Dear
ASTE:
Are we simply walking shadows? Are we poor players? Do we strut and fret our hour on this stage we call life and then are heard no more? If so, I think the whole thing is a tale told by an idiot,
full of sound and fury, signifying nothing. Signed, William Shakespeare
Dear Will: Yes. Life is but a walking shadow, a poor player that struts and frets his hour upon the stage and
then is heard no more. It is a tale told by an idiot, full of sound and fury, signifying nothing. And you can quote me on that. Incidentally Will, I think you should try your hand at writing plays. Your letters show you have potential.
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Dear
ASTE: At my company our drawings are atrocious. I came here from a company that thought tolerancing
was important. Here, all we do is document the manufacturing procedure and the tolerances they hold. If the tolerances on the drawing are violated, all we do is change the drawing to what has been
produced. We even call it "reverse engineering". Well, maybe it doesn't matter anyway. After all, the original tolerances for the product weren't
calculated, just pulled out of midair. When we tolerance parts, we never take into consideration what tolerances and worst mating conditions are on the parts in the assembly that our part interacts with.
Yet, in our commercials on television and in magazines, all they talk about is the "space age" tolerances we hold. Why is it that tolerancing seems to be a great marketing tool but a joke on our drawings and on the shop floor? Dear Writer: People do and teach others to do what they know themselves. They often make fun of or downplay
the importance of the things they don't know how to do well. In college, I remember taking courses from professors on how to design parts and assemblies. I took a bunch of these courses and always
came away feeling cheated. So finally, I began asking the questions that had been bothering me. "Professor," I would say, "When I'm not in school, I work as a journeyman
diemaker. I make parts
all day long, and I've never been able to make even one perfect part. So, could you tell me please, what about tolerances? In your class we never have calculated tolerances, or even discussed how to
accurately tolerance a part or an assembly." The professors always answered me in the same way. "We don't have time for that. This is only a four year program. We must make the most of the time
we have together. We have bigger fish to fry. We are making a designer, in fact, an inventor out of you. You should appreciate the information we are giving you."
Appreciation was never my problem. I loved to learn. But I knew there was a major piece of the puzzle missing. Finally, from what I learned later on, I realized that they were teaching what they
knew. I learned that designing products and tolerancing them took completely different skills, and that just because you knew how to do one, didn't mean you knew how to do the other. They were
good at teaching and even actually doing the work of design. But they couldn't have toleranced themselves out of an ankle deep mud hole.
On the job, I found out the problem was the same. People didn't know how to tolerance anything.
Furthermore, they didn't care about it. They thought of it as grunt work. They were too important to worry themselves over lesser skills than those they provided daily. They thought that what they did was enough. But it wasn't.
Products failed, wouldn't assemble, blew up, killed people. But they all blamed others. "Its the fault of that other guy", always the other guy.
The designers blamed manufacturing, saying they all needed directions to put their shoes on the correct feet in the morning, that they should be more intuitive about the needs of the product. They
said a design drawing was, at times, only a loose set of guidelines. Besides, the tolerances didn't matter. If they had just made better parts, they would have worked fine.
The manufacturing guys blamed it on a bad design with conflicting requirements, and they blamed the people from inspection for not inspecting the parts under the same conditions in which they were to be used.
The inspectors blamed it on the designers, saying they inspected it according to the drawing requirements, but the drawing requirements were so ambiguous that they could mean anything, and
the tolerances so crude they may as well have been scrawled on a cave wall with a charred stick.
And yet, when asked to improve their technical abilities and their teamwork and concurrent
engineering skills, many of them grimaced. "Do we have to?" they asked. "We have far too much work to do. We have meetings, and deadlines, and E-mail to respond to, and fax messages to send.
You know, the real work, in the real world. Are you really going to force me to sit through a training class? I have a job to do! I'm trying to keep it real.
