Mechanical Engineering Interview Questions and Answers - GD&T

Mechanical Engineering Interview Questions and Answers - Geometric Dimensioning and Tolerancing (GD&T)

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Q001) What is the complete form of GD and T?

GD & T is the abbreviation used for Geometric Dimensioning and Tolerancing.

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Q002)  What are GD & T?

GD & T are a set of symbols.

GD & T are indicated on engineering drawings.

GD & T defines Tolerances of Form, Orientation, Location, and Run-out.

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Q003) Which GD&T standard does the industry use?

For GD&T, most industries use the ASME Y14.5 standard.

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Q004) Explain the complete form of ASME Y14.5

ASME = American Society of Mechanical Engineers

Y14.5 = Standard Number for GD&T

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Q005) Why GD&T?

GD&T is essential

*to communicate the design intent.

*to ensure the form, fit, and function of the parts/assemblies.

*to ensure interchangeability between parts/assemblies.

*to improve quality of parts/assemblies.

*lowers manufacturing costs.

*improves lead time to deliver the parts/assemblies.

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Q006) How many types of GD&T are there? What are they?

   There are five types of GD&T. They are

  1. Tolerances of FORM
  2. Tolerances of PROFILE
  3. Tolerances of ORIENTATION
  4. Tolerances of LOCATION
  5. Tolerances of RUN-OUT

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Q007) How many types of FORM Tolerances are there? What are they?

There are three types of FORM Tolerance. They are

  1. Straightness
  2. Flatness
  3. Circularity
  4. Cylindricity

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Q008) How many types of PROFILE Tolerances are there? What are they?

There are two types of PROFILE Tolerance. They are

  1. Profile of a Line
  2. Profile of a Surface

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Q009) How many types of ORIENTATION Tolerances are there? What are they?

There are three types of ORIENTATION Tolerance. They are

  1. Angularity
  2. Perpendicularity
  3. Parallelism

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Q010) How many types of LOCATION Tolerances are there? What are they?

There are three types of FORM Tolerance. They are

  1. Position
  2. Concentricity
  3. Symmetry

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Q011) How many types of RUN-OUT Tolerances are there? What are they?

There are two types of RUN-OUT Tolerance. They are

  1. Circular Run-out
  2. Total Run-out

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Q012) How many GD&T symbols are there? What are they?

There are fourteen types of GD&T symbols. They are

  1. Straightness
  2. Flatness
  3. Circularity
  4. Cylindricity
  5. Profile of a Line
  6. Profile of a Surface
  7. Angularity
  8. Perpendicularity
  9. Parallelism
  10. Position
  11. Concentricity
  12. Symmetry
  13. Circular Run-out
  14. Total Run-out

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Q013) What is Geometry?

Geometry is the study of points, lines, angles, surfaces, and solids.

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Q014) What is a Dimension?

A dimension is a measurement. For example, a rectangle has 2 dimensions, length, and height.

A circle has one dimension, either diameter or radius. A pin has 2 dimensions, the diameter of the pin and the length of the pin.

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Q015) What is a Tolerance?

Tolerance is the allowable variation in a dimension.

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Q015) Why should tolerance be provided on dimensions?

Let's take an example of a pin. The pin has 2 dimensions the diameter of the pin and the length of the pin.

The pin is manufactured by turning on a lathe. Now when the operator is machining the pin on a lathe machine, there could be human and machine errors. Due to these types of errors, it might not be practically possible to achieve the exact dimensions of the pin. Hence it is essential to provide tolerance on dimensions.

Also, note there could be errors in measuring instruments also. For example, even if the pin is manufactured for a theoretically exact dimension, it might not be able to measure that dimension exactly due to errors in measuring instruments. Hence it is essential to provide tolerance on dimensions.

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