How to Read Mechanical Drawings

What if you were working in another country and you received instructions for fabricating a ship or airplane in a foreign language? That might make your job difficult. Thankfully, mechanical drawings is a universal language that all welders can understand. Knowing how to read them can allow you to ply your trade anywhere in the world. ¹ Here is an introduction to what you will need to understand about mechanical drawings.

What Is Mechanical Drawing?

You may already be familiar with blueprints from welding class. They’re types of mechanical drawings. ² Both use symbols to create metal fabrications that welders can read and understand regardless of what language they speak or measuring system they use. ³

How Do You Read Mechanical Drawings?

Use the following three tips to help you read mechanical drawings.

1. Understand the Scope of the Project

Your first step when you receive a set of drawings is to review all of the essential information about the project:

• Specifications: details about the types and grades of materials to be used.
• Project Routing Information: indicates where the part goes next in the assembly line.
• Bill of Materials: a list of the items needed to build the weld.

2. Learn the “Alphabet of Lines”

Mechanical drawings has its own alphabet. Each line represents a part of the illustrated object. This group of lines are known as the “Alphabet of Lines” and every welder should learn them. ⁴ Here are just a few of the lines you will learn in welding training .

• Object lines:  Solid lines that show the edges and outlines of an object and where they intersect.
• Hidden Lines: Dashes that indicate edges, corners, and curved surfaces that are hidden behind the surface of the object.
• Centerlines: Indicate and bisects the center point of an object.
• Extension Lines: Thick, solid, parallel lines that extend out from an object.
• Dimension Lines: Show the measurement of an object.
• Cutting Plane Lines: Imaginary cut that shows a sectioned off internal part of an object that is not viewable from the outside.
• Break Lines: Look similar to graph lines and show if a part of an object was removed.
• Leaders and Arrows: Comprising a solid line with a point at the end identify parts, locations and are the basis of welding symbols.
• Phantom Lines: Series of dashes alternate position of moving parts or as a place holder for one to be added later. ⁵

Why Do Welders Need Mechanical Drawing?

Nearly every fabricated product starts with a mechanical drawing. Whether you’re making a product or inspecting another welder’s work, understanding how to read the instructions in the drawing is an essential part of your job. Without this ability, it would be nearly impossible to do complete any fabrication.

1 – Welding Principles and Applications; Author: Larry Jeffus; Delmar Cengage Learning; Seventh Edition; Textbook page 482
2 – http://www.merriam-webster.com/dictionary/blueprint
3 – https://www.reference.com/art-literature/mechanical-drawing-blueprint-reading-related-be7a713c33e823dc
4 – https://www.reference.com/education/meaning-alphabet-lines-59482575180d2a44
5 – https///www.youtube.com/watch?v=1Hm5Zyjmjac