From the time the first engineering drawings were created, manufacturing tolerances have existed. Tolerances allow parts to deviate from nominal within specified limits.

The function of the part and system capability drives the designer to allocate the ‘acceptable’ amount of deviation to the perfect part, while ensuring mating parts fit properly and function as intended. The goal of tolerancing is to achieve the best balance between high cost with tolerances too tight, and low cost with tolerances too loose. Traditional tolerancing methods were simple – every dimension had a ± allowance. If the drawing dimension stated: 10.00mm ±0.10mm, then an acceptable part would measure between 9.90mm and 10.10mm.

Progression in the engineering process and part design drove a new method of implementing tolerances: geometric dimensioning and tolerancing (GD&T). Using relatively simple tools, GD&T allows for more comprehensive, consistent tolerances for key dimensions, with a focus on part function and feature relationships rather than the traditional ‘trial and error’ approach. The benefits of GD&T are well documented and wide-ranging: it helps avoid rejection of functionally acceptable parts, simplifies gage design, allows for bonus tolerances for increased part acceptance, improves the quality of your product, and maximises efficiency through every stage of the manufacturing cycle, to name just a few.

Despite the clear benefits, many engineers were still reluctant to adopt GD&T for their product. Unfortunately, many mistakenly viewed GD&T as making tolerances tighter, parts more expensive, or that GD&T is not applicable to their product or was too difficult to learn.

The introduction of coordinate measuring systems such as fixed and portable CMMs, 3D scanners and video (vision) inspection systems went a long way to alleviating some of the perceived complexities of GD&T, with measuring and reporting of even the most complex of GD&T requirements being as simple as ‘click and report’. Now we are seeing a growing number of manufacturers adopting GD&T throughout their product range; from the very basic to the most complicated parts.

The advantages of GD&T are being embraced at all levels of organisations. Ease of measurement utilising this type of equipment may have helped solve the measurement dilemma, but in many cases the interpretation of the results and what changes need to be made (either to the process or the design) would become the next sticking point in the process.

GD&T itself is not complex and introducing a broader knowledge base of GD&T for employees – from managers to designers to the shop floor – with even a basic level of understanding of GD&T will improve workflow and efficiency throughout the organisation and help overcome some of the confusion that still seems to plague many organisations.

Hi-Tech Metrology recognises this need and offers training programs with hands-on exercises in GD&T using coordinate metrology, bridging the gap between engineering requirements and interpreting the measured result, and assisting many companies in their GD&T evolution. Approaching GD&T from a simplified and practical viewpoint will dispel some of the myths preventing companies from experiencing its benefits, while also assisting organisations in the overall understanding of their manufacturing processes.