Posts by jpbelanger

Virtual training vs. In-person training?

Posted by on Feb 3, 2021 in GD&T Training Options, Uncategorized

There’s no debate that things were shaken up by COVID in 2020. And certainly in the training world, adjustments had to be made! While online training has been around for many years (I’ve been doing some form of online training for 20 years), the option of virtual, live training became the norm in 2020. Now that things are somewhat back on track, the question we hear is if traditional, in-person training is still better. The short answer is yes, it is better for a number of reasons — the biggest reason is that it’s simply more effective. When using Zoom, WebEx, Teams (insert your favorite meeting platform here), there is an unavoidable detachment that creeps in, even if the participants are super-excited to hear about the topic! And as an instructor, I can’t read the body language of participants, so it’s harder to draw into the discussion those who might be a little more shy. So I suspect that very few people will disagree with me that a traditional-style class is still the best. But there is still a place for virtual training (and we continue to offer that option if a client really prefers that) because it can be more convenient and is often less expensive. Plus, your...

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Projected Tolerance Zone: Equivalent to Tightening the Zone?

Posted by on Feb 26, 2020 in Uncategorized

If you’re familiar with the different GD&T modifiers, then you probably know that the circled P creates a “projected tolerance zone.”  This is often used on threaded holes to keep any fastener that protrudes beyond the threaded hole from causing interference with a mating part: Without the “P” modifier, the tolerance zone exists only within the depth of the threaded hole itself.  The result is that the threaded hole could tilt, and be passed for position tolerance, yet cause interference: So “P” is a good thing.  However, when this concept is presented in our GD&T classes, someone will occasionally ask if we could — as an alternative to “P” — simply tighten the position tolerance number instead.  The dialog might go like this: “Couldn’t we just change the 0.3 to 0.2 (or 0.1) and achieve the same effect of preventing too much tilt?” “Yes, that would be legal,” I answer. “But using the P allows us to keep a larger tolerance, while preventing interference.” “But it has the same effect of tightening the position tolerance anyway,” the student might reply. This is where we have to be careful.  It’s true that projecting the tolerance zone has the effect of tightening the perpendicularity aspect of a position tolerance (because it’s extended higher), but it still...

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The New ASME Y14.5-2018 Standard

Posted by on May 24, 2019 in 2018 ASME standard

Well, an updated version of the GD&T standard has been released! Although released in 2019, it carries the date of 2018 (big things move slowly, right?) For those of you who use GD&T regularly, it’s probably worth the money to buy the new standard from ASME (either hard copy or PDF — same price). I’m still absorbing some of the changes, but for now I’ll mention a couple of significant things… The most notable change is the deletion of concentricity and symmetry from the standard. You may already know that these two symbols have been confusing, because they were often misused or misinterpreted. (See our past blog post here for a glimpse into concentricity.) So now the main choice for location will be position, but profile or runout symbols can also be used to control coaxial features. …there are some other things in the new standard, but these are the main ones for now. Another change to the standard was the addition of a new modifier called “dynamic profile.” It’s a little triangle symbol that can be placed within a profile’s feature control frame (after the tolerance number), and it means that the profile zone controls form (which profile usually does) but not the size of the feature. For...

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Common Dimensioning Symbol Errors

Posted by on Apr 23, 2014 in Uncategorized

No matter how good a dimensioning system is — GD&T, anyone? — there will still be errors encountered on drawings, simply because there will always be human beings who are behind the creation of a new drawing.  And of course we all make mistakes.  But I want to point out a few of the more common mistakes that I encounter in my travels. •   Failure to include a diameter symbol in a feature control frame when needed.  I’m thinking particularly of position and perpendicularity. When tagging these tolerances to a hole or pin, you usually need to include the diameter symbol before the number, so that the axis of the feature is contained in all directions. There are times when a hole’s position tolerance should not use a diameter symbol: if you really only want the tolerance to apply in two directions.  But that must be clearly indicated by proper using of dimension arrows.       •   The next common error I’d like to review is similar to the first — using a diameter symbol when it shouldn’t be there!  I see this in feature control frames for circularity, cylindricity, circular runout, and total runout.  It might be tempting, because each of these is applied to...

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Words Are Important

Posted by on May 26, 2012 in GD&T questions

Ah, yes.  I remember as a child being told that words are important!  And that is certainly true in the world of geometric dimensioning and tolerancing.  So many people think that GD&T is just a matter of learning the symbols, and it’s true that that is a key part of understanding the language.  But behind the symbols are many rules, acronyms, and definitions that can make a great difference if they are not fully understood. One of the most significant examples is the confusion about the term concentricity. To a casual beginner, the word “concentric” sounds like a simple idea: two or more circles that share a common center.  But in the world of GD&T, concentricity has a very specific meaning that is more specific than what you’ll find in Webster’s Dictionary!   FYI — the same confusion applies to the symmetry symbol. (For more about concentricity, see this blog entry from a couple of years ago.) Here are a few other miscellaneous terms to be careful with: Datum — Technically, a datum is a perfect plane, axis, or point (or combination of these).  So when talking about the actual surface of a part, we shouldn’t call it “datum A,” because that surface may be imperfect: slightly concave, convex, etc.  The...

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