Nobody has to tell you that training is a valuable tool to help improve your skills and that of an entire group. But so often, a desire to implement training is thwarted by roadblocks. These roadblocks come in different forms. Here are a few, and ways to avoid or work around them...

1. RoadblockstoEffectiveTraining
Nobody has to tell you that training is a valuable tool to help improve
your skills and that of an entire group. But so often, a desire to
implementtraining is thwarted by roadblocks.These roadblocks come in
differentforms.Here are a few, and ways to avoid or work around them:
 “We don’t have time.” This is the most commonroadblock.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.
 “We don’t have anyone on staff that can teach that.” Â Well,that’s when
you get on the Web and look around for consultants! I specialize in
GD&T;other trainers have other specialties.Don’t be afraid to look
outside your company for help; if you are unsure about a consultant’s
qualifications, ask questions.How long have they been doing this? Do
they hold certifications related to the topic? (A GD&T trainer should be
ASME certified;preferablyat the Senior Level.)
 “Training is all theory; we need help using it in the real world.” Again, my
suggestionwould be to ask the trainer about this. While technical
training has a theoretical component,the instructor should be able to tie
the concepts in with actual designs or real-world situations. I always
make sure to learn a little about the company where I will be training. If
they make plastic parts, some of my presentation will be differentfrom
one at a company that makes machined engine components.Also,ask if
the trainer is willing to incorporate your actual prints into the training.
 “Our employeescan go online and get the training on their own.” This
might not seem like a roadblock,but there are two potential problems
with this. First, are they really going to sit down and do this? There are
advantages to online training for someone that is disciplined enough to
go through an entire course online. But in reality, roadblock#1 usually
creeps in here, and the training never gets done. A second issue is that
online training is usually for individuals. A live training class with an
instructor allows the entire group to be present,hear the same message,
and bounce ideas off of one another. (I love the classes where we have
designengineers, manufacturing engineers, and CMM inspectors all
together! They all leave the class with a greater understanding of their
differentviewpoints and how they must work together.)

2.  The worst roadblockI ever encountered was an HR coordinatorwho told
me that they didn’t need GD&T training because “the engineers should
have learned that in college.” I don’t have a good answer for that one! I
suppose the engineering manager should take the bull by the horns and
make arrangements for the class out of his own departmentbudget,
circumventing the HR person.At any rate, don’t let roadblocks stop your
company from pursuing technical training.
AreYou Using GD&TCorrectly?
`So often in using GD&T,people are worried about using it correctly.
And this can certainly be a valid concern — geometric tolerancing
consists of symbols and rules for how to use them. But we also need to
rememberthat GD&T is a language for communicating design
requirements.And like any other language, there may be several ways
to say the same thing.
When asked about the properuse of GD&T on a sample drawing, I
usually classify individual callouts in one of three ways: 1. A-OK; 2.
Illegal; 3. Legal, but doesn’t add any value.
Example of #1:
While the use of datum D as a pattern may seem confusing,this datum
usage is perfectlyfine.
Example of #2:
This is illegal because flatness cannot reference a datum. (Seems
obvious, but I’ve seen this several times on actual drawings!)
Example of #3:

3. This one is a little harder to assess.The feature control frame itself is
legal, but it’s actually redundant with the 0.2 provided by the height
tolerance. There is no way that the top surface could exceed 0.2
anyway, due to the plus/minus on the height dimension.
So keep in mind that GD&T is more than just learning the symbols;it
also involves many rules and the interplay of those rules can sometimes
be confusing!
TitleBlockTolerancesandGD&T
In the geometric tolerancing system,basic dimensions are used to
override general tolerances (sometimescalled title block tolerances). But
let’s investigate these general tolerances a little more closely. A sample
tolerance block is shown below, as taken from a drawing using metric
(millimeters). First, notice that the tolerance allowed depends onthe
number of digits used after the decimal. This is commonpractice; at
other times the tolerances may be divided based on the size of the
dimension(1 to 10 mm, then from 10 to 50 mm, etc.). In our example, a
separate tolerance is given for angles.
Some companies are trying to move away from these title block
tolerances. It may be because they want to define everything with GD&T
or other directmethods.While that might be OK to some extent, I would
be hesitant to eliminate the entire idea of general tolerances, for one
specificreason: the angular tolerance. Recall the old drafting rule that 90
degree angles are implied;they do not need to be dimensioned.But if
the general tolerance blockis removed,these 90 degree angles —
unless they have GD&T applied — will have no tolerance!So in your

