Occasionally users of GD&T suggest that everything be simplified by just boiling all 14 symbols down to just two or three. (What, you didn’t know there were 14 symbols? Click here for a handy chart!)
There is some logic to what these people are saying — namely, that many GD&T symbols overlap others, and position and profile can […]
Let’s go back to the question box –
“Why is profile allowed to be designated as one-sided? Can other GD&T symbols also be one-sided?” First, let’s address a couple of points: there are two profile symbols: profile of a line and profile of a surface. Yes, each of them can have the tolerance amount that is […]
This blog post may seem like splitting hairs to some of you, but it’s a question that came up in my class. And you know the saying: if someone has a question, chances are that others are thinking the same question.
When inspecting parts for runout (and a few other characteristics), you may know that the […]
A question came up recently about how GD&T relates to CAD dimensions: The rules of GD&T say that basic dimensions are required when using a position tolerance. But does that always mean that the print must show these “boxed” dimensions?
Answer: No, it doesn’t. While classical GD&T seems to say that the boxed dimensions are required, […]
So often in using GD&T, people are worried about using it correctly. And this can certainly be a valid concern — geometric tolerancing consists of symbols and rules for how to use them. But we also need to remember that GD&T is a language for communicating design requirements. And like any other language, there may […]
Here’s another common question that comes up in a GD&T class: Suppose we are applying a position tolerance to a hole. It would typically have a diameter symbol in front of the number, as in the first example below. But what if we omit the diameter symbol in front of the number, as in the […]
Another question came in recently, having to do with basic dimensions and their use with datum targets. If you are up to speed on GD&T, you should know that a basic dimension is any number enclosed in a box:
The purpose of this is to show a theoretical dimension, without any tolerance. (Even a general title block […]
If you are familiar with GD&T, you’ve probably heard of “virtual condition.” It is a number that represents a worst-case combination of a feature’s size along with its geometric tolerance. For instance, suppose we have the following example of a hole, with a size tolerance of 6 ± 0.2 mm: […]
There’s more to learning GD&T than just knowing the symbols. There is also a unique vocabulary – sometimes GD&T terms mesh with everyday usage, but sometimes a word can have a very specific meaning in geometric tolerancing.
Here are some examples:
The symbol circularity is sometimes called roundness. The two terms are synonymous, but the ASME standard uses circularity.
The most common […]
Here’s a question I received at the beginning of a recent GD&T training session. Often I’ll ask participants if there is anything in particular that they are looking to get out of the training. One gentleman didn’t hesitate:
“I’m here to learn why we shouldn’t use the concentricity symbol. No one has been able to tell me […]
