HOW TO READ ENGINEERING DRAWING - GD&T SYMBOLS IN DETAIL

HOW TO READ ENGINEERING DRAWING IN EASY WAY 

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Engineering drawing is a critical communication tool that plays a vital role in the design and manufacturing of products. It is a graphical representation of a component, assembly, or system that contains all the necessary information needed to create, test, and manufacture a product. In this blog, we will discuss how to read and understand engineering drawings.

Engineering drawing is a graphical representation of an object or structure, which is used to communicate design and manufacturing details. It is a language of its own, with various types of lines and symbols used to convey specific information. Here are the types of lines used in engineering drawing along with their details:

1. Visible Lines: Visible lines are thick continuous lines that are used to show the outline and shape of an object. These lines are drawn with a dark pencil or ink and are the most common type of line in engineering drawing.

2. Hidden Lines: Hidden lines are thin dashed lines used to show features that cannot be seen in the current view. They are typically used to show the inside of an object or to clarify the shape of an object.

3. Center Lines: Center lines are thin lines made up of alternating long and short dashes. They are used to indicate the center of a cylindrical object or the axis of a symmetrical object. Center lines are also used to indicate the location of holes or other features that are symmetrical about an axis.

4. Dimension Lines: Dimension lines are thin continuous lines with arrows at each end. They are used to indicate the size of an object or feature. The dimension value is usually written in between the arrows or outside the drawing.

5. Extension Lines: Extension lines are thin continuous lines used to indicate the extent of the dimension line. They are typically drawn perpendicular to the dimension line and extend past the object or feature being dimensioned.

6. Section Lines: Section lines are thin lines used to indicate where an object has been cut in a section view. They are typically drawn at a 45-degree angle and spaced evenly apart.

7. Leader Lines: Leader lines are thin continuous lines with an arrow or dot at one end and a note or label at the other end. They are used to point to a specific feature or location on the drawing and are typically used in conjunction with a note or label.

8. Break Lines: Break lines are thin jagged lines used to indicate a break in an object. They are typically used to save space on the drawing or to show a feature that would otherwise be too large to fit on the drawing.

These are the most commonly used types of lines in engineering drawing. It is important to understand the purpose of each line and how to use them correctly to create accurate and clear drawings.

Understanding Dimensioning

Another critical aspect of engineering drawing is dimensioning. It refers to the process of adding measurements to the drawing. The dimensions provide critical information about the size, shape, and tolerance of the component, assembly, or system. The following are the common methods used for dimensioning:

1. Aligned Dimensioning: This method involves placing the dimensions parallel or perpendicular to the object being dimensioned.

2. Unidirectional Dimensioning: This method involves placing the dimensions in a single direction, typically left to right or bottom to top.

3. Chain Dimensioning: Chain dimensioning is used when a series of features are dimensioned in sequence using a single dimension line.

Understanding Geometric Tolerancing

Geometric tolerancing is a way of specifying allowable variation in geometric form and location of features. It is used to communicate the required level of precision or accuracy of a component, assembly, or system. Geometric tolerances are expressed using symbols, and each symbol has a specific meaning. The following are some of the most common geometric tolerancing symbols:

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GD&T (Geometric Dimensioning and Tolerancing) is a symbolic language used in engineering drawings to communicate design and manufacturing requirements. It includes a set of symbols, text, and tolerances that provide precise information about the size, shape, and orientation of parts and assemblies. The following are the most common GD&T symbols used in engineering drawings:

1. Flatness: The flatness symbol is represented by a straight line with a circle at the end. It is used to indicate how flat a surface should be, within a specified tolerance zone.
2. Straightness: The straightness symbol is represented by a straight line with an arrow at each end. It is used to indicate how straight a feature should be, within a specified tolerance zone.
3. Circularity: The circularity symbol is represented by a curved line with an arrow at each end. It is used to indicate how circular a feature should be, within a specified tolerance zone.
4. Cylindricity: The cylindricity symbol is represented by a circular shape with a straight line across the middle. It is used to indicate how cylindrical a feature should be, within a specified tolerance zone.
5. Profile of a surface: The profile of a surface symbol is represented by two parallel lines with an arc on top. It is used to indicate how closely a surface should match the specified profile, within a specified tolerance zone.
6. Profile of a line: The profile of a line symbol is represented by two parallel lines with an angle at each end. It is used to indicate how closely a line should match the specified profile, within a specified tolerance zone.
7. Angularity: The angularity symbol is represented by a straight line with an angle at each end. It is used to indicate how straight or angled a feature should be, within a specified tolerance zone.
8. Parallelism: The parallelism symbol is represented by two parallel lines with arrows pointing in the same direction. It is used to indicate how parallel two surfaces or features should be, within a specified tolerance zone.
9. Perpendicularity: The perpendicularity symbol is represented by a straight line with a horizontal line at the end. It is used to indicate how perpendicular a surface or feature should be, within a specified tolerance zone.
10. Position: The position symbol is represented by a circle with a crosshair in the middle. It is used to indicate how precisely a feature or axis should be located, within a specified tolerance zone.
11. Concentricity: The concentricity symbol is represented by two circles, one inside the other, with a horizontal line through the middle. It is used to indicate how centered a feature or axis should be, within a specified tolerance zone.
12. Runout: The runout symbol is represented by a circular shape with an arrow at each end. It is used to indicate how much a feature or surface can deviate from a true shape or center, within a specified tolerance zone.

By understanding and correctly applying these GD&T symbols, engineers and manufacturers can communicate design and manufacturing requirements with precision and accuracy, reducing errors and improving efficiency in the production process.

In engineering, a fit refers to the relationship between two mating parts in an assembly. There are three types of fits: clearance fit, interference fit, and transition fit. Each type of fit is defined by the amount of interference or clearance between the two mating parts.

1. Clearance Fit: A clearance fit is one where the two mating parts are designed to have a small amount of space between them. In this type of fit, the maximum diameter of the shaft is less than the minimum diameter of the hole. This creates a gap or clearance between the two parts, which allows for easy assembly and disassembly of the parts. Clearance fits are used when a loose fit is desired, such as in the case of a bearing and its housing.
2. Interference Fit: An interference fit is one where the two mating parts are designed to have a slight interference or overlap between them. In this type of fit, the maximum diameter of the shaft is greater than the minimum diameter of the hole. This creates a small amount of pressure or friction between the two parts, which results in a secure and stable connection. Interference fits are used when a tight fit is desired, such as in the case of a gear and its shaft.
3. Transition Fit: A transition fit is one where the two mating parts have both clearance and interference. In this type of fit, the maximum diameter of the shaft is slightly less than the minimum diameter of the hole, creating a clearance at some points and interference at others. This type of fit provides a balance between the advantages of clearance and interference fits. Transition fits are used when both tight and loose fits are needed, such as in the case of a piston and its cylinder.

These three types of fits are important considerations in engineering design, as the fit between mating parts can greatly affect the performance and durability of the assembly. It is essential to choose the appropriate type of fit based on the specific application and requirements of the assembly.