or pencils to draw with and aids like set-squares and curves to draw around. A...

Number of views

In the examples of the cornflake packet shown in Figure 2.11 and the small bracket shown in Figure 2.12, six views of each component were shown. There can only ever be six views of an artefact in a full orthographic projection. The central view is invariably the front view. Other views can be included but these will be auxiliary views. Such auxiliary views are placed remote from the orthographic views. If an artefact contains a sloping surface, the true view of the inclined surface will never...

Isometric projection

Bracket Isometric

In isometric projection, the projection plane forms three equal angles with the co-ordinate axis. Thus, considering the isometric cube in Figure 2.4, the three cube axes are foreshortened to the same amount, i.e. AB AC AD. Two things result from this, firstly, the angles a b 30 and secondly, the rear hidden corner of the cube is coincident with the upper corner corner D . Thus, if the hidden edges of the cube had been shown, there would be dotted lines going from D to F, D to C and D to B. The...

Tolerances applied to the assessment of surface finish

The SL sets the limits for the horizontal length to be considered along the surface. By definition, there also needs to be limits defined in the other direction the vertical . This defines the deviation allowed perpendicular to the surface. This will be the SF tolerance. Like any length dimension, the SF tolerance needs to be in the form of a tolerance band or range within which the 2D parameter may vary. There are two types of tolerance. Firstly, there is an upper one that the measured value...

Chain Dimensioning

Engineering Drawing Dimensions

The drawing page and into the eye of the reader. The valve dimensions follow the dimensioning convention laid down in the future ISO 129-1 2003 standard. Tolerances have been left off the figure for convenience. In this case there are two datum features. The first is the left-hand annular face of the largest cylindrical diameter, i.e. the face with the 30 chamfer. Horizontal dimensions associated with this datum face use a terminator in the form of a small circle. The other datum feature is the...

Geometric tolerance classes

Example Engineering Symbol Concentricity

The table in Figure 5.13 has shown the various classes of geometrical tolerance. These are only a selection of the most commonly used ones. The full set is given in ISO 1101 2002. Row 1 in the table in Figure 5.13 refers to 'GTs of straightness'. The symbol for straightness is a small straight line as is seen in the final column of the table. An example of straightness is seen in Figure At the periphery of the section, run-out is not to exceed 0,15 measured normal to the toleranced surface over...

Limits and fits

Iso Limits And Fits

The tolerance ranges shown in Figures 5.4, 5.5 and 5.6 are simply ranges. To relate to function they must be put into context and related to some absolute datum. This is the situation demonstrated by the bearings in Figure 5.1. Considering the 'close-running fit' example, the tolerance ranges are IT8 for the hole and IT7 for the shaft. However, it is insufficient to just quote an IT tolerance class on its own. The tolerance class must be related to a datum, in this case the nominal 20mm...

Splines and serrations

Splines and serrations are repetitive features comparable to screw threads. Similarly, it is not necessary to give all the details of the splines or serrations, the symbology does it for you. The convention is that one line represents the crests of the serrations or splines and the other the roots. This is shown in the hypothetical drawing in Figure 3.17 where there is a spline at the right-hand end of the gear drive shaft. A note would give details of the spline. The standard ISO 6413 1988...

Line types and thicknesses

The standard ISO 128 1982 gives 10 line types that are defined A to K excluding the letter I . The table in Figure 3.4 shows these lines. Material medium carbon steel. All dimensions in mm. Figure 3.3 Detailed engineering drawing of the 'hardened insert', part number 2 Material medium carbon steel. All dimensions in mm. Figure 3.3 Detailed engineering drawing of the 'hardened insert', part number 2 The line types are 'thick', 'thin', 'continuous', 'straight', 'curved', 'zigzag', 'discontinuous...

Geometry and tolerances

Geometric Tolerance Symbols

In many instances the geometry associated with tolerances is of significance and the geometry itself needs to be defined by tolerances such that parts fit, locate and align together correctly. Tolerances must therefore also apply to geometric features. The table in Figure 5.13 shows the commonly used geometric tolerance GT classes and symbols. These are a selection from ISO 1101 2002. The use of geometric tolerances is shown by three specific examples that are discussed in detail in the...

Perspective projection

Trimetric Projection

Perspective projection is as shown in Figure 2.2. Perspective projection is reality in that everything we see in the world is in perspective such that the objects always have vanishing points. Perspective projection is thus the true view of any object. Hence, we use expressions like 'putting something in perspective' Projectors radiate from a station point i.e. the eye past the object and onto the 2D picture plane. The station point is the viewing point. Although there is only one station...

