GD&T is important because it ensures that mating parts fit together well and the universal language works regardless of who you are working with.
Understanding tolerance is an important part of GD&T training. A tolerance is an acceptable amount of dimensional variation that will still allow an object to function correctly.
According to ANSI and ASME Standard Y14.5,each dimension shall have a tolerance, except those dimensions specifically identified as reference, maximum, minimum or stock. The tolerance may be applied directly to the dimension or indicated by a general note located in the title block of the drawing.
There are three basic tolerances that occur most often on working drawings:
- Limit Dimensions – These are two dimensional values stacked on top of each other. The dimensions show the largest and smallest values allowed. Anything in between these values is acceptable. These are limit dimensions because the upper and lower dimensional sizes are stacked on top of each other.
- Unilateral – Aunilateral tolerance exists when a target dimension is given along with a tolerance that allows variation to occur in only one direction. This tolerance is unilateral,because the size may only deviate in one direction.
- Bilateral Tolerances – Abilateral tolerance exists if the variation from a target dimension is shown occurring in both the positive and negative directions.
If no tolerances are specified at the dimension level, then general tolerances may be applied by deliberately controlling the number of values past the decimal point on each dimension.
For total tolerance, a measuring device should be able to accurately measure within 1/10th of the total blueprint tolerance identified.
Want to learn more? Tonex offers Geometric Dimensioning and Tolerancing Training Workshop, a 2-day course that covers the key concept of Geometric Dimensioning and Tolerancing.
Tonex also offers two other courses in Lean Manufacturing. These courses are:
For more information, questions, comments, contact us.