Geometric Dimensioning
& Tolerancing


Heather Lamming

Heather Lamming
CEng MIMechE

Dave Masson had spent so long in industry at so many different companies with so many different products; he really does know the subject. This meant that the sometimes-abstract concepts covered in the course could be illustrated with real world examples that brought the ideas to life.

Verified by an engineer

As a Principle Mechanical Design Engineer at Siemens Energy, Heather Lamming is part of a team that designs 3D printed parts for gas turbines. Based in the engineering giant’s Lincoln office, Heather describes her role as “realising wishes from different kinds of engineers and analysts to create the functional component”. The job sees her designing parts and inspecting her colleague’s drawings, as well communicating with other Siemens engineers and specialist manufacturers to produce parts – all of which makes the work “highly collaborative”.

It’s a job Heather has relished since joining Siemens in 2015, after spending the first eight years of her career at a bespoke bearing manufacturer. Heather holds an MSc in Engineering Design and Manufacturing from Loughborough University (2012) and a BSc in Mechanical Design and Manufacturing from Plymouth. She received her MIMechE CEng accreditation in 2019.

In May 2022, she attended a three-day GD&T course which focused on the European-focused ISO standard (as opposed to the North American ASME standard that the IMechE also offers training for).


Why Geometric Dimensioning and Tolerancing (GD&T)?

Heather lists the reasons she wanted to learn GD&T.

Partly, it was to fill a knowledge gap: “having been an engineer for 14 years or so, I guess I didn't really have an understanding of it”. In her previous job, the components she designed were relatively similar, which meant that there was little need to use a system like GD&T to communicate engineering tolerances. By contrast, at Siemens she works with a “broad spectrum” of parts. “I don't just deal with one type of component; I could be dealing with several different components of an engine. So, they'll all have a different function and therefore, you come across a lot more [need for] GD&T”.

Practically speaking, Heather was conscious that Siemens was producing many different parts and wanted to ensure that they would be manufactured correctly first time. “I wanted to make sure that on our journey to having these additively manufactured components that they would fit their purpose”. Learning GD&T would help reduce the risk of miscommunications.

Finally, getting the accreditation would add value to her team’s work and her own skillset. There are only a couple of people in her office who know GD&T, “so I wanted to be one of those people”. 

What was your experience of the course?

Heather attended a three-day ISO GD&T course in May 2022 led by Dave Masson MIMechE, a design engineer who has decades of experience in industry. The course took place in-person at the IMechE’s London HQ, with 11 other students (making it a full class).

Heather explains that the first day was theoretical, introducing “how the standard works, and how utterly bonkers it can seem at first!” She learnt about GD&T’s terminology and the logic behind its pictorial symbols.

On days two and three, the students delved into the language in more depth. They learnt about the data and references, specific GD&T symbols, and how to use them on a drawing to build up a tolerance framework.

Besides the course content, Heather says she particularly enjoyed the teaching. Course tutor Dave Masson had “spent so long in industry at so many different companies with so many different products; he really does know the subject” she says. This meant that the sometimes-abstract concepts covered in the course could be illustrated with real world examples that brought the ideas to life.

Heather adds that the course training aids were useful too: “we were passing all sorts of different components around, and you could look at them while he was talking to you and get a handle on it”.

What are the three reasons why someone should attend a GD&T course?

  1. Provides a good practical and theoretical understanding of GD&T and how it can be applied.
  2. Very helpful in design engineering roles where several engineers may have made changes to a drawing.
  3. Learning GD&T is particularly helpful when working with external manufacturers who need clear instructions.

What impact has the training had?

“I was surprised that it would come in handy so quickly!”

Just a couple of weeks after completing the GD&T course, Heather found herself reviewing a drawing that another engineer had helped draft. “I pulled it out, and I looked at it and I thought to myself ‘is this drawing ambiguous? Does the drawing represent a fully functioning component? Or can it be misread in any way?’”

She felt there were some parts of the drawing that could be misunderstood by an external manufacturer, so she “added a few extra GD&T symbols to clarify everything and make sure that it couldn't possibly be misinterpreted”.

What’s next?

Heather says she would “100% recommend” the course. In her role as Principal Mechanical Design Engineer, she regularly checks other people’s work and so knowledge of GD&T will be very valuable as her career progresses.

In future, Heather plans to do a further IMechE course on Tolerance Stack Ups to develop her skills in this area. She also hopes to work towards promotion at Siemens as a Lead Engineer.

Geometric Dimensioning and Tolerancing (GD&T)

  • Duration:
    3 days
  • Location:
  • CPD Hours:
  • UK-Spec:
    A, B, C, D, E