China
Africa
Explore chapters and articles related to this topic
Two-Dimensional Engineering Drawings
Published in Ali Jamnia, Introduction to Product Design and Development for Engineers, 2018
Merriam-Webster's online dictionary definition of the word datum is: “something used as a basis for calculating or measuring.” In the context of engineering drawings, a datum is a reference point, line, or surface. Theoretically, a datum is a perfect geometric (not physical) shape; that is, a point, line, or plane. The reason datums are important is they enable the design engineer to align and assemble variouscomponents together. By providing a sequence of datums and how various features of components relate to these datums, the design engineer conveys to manufacturing what the design intends and how the parts would assemble once fabricated. On the basis of this knowledge of parts assembly, incoming quality inspection may take place to release parts for assembly. Developing accurate datums across engineering drawings is the cornerstone of interchangeability.
Engineered products
Published in Mike Tooley, Engineering GCSE, 2012
Polar coordinates consist of one linear distance and an angle as shown in Figure 2.36(b). Dimensioning in this way is useful when the work is to be machined on a rotary table. It is widely used when setting out hole centres round a pitch circle. Quite frequently both systems are used at the same time as shown in Figure 2.36(c). During our discussion on marking out, we have kept referring to datum points, datum lines and datum edges. A datum is any point, line or surface that can be used as a basis for measurement. When you go for a medical check-up, your height is measured from the floor on which you are standing. In this example the floor is the basis of measurement, it is the datum surface from which your height is measured.
Blueprint Reading
Published in Frank R. Spellman, The Science of Wind Power, 2022
A datum (a point, axis, or plane) identifies the origin of a dimensional relationship between a particular (designated) point or surface and a measurement; that is, it is assumed to be exact for the purpose of reference and is the origin from which the location or geometric characteristic of features or a part are established. The datum is indicated by the assigned letter preceded and followed by a dash, enclosed in a small rectangle or box (see Figure 6.46).
NOAA’s national water level observation network (NWLON)
Published in Journal of Operational Oceanography, 2019
Vertical datums are important pieces of information needed when working with tidally influenced ecosystems. A datum is a base elevation used as a reference from which to reckon heights or depths. A tidal datum is a standard elevation defined by a certain phase of the tide and is used as a reference to measure local water levels. Tidal datum information supports inundation analysis (frequency and duration) for tidally influenced habitats, as accurate estimates of local inundation regimes contribute to the successful restoration of degraded wetlands. Inundation analyses above a specified elevation threshold are also available using observed and historical data from NWLON stations, which is important for analyzing return frequencies for coastal flooding. In addition, CO-OPS also provides annual and monthly exceedance probability levels for select CO-OPS water level stations with at least 30 years of data. When used in conjunction with real-time station data, exceedance probability levels can be used to evaluate current conditions and determine whether a rare inundation event is occurring.
Reconstructing original design: Process planning for reverse engineering
Published in IISE Transactions, 2023
Zhaohui Geng, Arman Sabbaghi, Bopaya Bidanda
Partial Procrustes Analysis (PPA) was developed by the SSA community to register Xis from the configuration space to size-and-shape space (Dryden and Mardia, 2016). However, parts are produced and inspected by fixing the defined datum features in traditional manufacturing, especially machining processes (Pandya et al., 2002). The datum features define a reference system for machining or metrology by restricting the degrees of freedom, which plays a critical role in drawing, tolerancing, and measuring. Therefore, it is reasonable to register the whole landmarks by aligning the datum for near-real practice solutions. Identifying the datum features is part-dependent and requires design and engineering knowledge, which is omitted here.
Tolerance estimation and metrology for reverse engineering based remanufacturing systems
Published in International Journal of Production Research, 2022
Since each of the datums establishes and fixes 3 degrees of freedom, a datum reference frame is required to remove all 6 degrees of freedom for manufacturing and inspection purposes, including translations in the -, -, and -directions and rotations around them. One possible practice is to define three planar datum features to establish the datum reference frame. Similar to the candidate datum set, the candidate datum reference frame set can be established, within which the actual datum reference frame can be determined by the minimax or maximin condition for a specific tolerance type. The three planar datum features are ranked as primary, secondary, and tertiary datum features, respectively. The secondary datum is constrained to be perpendicular to the primary one, while the tertiary datum is defined to be orthogonal to both the primary and secondary datums. Therefore, within tolerance estimation study, the candidate datum reference frame set can be found by finding the primary candidate datum set. For each primary datum candidate, the corresponding datum reference frame candidate is unique, since the secondary and tertiary datums are restricted by the mutual orthogonal conditions and the points supporting constraints defined for datums. Specifically, the algorithm for the datum reference frame is as follow: Apply the QuickHull algorithm to find the convex hull of the points corresponding to the predetermined primary datum feature;Find the subset of the facets of the convex hull, , within which the whole point cloud is on one side of the facet;For each component, , of : Find the plane with respect to the predetermined secondary datum feature, which is perpendicular to ;Find the plane with respect to the predetermined tertiary datum feature, which is perpendicular to and ;Append to the set .