GD & T Training

I taught GDT for several years at the university level as well as to several of my employees. For long term GDT understanding you should start off with a class of some sort. Hopefully the class will provide you with some books or trainer CDs. If not, you should definitely buy them. Learning is one thing, longer term you will need to remember how to use the more obscure GDTs. At that point you'll need to have a good reference book. I have purchased several of these from Amazon, some of which were very good and some of which really stunk. I don't have any of these books anymore as I left them with my last company (they paid for them) so now I use the limited explanations in the Drawing Requirements Manual. If I recall corretly a decent book was "Geometric Dimensioning and Tolerancing" by Alex Krulikowski. It is formatted for a class with quizes at the end of each section. I don't remember the really bad one's name or author, but it had a yellow hardcover with a drawing of a heavily GDT'd widget. This book is more of an esoteric discussion of GDT, not laid out in any particular order or of any value as a reference. It was obviously written by someone who knew GDT inside-out but had no idea how to convey that information to others.

Good luck, Mickey

"cadguy" wrote in message news: snipped-for-privacy@posting.google.com...

Take a class, but go prepared. You can get a book or two to get familiar with the GD&T concepts, do practice problems, apply it to your current projects as practice. But with a class (ka-ching$$ gonna cost you) you actually get to play "stump the teacher" and get answers to real life weirdness.

Look at the Society of Mfg Engrs

they have a wealth of online/onffline/seminar training to offer (but it ain't cheap).

Moe & the guys

Take a class definately, I have been using GD&T for over 30 years, taught by the experts at Rolls Royce, but still get it wrong. (occasionally) One fallicy is that GD&T is an unneccessary evil, wrong, used correctly it will cut the scrap rate down on complicated parts drastically. GD&T is best used where you have complicated, precision machined mating parts. Only one thing worse than someone who doesnt know GD&T, and that is someone who thinks he knows GD&T. GD&T is used widely in the aerospace industry, but I still get a kick out of hearing two knowledgeable engineers arguing over it.

I just thought that I would add my two cents. Feel free to disagree.

I've come across many product drawings over the years and seen some wild stuff! Generally, GD&T directly reflects the manufacturing process and the actual function of a part, rather than it's physical form. It's used mainly for production parts, but can also be used successfully for one-off parts and machines as well. Here are a few general rules that I use when applying GD&T.

-The purpose of GD&T is to REDUCE overall tolerances and manufacturing costs. If your part is getting more complicated and/or expensive, then you are either not applying it correctly, or you don't need the GD&T. For every Geometric Tolerance added, there should be a few other tolerances opened up.

-Concentrate only on the key function of the part and it's critical features and hold these only as tight as necessary.

-There is usually more than one way to specify a functional characteristics of a given part. Select the one that best suits the actual machining or manufacturing operations performed on the part. If in doubt, use the simplest method.

-Always keep in mind how these tolerances will be measured and verified. Production gauging can become very expensive, and one-off parts can be tricky to check if you don't have a CMM in house.

-For most turning (Lathe) operations, I use Circular and Total Runout to instead of more complicated tolerances like Perpendicularity, Cylindricity, etc... The parts can be more easily measured, and the results are the same.

-Keep in mind that positional tolerances are based on radial tolerance zones, not X-Y deviation. This means that you can open-up tolerances and maintain functionality. Production & NC machining can work well with this, however, I wouldn't recommend using them in a standard machine shop.

I hope that these pearls of wisdom are of some use to you. Some people may disagree, but these rules work well for me.

try this one

Hi Cadguy!

In addition to any training you get, obtain the ansiy15.4m spec and study that in depth as well. Training, yes. A mentor, if avialable. Becoming intimate with the actual spec, absolutely.

(mini sermon) GD&T is a great tool although not a panacea for misguided manufacturing expectations ----> GD&T won't make impossible parts easier to make(sermon over - smile).

Get the spec for sure- It all starts there.

Regards-

SMA