Axis GD&T Services
Common GD&T Misconceptions
Debunking Myths and Misunderstandings
Misconceptions about GD&T often lead to confusion and hesitation in its use. Myths and misunderstandings can create barriers to effective implementation, preventing teams from fully realizing its benefits. When applied correctly, GD&T can be a very powerful tool.
Myth:
GD&T Makes Parts More Expensive
Fact:
GD&T is simply a language for conveying design intent—it doesn’t require parts to be 'gold-plated.'
When correctly applied and interpreted, it actually helps reduce costs by minimizing scrap, rework, and ambiguity in manufacturing.
Myth:
Tighter Tolerances Mean Better Parts
Fact:
While tight tolerances imply quality, they may lead to unnecessary scrap and increased costs.
Overly tight tolerances are sometimes used as a shortcut to avoid proper analysis. Tolerances should be as loose as possible, but no looser.
Myth:
GD&T Depends On The Manufacturing Process
Fact:
GD&T should be based on the functional requirements of the part —not dictated by a specific manufacturing process.
As a designer, you should be aware of manufacturing techniques, but if the shop can make it with a hammer and chisel while meeting the tolerances, let them.
Myth:
Good GD&T Eliminates Non-Conformances
Fact:
Even if GD&T perfectly reflects the functional requirements and tolerances are correctly analyzed, non-conformances can still occur—because manufacturing isn't perfect.
The difference is that with proper GD&T, you can clearly determine which issues actually matter and which do not.
Where Do Tolerances Come From?
Understanding the Sources of Tolerances
One of the biggest challenges in GD&T is determining the correct tolerances for a part. Applying tolerances effectively requires a deep understanding of where they come from. Without this understanding, tolerances may be too tight, increasing costs and scrap, or too loose, leading to assembly and performance issues.
Math
Analyzing and calculating tolerance stack-ups to ensure that all components fit together correctly, maintain their intended form, and function as designed within the assembly.
Testing
When empirical data isn't available, testing tolerance variations in real-world applications can generate new data. Often, the initial tolerance is chosen arbitrarily to start.
Data Sheets
Using data sheets, such as O-ring calculators, bearing handbooks, and other sources of tested and empirical data, to determine appropriate tolerances.
Mechanical Intuition
When a feature has no constraints, a tolerance may need to be chosen arbitrarily. This should be done sparingly, and be well-documented for easy reference and future adjustments.
What Makes A Great Drawing?
Key Elements of Clear and Effective Drawings
A great engineering drawing clearly conveys design intent without ambiguity. It gives everyone involved in the manufacturing process the best chance of correctly interpreting the requirements, reducing non-conformances and costly rework.
Proper Datums
Datums should be selected based on function and assembly needs. A well-planned datum structure improves inspection effectiveness, and ensures proper fit and function.
Proper Tolerances
Tolerances should be as loose as possible, but no looser. This minimizes the number of parts scrapped, and maintains reliable assembly performance.
Proper Feature Control
Applying geometeric controls based on functional requirements minimizes ambiguity, and ensures parts meet the design intent.
Clear Layout
Well-organized drawings are easier to interpret. If spacing out views to prevent clutter means adding more pages, do so. Why make an ugly drawing when it could be beautiful?