And the customer responds with, "Yes, you are trying to keep it real. Real stupid. Real dangerous. Real low quality. I just wanted to use your product, not be killed by it, not to have it explode in my
face or fall apart in my hands. I've seen your commercials. What happened to those 'space age' tolerances?" And the workers respond, "Oh that's just marketing. We never talk to marketing. " And
the customer says, "Apparently you never talk to manufacturing either. What's wrong? Is it too dirty down there on the shop floor? Are you afraid to ask for their advice, afraid they may find out you
don't know everything there is to know in the whole world, afraid you'll look too human, afraid you will be thought of as fraternizing with the enemy? What is it? Are you afraid they may ask you where
you got your tolerances and you'll have to show them your dart board?"
I guess the truth is not to be found in a television advertisement or on a billboard someplace. The
truth is found in the products, and in the words of the consumer, and unfortunately, sometimes on the nightly news. __________________________________________________________________ Dear
ASTE:
Is Geometric Dimensioning and Tolerancing the answer to all my company's problems as they pertain to design, manufacturing and inspection?
Dear Writer:
No, of course not. It is the answer to many problems though. Not only does it give an unambiguous design criteria, allow tolerance analysis to be easy, parts to mate in assembly with interchangeability
and make the inspection procedure meaningful by allowing workpieces to be measured in the same way as they will function, but it also gives a person an understanding of the important dimensions,
tolerances, boundaries and features that affect quality and product endurance. Among the things that interest me are the way we look at our every day jobs. Some do what they are told and don't think
much about it. Some don't do much of anything at all. Some do what they are told and grow to believe in the procedures, whether or not they have functional merit, even to the point of becoming
zealots and proponents of the procedures. Some are knowledgeable beyond the programs they are told to institute and genuinely want to improve them. Sometimes these employees are seen as
rebellious, but nothing could be farther from the truth. There is no rebellion in their hearts, only a desire to do a good job. They study what they are doing and look for ways to improve the system
and, consequently, the products and the company. These people are the curious visionaries a company needs to create a better way and survive in a competitive world.
Geometric Dimensioning and Tolerancing is a tool that is capable of giving insight to the curious. It shows how to calculate instead of guess, to deduce rather than mindlessly perform. See, I have
always believed that the people in the technical trades--those likely to be reading this--are capable of performing great feats of logic. But logic is only as good as the knowledge and experience of the one
who employs it. In order to reason things out, we need a good basis of knowledge. For a product line, this basis has to include a piece of knowledge about practically every aspect of a system. We
must make it our business to learn about the procedures our company and their vendors use in design, manufacturing and inspection. We must, in fact, learn about all the job categories that relate
or input information that directly effects the creation of the product. Otherwise, our logic will be flawed, and a piece of the puzzle that we need will be missing when we attempt to reason out the best course of
action
.
Geometric Tolerancing, when applied correctly, cuts across all job categories. It makes the Tolerancing Engineer create datums (origins of measurement and part orientation) that take into
consideration how the part fits into the assembly and how it will best function, which lends information to the inspector as to the best way to determine whether or not parts produced will,
indeed, perform as needed. GD&T allows the Tolerancing Engineer to calculate tolerances and do tolerance analysis prior to making the product, and it allows the inspector to determine whether or
not these tolerances and boundaries have been violated or will soon be violated if the same course of manufacturing is continued. It gets the people in manufacturing involved with the inspectors, seeking
their input as to measurements taken and how to change the manufacturing methods to improve the part and its measured features. It links the designer, tolerancing engineer, manufacturing people and
inspectors in a never ending discussion as to how to improve the product, its tolerances, the manufacturing methods and the inspection procedures.
Part of this is to be found in the standards of the world on Dimensioning and Tolerancing, such as the ASME Y14. 5M 1994 standard. But that is only the beginning of the process. The ANSI standards
on documentation (Y14) and measurement (B89) and their counterpart ISO (international) standards provide basic information on what tools are in the box, but the individuals and teams of users of these
documents must provide their knowledge of their products and environments to best utilize these tools. The standards are only a small part of the overall formula which makes a company and a
product line successful. But, it is a part that is essential and makes the other subsequent components of success possible.
Standards are not the answer to your problems, but they are the beginning of the
answer. The programs you employ, whether GD&T or SPC or any of a long line of programs, will only be as successful as the way they are implemented allows them to be. They need your judgment,
your knowledge, your experience and your caution. You need to take a good idea and make it better. And then take that idea and improve on it. And so on. Progress is often possible because of
people like you and me taking all of the knowledge and experience and ideas of those who came before us, and adding our little pieces of reason and logic to make the program fit our situation.
