Datums
Datums are reference points or surfaces used in engineering and technology to establish a common point of origin for measurements and alignments. They provide a consistent framework for designing and manufacturing components, ensuring accuracy and compatibility in assembly and production processes. Datums are essential for maintaining precision and standardization in various industries, including manufacturing, automotive, and aerospace.
5 Key excerpts on "Datums"
eBook - ePub- Prof. Sham Tickoo(Author)
- 2017(Publication Date)
- CADCIM Technologies(Publisher)
...Chapter 5 Datums Learning Objectives After completing this chapter, you will be able to: • Understand the need of Datums in modelling • Work with three default datum planes • Understand selection methods in Creo Parametric • Create datum planes using different constraints • Create datum axes using different constraints • Create datum points • Create datum coordinate system • Create datum curves • Understand asynchronous datum features Datums Datums are references used to describe the position of a feature(s). They act as reference for sketching a feature, orienting a model, assembling components, and so on. Datums are imaginary features with no mass or volume. Remember that Datums play a very important role in creating complex models in Creo Parametric; therefore, you must have a good understanding of Datums. Datums are considered to be features but not model geometry. In Creo Parametric, Datums exist as datum plane, datum curve, datum point, datum coordinate system, datum graph, and so on. Need for Datums in modeling Generally, most of the engineering components or designs consist of more than one feature. First the base feature of the model is created and then other features of the model are added. Since all features of a model cannot be drawn on a single plane, therefore, to draw rest of the features, sometimes, additional planes have to be created or selected. Also, most of the times, the three default datum planes are not enough to create a complex model having many features. For example, Figure 5-1 shows a simple model that consists of two features that require two different planes. In Figure 5-1, any one of the two features defined on two different planes can be considered as the base feature. However, in this discussion, the feature that is selected as the base feature is shown in Figure 5-2. After creating the base feature, the next feature will be created. For the next feature, a sketching plane has to be defined...
eBook - ePubManual of Engineering Drawing
Technical Product Specification and Documentation to British and International Standards
- Colin H. Simmons, Dennis E. Maguire(Authors)
- 2012(Publication Date)
- Butterworth-Heinemann(Publisher)
...Chapter 22 Geometrical Tolerancing and Datums Geometrical Tolerances The object of this section is to illustrate and interpret in simple terms the advantages of calling for geometrical tolerances on engineering drawings, and also to show that, when correctly used, they ensure that communications between the drawing office and the workshop are complete and incapable of misinterpretation, regardless of any language barrier. Applications Geometrical tolerances are applied over and above normal dimensional tolerances when it is necessary to control more precisely the form or shape of some feature of a manufactured part, because of the particular duty that the part has to perform. In the past, the desired qualities would have been obtained by adding to drawings such expressions as ‘surfaces to be true with one another’, ‘surfaces to be square with one another’, ‘surfaces to be flat and parallel’, etc., and leaving it to workshop tradition to provide a satisfactory interpretation of the requirements. 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 incorporates these symbols. Caution – It must be emphasized that geometrical tolerances should be applied only when real advantages result, when normal methods of dimensioning are considered inadequate to ensure that the design function is kept, especially where repeatability must be guaranteed. Indiscriminate use of geometrical tolerances could increase costs in manufacture and inspection...
eBook - ePub- Roger Timings(Author)
- 2007(Publication Date)
- Routledge(Publisher)
...This is a single line from which or along which dimensions are taken when measuring and marking out. It is frequently the centre line of a symmetrical component. • Edge datum. This is also known as a service edge. It is a physical surface from which dimensions can be taken. This is the most widely used datum for marking out. Usually two edges are prepared at right angles to each other. They are also referred to as mutually perpendicular datum edges. These two edges ensure that the distances marked out from them are also at right angles to each other. • Surface datum. For example, this can be the working surface of a surface plate or a marking-out table. It provides a common datum to support the work and the measuring and marking-out equipment in the same plane. For example, if you set your work with its datum edge on the surface datum of the marking-out table, and you set your surface gauge or scribing block to 25 mm, then the line you scribe on your work will be 25 mm from its datum edge. This is because the datum surface of the foot of the surface gauge and the datum surface of your work are both being supported in the same plane by the surface plate or marking-out table, as shown in Fig. 7.16. Figure 7.16 Marking out from a datum surface 7.5.1 Co-ordinates The distance from a datum to some feature such as the centre of a hole is called an ordinate. In practice, two such dimensions are required to fix the position of a feature on a flat surface. These two ordinates are called co-ordinates. There are two systems of co-ordinates in common use. 7.5.2 Rectangular co-ordinates The feature is positioned by a pair of ordinates (co-ordinates) lying at right angles to each other and at right angles to the two axes or datum edges from which they are measured...
eBook - ePubManual of Engineering Drawing
Technical Product Specification and Documentation to British and International Standards
- Colin H. Simmons, Dennis E. Maguire(Authors)
- 2009(Publication Date)
- Butterworth-Heinemann(Publisher)
...Chapter 20. Geometrical tolerancing and Datums Geometrical tolerances The object of this section is to illustrate and interpret in simple terms the advantages of calling for geometrical tolerances on engineering drawings, and also to show that, when correctly used, they ensure that communications between the drawing office and the workshop are complete and incapable of misinterpretation, regardless of any language barrier. Applications Geometrical tolerances are applied over and above normal dimensional tolerances when it is necessary to control more precisely the form or shape of some feature of a manufactured part, because of the particular duty that the part has to perform. In the past, the desired qualities would have been obtained by adding to drawings such expressions as ‘surfaces to be true with one another’, ‘surfaces to be square with one another’, ‘surfaces to be flat and parallel’, etc., and leaving it to workshop tradition to provide a satisfactory interpretation of the requirements. 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 incorporates these symbols. Caution – It must be emphasized that geometrical tolerances should be applied only when real advantages result, when normal methods of dimensioning are considered inadequate to ensure that the design function is kept, especially where repeatability must be guaranteed...
eBook - ePubManual of Engineering Drawing
British and International Standards
- Colin H. Simmons, Dennis E. Maguire, Neil Phelps(Authors)
- 2020(Publication Date)
- Butterworth-Heinemann(Publisher)
...22 Geometrical tolerancing and Datums Abstract This chapter covers the basic requirements of ISO1101 and ISO5459 giving in simple terms the advantages of applying geometrical tolerances and Datums on engineering drawings, and to show that, when correctly used, they ensure that communications between the design office and the workshop are complete and incapable of misinterpretation, regardless of any language barrier. Firstly, this chapter identifies and explains the symbology used, the method of indicating and applying tolerance frames and tolerance frames. Secondly this chapter covers Datums giving examples of how Datums, Datum Systems, Datum Targets and Common Datums are constructed and indicated. Finally, an example of dimensioning and tolerancing of Non-Rigid Parts is illustrated. Keywords Geometrical; Tolerance; Datums; Theoretically Exact; Non-rigid Geometrical tolerances The object of this section is to illustrate and interpret in simple terms the advantages of applying geometrical tolerances on engineering drawings, and also to show that, when correctly used, they ensure that communications between the design office and the workshop are complete and incapable of misinterpretation, regardless of any language barrier. In this chapter and Chapter 23, the basic rules are presented, readers are recommended to study ISO1101 and ISO5459 for a complete understanding. Applications Geometrical tolerances are applied over and above normal dimensional tolerances when it is necessary to control more precisely the form or shape of some feature of a manufactured part, because of the particular duty that the part has to perform...
