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 unilateral (one-sided) or bilateral (both sides of the intended profile). Also realize that the profile symbols can be “unequal bilateral” where there is tolerance on both sides of the perfect shape, but more tolerance exists on one side. Some examples: No other GD&T symbol can use these options; there is no such thing as unilateral flatness or unilateral parallelism. Why is that? Well, when we talk about flatness or parallelism, the feature in question has no curvature. So the surface “is where it is.” Profile tolerances, however, have a curve (usually) and also one or more basic dimensions that describe the radius or other values. The prescribed radius is important, and if the curve dips in or out, it is directly impacting the given radius. With this in mind, I should point out the tolerance zones for some other GD&T symbols can float to one side or the other. For instance, a parallelism...
Learn MoreIf you’ve spent any time around geometric tolerancing, you have probably heard it touted as the best thing to come along in mechanical design since the drafting board. And most of it’s true — GD&T Â helps us communicate a product’s design in a big way. So it shouldn’t be surprising that most industries have adopted GD&T to some extent in their designs. Here’s a short list of some of the industries that use GD&T regularly: automotive aerospace medical devices military hardware household appliances electronic components even furniture… I admit that I have been surprised a few times by working with clients in a sector where I probably wouldn’t have guessed that they use GD&T! It is interesting, as a GD&T consultant and trainer, to work with various groups and help them implement GD&T where others may not have bothered. A few of the more interesting clients that have worked with us manufacture things such as golf clubs, blenders, explosives, gas pump handles, and even municipal water supply mains (you should see the tolerancing on the huge water valves and bulkheads!). You may have heard that GD&T is great for mass-produced parts (so a blender might need it) but not for low-volume or custom parts, such as a water main...
Learn MoreThis 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 classical method involves holding a dial indicator to the surface and then watching for the highest and lowest reading. This difference is then compared to the specification allowed by the drawing. Here’s a visual of runout being checked on an end face: The absolute value of highest to lowest gage reading is often called “TIR,” or “total indicator reading.” In the past it was quite common to specify runout by adding a note to the drawing such as “.040 max. TIR.” (Nowadays, it is more proper to use GD&T to control this, especially because the former method is ambiguous when it comes to identifying the datum.) Well, somewhere along the line another acronym crept into the vocabulary: “FIM,” which is “full indicator movement.” It essentially means the same thing — the total variation from highest to lowest gage point. But the Y14.5 standard uses FIM exclusively in its explanations for runout. Is there...
Learn MoreA 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, there are two alternative ways to meet the rule. First, if most or all of the dimensions on a print are to be basic dimensions, then a general note can be placed on the drawing that states “all dimensions shown are assumed to be basic” or something to that effect. This means that the dimension is still shown, but without the box. Caution: if this is the case, make sure that the title block does not show any default plus/minus tolerances. The other option is one that is becoming more common: Leave the dimensions off the print, and add a note saying something like “all undimensioned features are dimensioned in CAD, and are basic.” To its extreme, this means that the entire print can leave off all dimensions, requiring the reader to have access to the CAD data if they really want to know the dimension. While there are advantages to this (the...
Learn MoreThree reasons for on-site GD&T training — Why a hands-on, tailored approach is better for your team… 1 — An on-site GD&T class can be customized to suit the needs of your group. If they are immersed in GD&T regularly, we can spend less time on the introductory material and jump into the issues that are most relevant to the team. However, the basics cannot be completely avoided, because we need to make sure that everyone is on the same page for the essentials. But overall, there is more “bang for the buck” when the class is custom-fitted to the GD&T topics that are applicable to your products. 2 — Another advantage to having an on-site class is that your actual prints can be incorporated into the discussion. At a “public” GD&T class we can’t do that because everyone comes from different companies; there are time limitations, and sometimes confidentiality issues of displaying a print for the entire group to see. But a special on-site class for your team makes the GD&T relate directly to the “real world” because the instructor can help you sort out real tolerancing issues on the spot. A video or web-based course can’t do that. 3 — Contrary to what you might think, the...
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Watch John-Paul talk about the benefits of GD&T training courses.