4. efforts to improve drawings and streamline your designs,don’t go
overboard.Title block tolerances are just fine, as long as you don’t get
too lazy and let everything fall back on those numbers.
DoesGeometricTolerancingEverChange?
Many of you may know that GD&T has been around for a long time (see
an earlier blog entry about the history of this system).And like anything
else that’s been around for a while, things sometimeschange.The
current American national standard for GD&T is maintained by the
American Society of Mechanical Engineers (standard number Y14.5M-
1994).Prior to 1994,the previous edition was dated from 1982 (and
1973 before that). And each time, there were a few things that were
changed in the rules and symbols of GD&T.
So, if you look at the history of the standard, you might guess that it’s
about time for another revision — and you would be correct! The Y14.5
committee has beenhard at work for the past couple of years, and the
next edition is in the review phase. (One sneak preview for you GD&T
geeks:a new modifierto indicate unilateral profile tolerances.) It is
projected that it will be released for general use in the first part of 2009.
As a side note, this underscores why it is important to always mention
the specific tolerancing standard in the general notes of your prints, or
even as part of your company’s standard title block. If this is not
mentioned, then there may be confusionabout the meaning of some
callouts!
DoesGD&TRequireaDiameterSymbol?
Here’s another commonquestionthat comes up in a GD&T
class: Suppose we are applying a positiontolerance to a hole. It would
typically have a diameter symbolin front of the number, as in the first
example below. But what if we omit the diameter symbolin front of the
number, as in the second example? Would the shape of the tolerance
zone still be assumed as cylindrical?
Answer: No, it’s not cylindrical.
Without a diameter symbol,a tolerance zone defaults to two parallel
planes (unless the BOUNDARY conceptis invoked). So the second

5. drawing above is ambiguous; the zone will be two parallel planes, but we
don’t know the directionof those two planes.
Two solutions: First, if the intent is to control the positionin all
directions,you must add a diameter symbolas in the first example
above. Second,if we really intended two parallel planes, we must
graphically indicate the direction of those planes:
Now, it is clear that we are controlling positionin the left/right direction.
Of course,that means that there is no positioncontrol in the up/down
direction. So let’s take it one more step:
This example creates two sets of parallel planes — one in the vertical
direction and one in the horizontal direction.The result is a square
tolerance zone; thus, it’s very similar to using the traditional coordinate•
or plus/minus tolerancing method.But here we still have the advantage
of clearly identifying the datum references,and we also have the MMC
modifierto gain bonus tolerance, something that the coordinate method
cannot do.
WhatIsthe BestTimeforGD&TTraining?
Colleagues and friends often ask me what the busiesttime of the year is
for a technical training company. After teaching GD&T full time for nearly
15 years, I can honestly say that there is no specific cycle that shows up
regularly. Of course, training is rarely scheduled at the very end of the
year (Christmas holiday, and a busy time in general). But sometimes
Novemberand the first part of Decemberare very busy, because a
company or departmentmay have to use up budgeted training dollars
before the end of the year. And you might think that the summer months
are not popular for training, but they usually are, as long as it is

6. scheduled far enough in advance. (I soon discoveredthat those
companies in areas where hunting is popular usually avoid scheduling
seminars during those times in the fall when many employees may be
perched in a tree!)
This is not to say that every month is busy — like any industry, we feel
ups and downs. But from year to year, those ups and downs are rarely in
a repeatable pattern. It’s a funny thing; obviously the economydrives
much of it. But a slow time in the economycan sometimes be an ideal
time to invest in employees’technical skills: there will always be a need
for knowledge in geometric dimensioning and tolerancing. Usually, our
calendar gets pretty full at least one or two months in advance. But
sometimesthere is a window where our instructor is free,and with only a
week or two of notice, we can schedule something. So if your company
is in need of GD&T training, don’t think there is a bad time to schedule it!
HistoryofGD&T
Instead of discussing some technical point this time, let’s take a brief
look back at the history of GD&T.Some people may think that GD&T is
“just the latest fad” (I actually heard someone referto it that way) and
therefore they are implying that it’s not worth learning, since it may soon
go away. But the facts show that GD&T has been around fora long time
(50+ years), it applies tolerances in a logical and standardized manner,
and it saves money — all reasons why it’s not going to fade into the
sunset.
Supposedly,the story goes that a guy named Stanley Parker came up
with the first GD&T concepthaving to do with position(or “true position”
if you prefer).The time was World War II, and the location was Great
Britain. As you might imagine, during wartime deadlines are critical, and
Mr. Parker ran into a situation where some torpedo parts inspected
according to traditional tolerances were rejected.But it turns out that
they were actually functional parts, and those parts were sent on their
merry way even though they didn’t seem to be to print.
He traced the discrepancyto the fact that traditional X-Y tolerances
result in a square tolerance zone, but that parts outside the square may
actually be good,so long as they are within a circle that encompasses
the square’s corners:

