Learning GD&T? Check out these Best Practices from our Engineers

GD&T, or Geometric Dimensioning and Tolerancing, serves as a symbolic language crucial for defining and conveying engineering tolerances. This systematic approach not only communicates design intent effectively but also aids engineers and manufacturers in precisely managing variations within manufacturing processes.

From material selection to supplier communication, there’s a lot that OEMs and component manufacturers need to get right to successfully launch a product. Countless problems threaten to derail timelines or add unforeseen costs, particularly during that transition from design and development to full-scale production.

When it's time to bridge the gap between the design and production phases, your costs, quality, supply chain, and production hinge on the communication between engineers and machinists. And the work you do in the early days of design will determine your product's ability to meet specifications and quality standards in the production phase, as well as initial and lifetime costs.

GD&T is an important piece of that engineering-manufacturing communication. It provides a common language for engineers and manufacturers to ensure that parts and assemblies are produced correctly, consistently, and affordably.

10 GD&T Best Practices to Use on Part Drawings

When it comes to part drawings and working with your machining supplier, implementing GD&T best practices is crucial for ensuring accurate manufacturing and assembly processes. 

There are many ways you can use GD&T to improve part drawings and convey design intent, but our engineering team recommends the following best practices: 

1. Datum structures should be physical, functional features - e.g., bores, faces, bosses
2. Use basic tolerancing correctly – remember that basic dimensions are theoretically perfect and have no tolerance; they’re used to locate your datums
3. Don't over-tolerance – use Least and Max Material Conditions to relieve some tolerances and avoid scrapping parts unnecessarily
4. Avoid ambiguous callouts when possible – e.g., theoretical/virtual points, multiple interpretations
5. Use the most efficient tolerance for the feature you’re tolerancing – e.g., using profiles to define a surface rather than a true position
6. Qualify your datums – e.g., provide form and relational callouts back to each other
7. Use composite callouts where necessary – e.g., composite positions for hole patterns
8. Become familiar with commonly used characteristics – e.g., profile, runout, position
9. Understand datum structure – 3 mutually orthogonal features
10. Call out tolerances that have a lower range than General Tolerances on your drawing

By following these GD&T best practices, you can ensure that their part drawings are accurately translated into finished products and that the CNC machining process yields parts that meet the required specifications.

Benefits of Working GD&T Knowledge

With a working knowledge of GD&T, engineers and machinists can communicate design intent with little to no confusion, accurately define tolerances, understand the impact of dimensional variations, and identify potential manufacturing issues early in the design phase.

Because GD&T allows you to specify tolerances more precisely, you can ensure that parts and assemblies meet design requirements and perform their intended functions. This leads to improved product quality and reliability. By understanding the impact of dimensional variations and tolerances, you can optimize designs for manufacturability, identify manufacturing issues early in the design phase, and reduce production costs and time-to-market.

In addition to following these best practices with your part drawings, a deeper, working knowledge of GD&T will profoundly improve collaboration and a product's quality beyond the design phase.