Engineering drawing - Wikipedia. An engineering drawing, a type of technical drawing, is used to fully and clearly define requirements for engineered items. Engineering drawing (the activity) produces engineering drawings (the documents). More than merely the drawing of pictures, it is also a language. Engineering drawing shares some traits with artistic drawing in that both create pictures. But whereas the purpose of artistic drawing is to convey emotion or artistic sensitivity in some way (subjective impressions), the purpose of engineering drawing is to convey information (objective facts). Engineering drawing uses an extensive set of conventions to convey information very precisely, with very little ambiguity.
Relationship to other technical drawing types. Although these terms are still in use, the non- gender- specific terms draftsperson and drafter are now more common. Cascading of conventions by specialty. For example, even within metalworking, there are some process- specific conventions to be learned. Each of these trades has some details that only specialists will have memorized. Legal instruments.
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It is thus a part of a contract; the purchase order and the drawing together, as well as any ancillary documents (engineering change orders . Thus, if the resulting product is wrong, the worker or manufacturer are protected from liability as long as they have faithfully executed the instructions conveyed by the drawing. If those instructions were wrong, it is the fault of the engineer. Because manufacturing and construction are typically very expensive processes (involving large amounts of capital and payroll), the question of liability for errors has great legal implications as each party tries to blame the other and assign the wasted cost to the other's responsibility.
This is the biggest reason why the conventions of engineering drawing have evolved over the decades toward a very precise, unambiguous state. Standardization and disambiguation. Standards provide rules for their specification and interpretation. In 2. 01. 1, a new revision of ISO 8.
Invocation Principle. The implication of this is that any drawing using ISO symbols can only be interpreted to ISO GPS rules.
The only way not to invoke the ISO GPS system is to invoke a national or other standard. Now in 2. 01. 5 there is a new standardisation called BS 8. Since there are only two widely standardized definitions of size, there is only one real alternative to ISO GPS, i. ASME Y1. 4. 5 and Y1. M (most recently revised in 2. Standardization also aids internationalization, because people from different countries who speak different languages can read the same engineering drawing, and interpret it the same way.
To that end, drawings should be as free of notes and abbreviations as possible so that the meaning is conveyed graphically. Important note! The 'manufacturing' of a technical drawing however is as difficult as the actual production of the design it describes. Therefore engineers must think very clearly about what is placed on a drawing, i. Dimensioning and tolerancing principles. Ideally each party knows exactly how to read and interpret such principles, but practise shows it is not as easy.
For centuries, until the post- World War II era, all engineering drawing was done manually by using pencil and pen on paper or other substrate (e. Since the advent of computer- aided design (CAD), engineering drawing has been done more and more in the electronic medium with each passing decade.
Today most engineering drawing is done with CAD, but pencil and paper have not disappeared. Some of the tools of manual drafting include pencils, pens and their ink, straightedges, T- squares, French curves, triangles, rulers, protractors, dividers, compasses, scales, erasers, and tacks or push pins. Drafting machines are devices that aid manual drafting by combining drawing boards, straightedges, pantographs, and other tools into one integrated drawing environment.
CAD provides their virtual equivalents. Producing drawings usually involves creating an original that is then reproduced, generating multiple copies to be distributed to the shop floor, vendors, company archives, and so on. The classic reproduction methods involved blue and white appearances (whether white- on- blue or blue- on- white), which is why engineering drawings were long called, and even today are still often called, . The more generic term . In the case of CAD drawings, the original is the CAD file, and the printouts of that file are the . In recent decades another method has arisen, called model- based definition (MBD) or digital product definition (DPD).
In MBD, the information captured by the CAD software app is fed automatically into a CAM app (computer- aided manufacturing), and is translated via postprocessor into other languages such as G- code, which is executed by a CNC machine tool (computer numerical control). Thus today it is often the case that the information travels from the mind of the designer into the manufactured component without having ever been codified by an engineering drawing. In MBD, the dataset, not a drawing, is the legal instrument. However, even in the MBD era, where theoretically production could happen without any drawings or humans at all, it is still the case that drawings and humans are involved. It still takes CAD/CAM programmers, CNC setup workers, and CNC operators to do manufacturing, as well as other people such as quality assurance staff (inspectors) and logistics staff (for materials handling, shipping- and- receiving, and front office functions). These workers often use drawings in the course of their work that have been produced by rendering and plotting (printing) from the MBD dataset.
When proper procedures are being followed, a clear chain of precedence is always documented, such that when a person looks at a drawing, s/he is told by a note thereon that this drawing is not the governing instrument (because the MBD dataset is). In these cases, the drawing is still a useful document, although legally it is classified as .
Several systems of dimensioning and tolerancing have evolved. The simplest dimensioning system just specifies distances between points (such as an object's length or width, or hole center locations). Since the advent of well- developed interchangeable manufacture, these distances have been accompanied by tolerances of the plus- or- minus or min- and- max- limit types. Coordinate dimensioning involves defining all points, lines, planes, and profiles in terms of Cartesian coordinates, with a common origin. Coordinate dimensioning was the sole best option until the post- World War II era saw the development of geometric dimensioning and tolerancing (GD& T), which departs from the limitations of coordinate dimensioning (e. For example, a mass- marketed product usually requires a much higher surface quality than, say, a component that goes inside industrial machinery. Line styles and types.
Types of lines include the following: visible . They are the thickest lines on a drawing and done with a pencil softer than HB. Type B lines are dimension lines and are used for dimensioning, projecting, extending, or leaders. A harder pencil should be used, such as a 2. H pencil. Type C lines are used for breaks when the whole object is not shown. These are freehand drawn and only for short breaks.
H pencil. Type D lines are similar to Type C, except these are zigzagged and only for longer breaks. H pencil. Type E lines indicate hidden outlines of internal features of an object. These are dotted lines. H pencil. Type F lines are Type F.
H pencil. Type G lines are used for centre lines. These are dotted lines, but a long line of 1. H pencil. Type H lines are the same as type G, except that every second long line is thicker. These indicate the cutting plane of an object. H pencil. Type k lines indicate the alternate positions of an object and the line taken by that object. These are drawn with a long line of 1.
H pencil. Multiple views and projections. Types of views include the following: Orthographic projection. The origin and vector direction of the projectors (also called projection lines) differs, as explained below. In first- angle projection, the projectors originate as if radiated from a viewer's eyeballs and shoot through the 3. D object to project a 2. D image onto the plane behind it. The 3. D object is projected into 2.
D . First- angle projection is the ISO standard and is primarily used in Europe. In third- angle projection, the projectors originate as if radiated from the 3. D object itself and shoot away from the 3. D object to project a 2.
D image onto the plane in front of it. The views of the 3. D object are like the panels of a box that envelopes the object, and the panels pivot as they open up flat into the plane of the drawing. Third- angle projection is primarily used in the United States and Canada, where it is the default projection system according to ASME standard ASME Y1. M. Until the late 1. North America as well as Europe. In addition to the 6 principal views (front, back, top, bottom, right side, left side), any auxiliary views or sections may be included as serve the purposes of part definition and its communication.
View lines or section lines (lines with arrows marked . Sometimes a note tells the reader in which zone(s) of the drawing to find the view or section. Auxiliary projection.
Using the auxiliary view allows for that inclined plane (and any other significant features) to be projected in their true size and shape. The true size and shape of any feature in an engineering drawing can only be known when the Line of Sight (LOS) is perpendicular to the plane being referenced. It is shown like a three- dimensional object.
Isometric projection. Isometric projection corresponds to rotation of the object by .
One of the things that makes isometric drawings so attractive is the ease with which 6. Isometric projection is a type of axonometric projection.