Engineering Drawing

The engineering drawing is the most important communication tools that a company can possess. Drawings are not only technical information, but also legal documents. Their creation and maintenance are expensive and time consuming. For these reasons, the effort made in fully understanding them cannot be taken for granted.

Engineering drawing Engineering drawing is a visual language of industry and engineering 60 40 20 10 10 R5 5.5 + 0.5 0 A A 0.5 M A B C B C 11 3.7 8 + - 0.2 0.2 SECTION A-A 0.2 A

Engineering drawings require extensive thought and time to produce. Many companies are using three-dimensional (3-D) computer aided design databases to produce parts and are bypassing the traditional two-dimensional (2-D) drawings. In many ways, creating an engineering drawing is the same as a part production activity. The main difference between drawing production and part production is that the drawing serves many different functions in a company. Pricing uses it to calculate product costs. Purchasing uses it to order raw materials. Routing uses it to determine the sequence of machine tools used to produce the part. Tooling uses it to make production, inspection, and assembly fixtures. Production uses the drawing information to make the parts. Inspection uses it to verify the parts have met the specifications. Assembly uses it to make sure the parts fit as specified.

  1. Visual language of industry and engineering
  2. Relationship to artistic drawing
  3. Engineering drawing softwares
  4. Legal documents
  5. Media
  6. Model-based definition

Visual language of industry and engineering

Graphical language of industry
Graphical language of industry

An engineering drawing, is a graphical language, used to fully and clearly define requirements for engineering items.

More than just the drawing of pictures, it used to communicate ideas and information from one mind to another. Most especially, it communicates all needed information from the engineer who designed a part to the workers who will make it.

Almost all engineering drawings (except perhaps reference-only views or initial sketches) communicate not only geometry (shape and location) but also dimensions and tolerances for those characteristics.

Coordinate dimensioning was the sole best option until the post-World War II. The Need for Precise Communications developed the engineering drawings to the geometric dimensioning and tolerancing (GD&T), which departs from the limitations of coordinate dimensioning.

Drawings convey the following critical information:

  • Geometry – the shape of the object; represented as views. The basis for much engineering drawing is orthographic representation (projection).
  • Dimensions – the size of the object is captured in accepted units.
  • tolerances – the allowable variations from the nominal size for each dimension.
  • Material – represents what the item is made of.
  • Surface finish – specifies the surface quality of the item.

Relationship to artistic drawing

  • Artistic drawing convey emotion
  • Engineering drawing convey information
artistic drawing
An Artistic drawing

Engineering drawing and artistic drawing are both types of drawing, and either may be called simply "drawing" when the context is implicit. 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 requires some training to understand (like any language); but there is also a high degree of objective commonality in the interpretation (also like other languages). In fact, engineering drawing has evolved into a language that is more precise and unambiguous than natural languages. Engineering drawing uses an extensive set of conventions to convey information very precisely, with very little ambiguity. Along with these they are both drawing.

Legal documents

If the product is wrong, manufacturer is protected from liability as long as he has faithfully executed the drawing instructions.

An engineering drawing is a legal document
A legal document

An engineering drawing is a legal document (that is, a legal instrument), because it communicates all the needed information about "what is wanted" to the people who will expend resources turning the idea into a reality. It is a part of a contract. 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.


Drafting machine
Drafting machine

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.g., vellum, mylar). 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.

The English idiom "to go back to the drawing board", which is a figurative phrase meaning to rethink something altogether, was inspired by the literal act of discovering design errors during production and returning to a drawing board to revise the engineering drawing. 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, "blueprints" or "bluelines", even though those terms are anachronistic from a literal perspective, since most copies of engineering drawings today are made by more modern methods (often inkjet or laser printing) that yield black or multicolour lines on white paper. The more generic term "print" is now in common usage in the U.S. to mean any paper copy of an engineering drawing. In the case of CAD drawings, the original is the CAD file, and the printouts of that file are the "prints".

Model-based definition

For centuries, an engineering drawing was the sole method of transferring information from design into manufacture. In recent decades another method has arisen, called model-based definition (MBD). In MBD, the information captured by the CAD software app is fed automatically into a CAM app (computer-aided manufacturing), and is translated via post processor 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.

Modeling and engineering drawing softwares

  • AutoCAD by Autodesk
  • CATIA by Dassault Systemes
  • Mechanical desktop
  • Pro/ENGINEER by Parametric Technology Corporation
  • SolidWorks by SolidWorks Corp.

  • Refrences:
    • Wikipedia
    • Paul J. Drake, Jr. Dimensioning and Tolerancing Handbook