Communicating in microns: the importance of geometric dimensioning and tolerancing

Communicating in microns: the importance of geometric dimensioning and tolerancing

Precision engineering pays big dividends in manufacturing. There’s very little room for error in building a next-generation electric vehicle. And even less room for error in the micron-precise computer chips to control that vehicle. When safety’s at stake, even the smallest mistakes can have massive legal and financial impacts.

When a car manufacturer like Tesla spends billions to build their newest European Gigafactory, precision is a must. Each of the 500,000 vehicles produced each year must meet a precise standard. The way a manufacturer achieves this precision comes down to a set of symbols. 

These symbols are the language of geometric dimensioning and tolerancing (GD&T). GD&T will undoubtedly play a part in turning design into reality in the Tesla factory’s tooling and production lines. The same language is spoken globally by engineers and designers, from the context of European car manufacturing or in Australia’s quality-driven engineering environment.

A global language of precision
Since its introduction in the 1940s, the concept and practice of GD&T has become the industry standard. The American Society for Mechanical Engineers (ASME) sponsors the development of the Y14 series of drawing standards. The International Organization for Standardization (ISO) also publishes drawing standards. GD&T standards from both groups are used in Australia.
The new ASME Y14.5 2018 standard updates GD&T’s symbolic language, refining variations in some tolerancing and dimensioning scenarios. It also succinctly defines the language to better communicate design intent.
If you’re creating or interpreting engineering drawings for manufacturing, understanding and applying the updated 2018 ASME Y14.5 standard is crucial.
The impact of misinterpreting GD&T
GD&T can help communication in a team that designs and manufactures any component. GD&T annotation takes the place of pages of written data to describe feature acceptance zones, as related to a specific reference frame. This allows anyone who reads the GD&T language correctly to understand what’s needed for the component to function or fit properly.

GD&T is an essential tool, but it’s also a complex language with its own logic, syntax and grammar. Misinterpretation and mistakes can lead to a major loss of productivity. This could range from rework and confusion, right through to lawsuits for damages or death resulting from a failed component.
Small changes make a big difference
GD&T expert Dr Patrick J. McCuistion has had a long career in furthering GD&T knowledge and standards. Based in the USA, he's been teaching engineers and designers for more than 35 years.
He tells the story of how one small GD&T symbol on a drawing of a threaded hole made the difference between success and failure in a large transmission.
“One of the transmissions I worked on had two hydraulic motor mounting locations above the main gear housing. One of the motors had a 100mm long clearance hole for a 9mm diameter fastener that was inserted into a 19mm deep threaded hole."
“We didn’t check the perpendicularity of the threaded hole 100mm from the motor mounting face. The projected fastener interfered with the clearance hole so much that it compromised the thread. The dynamic motion of the hydraulic motor broke the fastener.”
“In the end, there was oil everywhere. I started using projected tolerance zone modifiers on all threaded holes and interference fit dowel pin holes. The problem was solved with one little symbol and a change in inspection procedures.”
Interpreting and analysing GD&T confidently
Expert, contemporary training in GD&T should be a top priority for any engineering, quality control, procurement or production staff in a manufacturing team.
Dr McCuistion puts it quite simply, saying, “People may die if parts are made from misinterpreted drawings.”
Tolerance analysis goes hand-in-hand with geometric dimensioning and interpretation of GD&T annotation. Calculating the range of allowable values and the effect of variations is key to excellent product design. Dr McCuistion calls tolerance stacking “both a predictive and problem-solving tool”.

Update your GD&T skills
Don’t allow your manufacturing team to be the weak link in the production chain. Engineering Education Australia is offering an upcoming virtual workshop to upskill engineers and designers in Geometric Dimensioning and Tolerancing Fundamentals, with Dr McCuistion as the expert instructor.
Delivered in partnership with The American Society of Mechanical Engineers, the workshop equips participants to apply and interpret the current ASME standards. All sessions are designed to be interactive learning experiences.
Find out more.