Engineering drawing

An engineering drawing is a type of technical drawing used to share clear information about an object. It helps people understand how something should be built or made. One common use is to show the exact shape and size needed to create a part, which is called a detail drawing. Usually, many drawings are needed to fully describe even a simple part. These drawings are connected by a "master drawing," known as an assembly drawing. This main drawing lists the numbers of the smaller parts, how many of each are needed, what they are made from, and sometimes even 3D pictures to help locate each piece.

Engineering drawings often include several different views of a part, like front, side, and top views, to give a complete picture. They use special abbreviations and symbols to save space and may also have extra text to explain important details. Only the necessary information is included, such as the exact dimensions of the part. These dimensions are usually written just once to avoid mistakes. The drawings also show tolerances, which are small allowed differences in size, so the part can be made and still work correctly. Sometimes, more detailed production drawings are made from these engineering drawings to guide the actual building of the part. Every drawing has a special box called a title block that tells who made the drawing, who checked it, what units were used, what the different views mean, the name of the drawing, and its number.

History

Technical drawing has been a part of human history for thousands of years, helping people share ideas about big structures like temples and pyramids. Ancient groups like the Egyptians and Mesopotamians used simple drawings to plan their buildings and irrigation systems. Later, in ancient Greece and ancient Rome, engineers used drawings to show how to build things like bridges and aqueducts.

During the Renaissance, artists and inventors began using more advanced drawing methods. The Industrial Revolution brought even more changes, with new rules and ways to make drawings clearer and more exact. Tools like T-squares and protractors helped create precise plans for big projects such as trains and skyscrapers. Today, computers and computer-aided design (CAD) software make drawing faster and easier, but the basic ideas from the past are still important.

Standardization and disambiguation

Engineering drawings can be complex, so standards help make sure everyone understands them the same way. These rules help people from different countries, even if they speak different languages, read and interpret drawings correctly.

One important set of standards is ASME Y14.5, used widely in the United States. Another key standard is ISO 8015 (Geometrical product specifications (GPS) — Fundamentals — Concepts, principles and rules), which is important worldwide. These standards make sure that engineering drawings are clear and consistent for everyone to use.

Media

For many years, engineering drawings were made by hand using tools like pencils, pens, and rulers on paper. This changed with the introduction of computer-aided design (CAD), which is now used for most engineering drawings. Even though CAD is common today, some people still use pencil and paper.

Hand tools for drawing include pencils, pens, straightedges, T-squares, and rulers. There are also special tools like French curves, protractors, and dividers. In the past, people used slide rules for calculations, but now calculators are used instead. The phrase "go back to the drawing board" comes from the practice of revisiting drawings to fix problems. Today, most engineering drawings are made with CAD, but copies are still often called "blueprints" even though they are usually printed in black ink.

Systems of dimensioning and tolerancing

Engineering drawings show not just the shape of an object but also its sizes and how much those sizes can vary. There are different ways to write down these sizes and variations. The simplest way is to write down distances between points, like how long or wide something is. Over time, these distances came with rules about how much they could change.

One method, called coordinate dimensioning, uses points and lines to describe an object using a starting point, like on a map. Another method, called geometric dimensioning and tolerancing, helps describe shapes and sizes more flexibly.

Common features

Drawings tell us important information about an object. They show the shape of the object from different angles, like front, top, and side views. They also give us the size of the object using units, and tell us what the object is made of and how smooth its surface should be.

There are different types of lines used in drawings. Some lines show edges we can see, while others show hidden edges or special features like circles. Each type of line has a different style, like solid lines or dashed lines, to make it easy to understand what the drawing is showing.

Conventional parts (areas)

Every engineering drawing has a special area called a title block. This block contains important information such as the drawing’s title, number, and the name of the company that made it. It also includes details like the measurement units and any legal notices about the drawing.

Other important parts of a drawing include a revisions block, which lists changes made to the drawing, and a notes list that gives extra instructions. The main area of the drawing, called the field, shows the actual design. Sometimes, there is also a list of materials or parts used, which can be found near the title block or in a separate document.

Abbreviations and symbols

Engineering drawings use many abbreviations and symbols to make designs easier to understand. For example, cold rolled steel is often called CRS, and diameter might be written as DIA, D, or ⌀. These drawings work well in any language because most words are only in the title block, and symbols are used instead of words elsewhere.

With computers now making many drawings, some older symbols are not used as much. This can make it tricky to read very old hand-drawn plans, especially from times like World War II, because the meanings of some symbols are hard to find today.

Example

This is an example of an engineering drawing. It shows different line types, each with its own color to make things clear.

• Black lines show the object and its texture.
• Red lines show hidden parts.
• Blue lines show the center of a piece or opening.
• Magenta lines show phantom lines or cutting planes.

Sectional views are shown by arrows pointing in the direction of the view.

Legal instruments

An engineering drawing is like a legal document because it tells people exactly what they need to build or make. When combined with a purchase order and other papers, the drawing becomes part of a contract. If something goes wrong with the final product, the worker or manufacturer is protected if they followed the drawing correctly. If the drawing itself has mistakes, then the engineer is responsible. This matters a lot because making things often costs a lot of money.

Relationship to model-based definition (MBD/DPD)

For a long time, engineering drawings were the main way to share design details for making products. Recently, a new method called model-based definition (MBD) or digital product definition (DPD) has become popular. In MBD, design information is entered into special computer programs and directly used to create products, sometimes without needing a traditional drawing.

Even with MBD, people still use drawings to help with making and checking products. These drawings come from the design data and are marked as reference only, meaning the main design information comes from the computer data, not the drawing.