What is GD&T & Why is it so critical in Mechanical Design of Products?

➲ GD&T is the functional dimensioning & tolerancing of the part in order to ensure that part performs intended function in the assembly.

➲ The purpose of this blog is to educate aspiring mechanical design engineers about the importance of GD&T knowledge in overall product design of functional concepts.




Geometric Dimensioning & Tolerancing (GD&T):

➲ GD&T consists of definitions, rules, symbols & conventions in order to define size, form, orientation, location & profile of the features to meet the functional requirements of the part.

➲ ASME Y14.5-2018 & ISO1101 are the most popular GD&T standards widely used by global industries.

➲ Form symbols controls straightness, flatness, circularity & cylindricity of the features whereas Orientation symbols control perpendicularity, angularity or parallelism of features or Feature of sizes w.r.t. Datums.

➲ Runout Controls axis shift & surface irregularities w.r.t. datum axis. We can control circular runout or total runout around datum axis.

➲ Location controls position of features w.r.t. other features as well as datum features. They also control symmetry as well as concentricity of multiple Feature of sizes.

➲ Profile symbols control size, form, orientation & location based upon feature control frame.

➲ Modifying symbols or Modifiers on other hand provide additional meaning to the GD&T controls and they could be applied inside or outside Feature Control Frame based upon type of modifiers.


Learn more about GD&T: https://youtu.be/kLEgkbaV0OA?si=gpBJ9RVPHhNUlVSI


GD&T has some definite advantages over coordinate system:

  1. GD&T allows us to provide circular tolerance zone as against square | rectangular tolerance zone in coordinate system which provides 57% more tolerance area which means more functional parts rejected earlier, now will be acceptable.
  2. Unlike coordinate tolerance system, GD&T allows us to apply geometric control values at Maximum or Least Material conditions which means based upon actually produced size of Feature, we can get additional tolerance (Bonus) to control orientation and location which might save manufacturing & inspection cost for the company.
  3. GD&T removes ambiguity in manufacturing & inspection by providing clearly defines datums and their sequence of constraining the part for inspection.


GD&T also has limitations:

  1. Skill requirement would be higher
  2. Initial investments in measurement instruments is higher
  3. Cost of hiring resources is higher


➲ GD&T is must to have skill for design engineers because lack of this skill might result into substandard drawings and eventually substandard parts which may not meet functional needs.

➲ Design Engineers must learn GD&T a per ASME or ISO standard, gain confidence to select right geometric control and value to deliver functionally working part.


Read my other blogs to understand top mechanical design skills for 10X career growth.

Read blog: https://designgekz.com/most-in-demand-skills-in-mechanical-design-engineering/


⏩ For career planning or enquiring about the courses, write to us at kevinkutto@designgekz.com or call us @ +91-8329029492 | 9881521371


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