7. See the logic? If the four corners of the square zone were functional —
as the X-Y method clearly allows — then in most cases a circular area
would be just as functional. And think how many parts may have been
needlesslyrejected!(Of course, if your processis capable, you should
not really have any parts out near the edge,but that’s a different
discussion.)
From there, GD&T has grown dramatically. Over time, Mr. Parker’s idea
of “position” grewto include other concepts such as flatness, parallelism,
runout, profile, and many more. And though GD&T became standardized
by the military in the 1950s,it gradually became more popular among
commercialindustries, and has beenused by many companies forwell
over thirty years. So don’t think of geometric tolerancing as a fad; think
of it as the way we should have always done things!
LiveGD&TTraining or“Canned”?
When it comes to learning geometric tolerancing, some people optfor
buying a bookto read, or nowadays they can sign up for an online self-
study course.The advantages to this are twofold:the ability to study at
your own pace, and it is usually less expensive for an individual than a
full training seminar.
 Traditional training with an instructor in the same room is sometimes
more expensive (not always, depending on the number of students) but
the huge advantage here is the ability to ask questions and have the
instructor relate the concepts to your specific needs.If people from
differentareas attend the class together(design, CMM inspection,
manufacturing), then they can also learn from each other and be in sync
when GD&T issues come up in the future.
 I have dabbled in online training in the past, but we have not pursued
that option in depth because we have found that the best service to our
clients is to work with them directly to help digestand retain the material.
Numerous times people have told me, “I have tried learning about bonus
tolerance in the past, but the way you explained it made sense instantly!”
While teaching a GD&T concept,I can get feedback — someone asking
a question, or just bodylanguage — that helps me see if a differentway

8. to illustrate something is needed.(For one client, I sometimes teach via
television to several of their sites across North America. It’s still not as
good as being in the same room; but at least they can ask questions via
the audio hookup.)
 Finally, in addition to teaching the concepts of GD&T,I always leave
time at the end of class (sometimes the entire last day of class) for
hands-on discussionof a group’s drawings. This consultation sessionis
usually very lively, and lets participants apply the theory to reality. This is
something an online course cannot do.
So be sure to weigh the pros and cons when investigating training
options. Online courses will work great for many people,but don’t forget
the traditional live seminar, especially if a company wants to have
several people learn GD&T.
DimensionswithDatum Targets
Another questioncame in recently, having to do with basic dimensions
and their use with datum targets. If you are up to speed on GD&T,you
should know that a basic dimensionis any number enclosedin a box:
The purpose of this is to show a theoretical dimension, without any
tolerance. (Even a general title block tolerance does not apply!) Instead,
the feature that is being dimensioned will have some GD&T that
provides the actual tolerance for manufacturing.
Now here’s the question: datum targets are usually located using basic
dimensions,but there is no GD&T to provide a tolerance:
Is this legal? What governs the accuracy of where those datum targets
are?
Yes, it is legal, and here is the key: Geometric tolerances are applied to
features of a part. A datum target is an imaginary point, line, or area that
is simply used for fixturing or gage setup. It’s not the responsibilityof a
productdrawing to worry about the tolerancing of a gage or fixture!

9. The ASME Y14.5 standard says it this way in paragraph 4.6.2: “The
location and size, where applicable,of datum targets are defined with
either basic or toleranced dimensions.If defined with basic dimensions,
established tooling or gaging tolerances apply.”
Thus, most GD&T people use basic dimensions to locate datum targets.
Of course,there is the question of where these “established tooling or
gaging tolerances” come from,but that is something for a designgroup
to discuss,and perhaps even reference in a note on the drawing.
GD&TInstructorWinsSAEAward
SAE International (the Societyof Automotive Engineers)has recently
announced its winners for this year’s awards, and among them is John-
Paul Belanger, from Geometric Learning Systems.Mr. Belanger is
receiving the ForestR. McFarland Award for outstanding contributions
toward the work of the SAE Engineering Meetings Board in the planning,
development,and disseminationof technical information through
technical meetings,conferences,and professionaldevelopment
programs.This is in recognition of his years of involvement in GD&T
training for SAE to their network of members and clients.
“I am proud of my membership in SAE, and am happy to be able to work
with them as an instructor in GD&T.They serve as a valuable resource
for the automotive industry, and I am grateful for this recognition.”
John-Paul has beeninvolved in training for GD&T and Tolerance Stacks
for over fifteenyears. He is a principal for Geometric Learning Systems,
a consulting firm specializing in GD&T training