GD & T Training

Hi guys,

My manager wants me to become an expert in Geometric Dimensioning &
Tolerancing over the next year.
My question, do I enroll in a seminars based program or do I order the
GD & T Trainer on CD where I can learn at my own pace?

Thanks
cadguy13

 

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

 

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 www.sme.org 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.


--

*****************************
From Roger Meloche

*****************************

 

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