ISO tolerance ranges

Tolerance bands need to be defined which can be related to functional performance and manufacturing processes. The ISO has published tolerance ranges to help designers. Examples of these tolerance ranges are shown in Figure 5.4. This table is only a selection from the full table given in ISO 286-2 1988. The full range goes up to IT18 and 3m nominal size. The tolerance ranges are defined by 'IT' ranges as shown in the diagram from IT1 to IT11. The range given in the ISO standard is significantly...

Relationship to functional performance

How Show Tolerance Drawing

A journal bearing in a car engine is a convenient example of the necessity of carefully defining tolerances. If a journal bearing is designed to operate at high rotational speeds, the diamentral clearance is very important. If the clearance is too small, the bearing will seize whereas if the clearance is too large, the journal will vibrate within the bearing, creating noise, wear, vibration and heat. There is therefore an optimum clearance which is associated with smooth running. However,...

Sample length and evaluation length

Hommelwerke

Considering the case of a flat surface, the traverse unit drives the stylus over a distance called the evaluation length EL . This length is Figure 6.2 A scanning electron microscope photograph of a stylus courtesy of Hommelwerke GmbH Figure 6.2 A scanning electron microscope photograph of a stylus courtesy of Hommelwerke GmbH divided into five equal parts, each of which is called a sampling length SL . In ISO 4287 1997, the sample length is defined as the 'length in the direction of the X-axis...

Functional and nonfunctional dimensions

Although every aspect of a component has to be dimensioned, some dimensions are naturally more important than others. Some dimensions will be critical to the correct functioning of the component and these are termed functional dimensions. Other dimensions will not be critical to correct functioning and these are termed non-functional dimensions. Functional dimensions are obviously the more important of the two and therefore will be more important when making decisions about the dimension value....

Engineering Drawing Car Jack

Car Jack Assembly Drawing Autocad

Obtain a component that is simple and commonly available and produce a detail drawing of it sufficient for it to be manufactured. Such a component could be a paperclip, key, drawing pin, ruler, centre punch, coat hook, glass jar, special nut or washer or bolt e.g. casellated, lock , spanner, nail, paper cup, plastic cup, CD, needle, cotton reel, cable tie, house brick, cardboard cereal box. 67. Beg, borrow or buy an artefact that consists of an assembly of parts and perform a reverse...

Datums

Engineering Symbol For Datum Point

A datum, is a point, line or surface of a component to which dimensions are referred and from which measurements are taken during inspection. The datum point or points on a component are in reality datum features since it is with respect to features that other features relate. Thus, the various features on a component are dimensioned with respect to datum features. The definition of a datum feature will be dependent upon the functional performance of a particular component. In the example shown...

Example of drawing a small hand vice

Part Drawing And Asembly Dimention

A common artefact in any workshop is a small vice. Such a small engineering vice is shown in Figure 3.1. The main body of the vice is a stubby 'U' shape in which a movable jaw is positioned between the two uprights. The movable jaw is actuated by a screw which is rotated by a small bar. Although the drawing is 'busy', the different lines help to make the artefact jump out from the page. This has been done by the use of different types of line thicknesses thick and thin and different types of...

D roughness parameters

Roughness Visual

The range of parameters calculated from a trace may be represented by the equation 'T' represents the scale of the parameter. If the trace is unfil-tered, the designation 'P' is used. After filtering, the parameters calculated are given the designation 'R' for roughness or 'W' for waviness. If parameters relate to an area, the designation 'S' is used. 'n' represents the parameter suffix which denotes the type calculated, e.g. average is 'a', RMS is 'q', Skew is 'sk', etc. 'N' refers to which of...

Lettering symbols and abbreviations

Many drawings are microfilmed and this causes a problem of legibility when drawings are blown up again to their original size. Thus, it is recommended that the distance between adjacent lines or the spacing between letters or numerals should be at least twice the line thickness. There are six ISO standards would you believe it on lettering alone they are under one standard. The six parts of ISO 3098 refer to general requirements part 0 , the Latin alphabet part 2 , the Greek alphabet part 3 ,...

Auxiliary dimensions

The standard ISO 129 1985 states 'each feature shall be dimensioned only once on a drawing'. However, there are instances when there is a need for something to be dimensioned twice for information purposes. An example is shown in Figure 4.1. The bolt is made up of three sections, the head, the bearing shaft and the screw thread. Each has a length dimension associated with it. Together these make the shaft total length. It could be convenient, during manufacture, for the machinist to know the...

Method of indicating surface finish and texture

Surface Finish Symbols

Section 6.3.1 above described parameters using lTnN However, no information was given concerning how these are added to features on a drawing. The methodology to do this is described in ISO 1302 2001. It is based on what is termed a 'tick symbol' that defines the SF and points to the surface in question via a leader line. Figure 6.13 shows the tick symbol with various descriptors surrounding it. The tick symbol is placed on the surface or an extension drawn to it. The basic tick comprises two...