In a GD&T class, I often talk about (and sketch) how a sample part can be held in a fixture — this helps people understand the concept of datums, particularly if datum targets are involved. This does not imply that an inspector must use a customized fixture to check a part. I refer to fixtures and physical gaging in a class simply because people can visualize those concepts, whereas a CMM is more abstract (sometimes CMMs and similar devices are called “soft gaging” as opposed to traditional “hard gaging”). If you are using a CMM, then you ensure that the probe samples the part at the prescribed datums; this establishes a coordinate system in the computer for other measurements to be made against. But wait: the part isn’t floating around in mid-air! It is still contacting something. Perhaps it is sitting on a granite table. Here’s a key point: instead of sampling three points on the surface of the part to create the datum, you should take three points on the table, since that table simulates the true datum (as derived from the high points of the part surface). The only tricky part is when datum targets are involved. This is where the designer identifies specific points, lines, or...
Learn MoreNow that the new standard has been released, the demand for training is up! And while many people simply want to know about the items that were changed or added, each training session is a chance to help folks refresh their memories about the basics of geometric tolerancing. You’d be surprised how many people who have been around GD&T for years tell us after a class that they have never really understood the difference between bonus and shift tolerance (that’s where the MMC modifier is placed after a number or after a datum letter, respectively). Or perhaps they’ve forgotten that a pattern of holes can be called out as a datum feature, rather than just one hole. Some folks are also interested in special considerations that must be taken into account for flexible parts. These are all things that are covered in our GD&T classes. But a key benefit of any “on-site” training is that it can be customized to suit your needs! Our on-site seminars can: –be scheduled at your convenience –allow everyone to hear the same message –allow participants to ask specific questions to an instructor in person –expand on topics that are pertinent to your designs, and lessen the focus on others –incorporate your drawings into...
Learn MoreWell gang, it’s finally here! The new standard for GD&T has been approved and will be shipping in the next week or two. If you’ve been around GD&T at all, you should be somewhat familiar with the 1994 standard; this new edition of Y14.5 will gradually be taking over as companies make the switch for new designs over the next couple of years. For those of you that were around when the 1994 standard was released, you may recall that there were many significant changes ranging from tweaking definitions to adding new symbols such as the triangular datum symbol (which was formerly a simple rectangular box). This time there are similar changes, although most will not be as obvious as the change to the datum symbol was. We will be offering training in the new standard! If your company needs a simple update on what’s new, contact us for information about the one-day New Standard class. If your group would like a regular GD&T class, we can do that (3 days of training) and incorporate the new standard into the class as we teach the basic concepts. Copies of the new standard can be obtained through the publisher, ASME, at this website. Of course, remember that the change to the new standard cannot...
Learn MoreA funny question arrived in the inbox yesterday, and it reminded me to get on here and post another entry. The questioner wondered if I’m undercutting some of my training business by giving out GD&T tips and explanations via this blog. Not at all. GD&T is not a secret society! It’s a very useful language and the more people that know it, the better. By explaining some of the symbology here on the blog, we hope to do two things: educate people, especially those that need assistance with a specific topic; and at the same time, generate interest in our complete GD&T seminars (wink). So it is possible to be helpful and advertise at the same time! Here’s today’s GD&T “secret”: the tangent plane modifier: First, a review of the parallelism symbol in general. The top of this block is to be parallel to datum A within .006 inches (notice that the distance between the top and bottom is a separate, more generous tolerance). Regular parallelism, without the T symbol, would require all points across the top to be within our zone of .006. But the T symbol changes things — instead of controlling every point across the top surface, now it says that the “tangent plane” formed across...
Learn MoreOK — everyone else is writing about the present economy, so I guess we should look at how it affects the training industry. I’d like to resurrect an old blog entry (about a year ago) but tweak it a little to give you all some ideas on how to sell your managers on getting people trained, even when the budgets are tight. When approaching your managers for approval on hosting a GD&T class, one form of resistance that you may get is: “We don’t have time.” This is the most common roadblock. There are always hot projects that can’t wait, especially in the world of engineering and design. But if your company considers training valuable, they should help you make time for it. To minimize the time away from your usual job duties, ask the trainer if the schedule can be broken apart. For our GD&T classes, I am willing to teach a few half-days that are spaced apart. Simply ask for this option, or see if the trainer offers a condensed version of the training. Of course, the latest version of this is “We don’t have the money.” First, emphasize that in these tight times, only the cutting-edge engineering groups will survive. And knowledge of GD&T is essential...
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Watch John-Paul talk about the benefits of GD&T training courses.