No program is going to be perfect for your system without your help. We stand on the shoulders of the giants that came before us. But all of us have the ability to, one day, be considered one of those
giants whose shoulders are stood upon by those yet to come.
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Dear
ASTE: My boss wears really big shoes. Don't misunderstand me, his feet aren't big. In fact, he is a rather
small man. It's the shoes that are big. They are so big that they curl up on the end. It makes him look like he's wearing skis, or elf shoes or something. In fact, his nickname (not to his face) around here is
Ski Boots. He not only doesn't know anything is wrong, he is so proud of his shoes that he wears pants that are far too short for him in order to emphasize the shoes. Also, he isn't a naturally graceful
man. He would have trouble even if he wasn't wearing big shoes. But with the shoes he's always stumbling around tripping over things, even to the point of injuring himself and others. Bandages have
become an expected part of his attire. When we enter a meeting with people who have never met him before, they are shocked and amused to the point that we never get anything accomplished. One
guy recently just came out with it. He said, "What's with the shoes? You lose a bet or something?" My boss was offended. He said, "These shoes cost more than your car is worth, pal. " What should
I do? This is getting ridiculous. Dear Writer: This is a tolerancing newsletter. I don't know how to solve big shoe problems.
___________________________________________________________________ Dear
ASTE:
I sit in an area without natural lighting. There are only fluorescent lights that sit in rows above my head and suck the energy from my body, and I think they are slowly draining my life away. Every
day I look in the mirror I have less hair and fewer teeth. My skin is gray and hangs loose on my bones. I am wasting away into nothingness. But, today something happened!
As I stared at my computer screen (which radiates a greenish glow that seeps into my brain and does God knows what), I noticed a ray of sunlight break across my hand (as it rested gently on my
mouse). It seemed to defy all physical laws as it crept around and through the hundreds of other cubicles to reach me. My skin came alive at its warm and sensuous touch.
My flesh grew pink, and
then rosy with actual blood pulsing beneath. I could see my heart (which I long ago thought turned to stone) beat in a rhythm worthy of a symphony. I realized at that moment that this job was killing me.
I needed to get out into the world. "What light, through yonder window breaks?" I asked. Could it be nature's message to go forth and begin anew? To start again with different priorities and goals? To
reassess the values of my existence and finally realize I have worshipped the wrong Gods? To know that moments spent with family and friends are what really matters? To appreciate every flower and
every sunset as a wonder of existence? To seek serenity and joy? To explore the beauty that I know abounds in art and music and nature, but that I have always been to busy rotting away in this tomb to
even think about? All these things passed through my mind as that single miracle shaft of light ran across my skin like it was the finger of God. And then, and then. . . . . . I came to my senses and
finished my report. It was a stupid idea anyway. A guy's gotta eat. OOPS, I just lost another tooth.
A Pragmatist in Pocatello
Dear
Prag:
I didn't know pragmatism could be so depressing. Next time you get an insight, either act on it or keep it to yourself. Excuse me, I have to go and find a field of flowers I can run barefoot through.
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Dear
ASTE:
I have a problem with the measurement of holes and shafts that are positioned to a pattern datum (a pattern of features used to construct one datum axis). It seems my Coordinate Measurement
Machine people say that they can't do what the drawing requirement means.
They say that a receiver gage could be constructed to do the job, but if the CMM is used it can't be done. They say that no
matter what appears on the drawing, they are going to pick one of the holes to measure from and one other hole to orient to. I don't get any respect around here. I feel like the Rodney Dangerfield of
dimensioning and tolerancing. Take my wife. . . . . . . Please! Oh, wait a minute, I think that was Henny
Youngman.
Dear Writer:
What it is, is old. As far as the technical question is concerned though, using a pattern of features to construct one datum axis (often known as the central axis of the MMC Concept Virtual Condition
Boundaries) can be a difficult measurement task for a CMM. Yes, they are correct in that a receiver (functional) gage would do a nice job, but it would collect no variable data. But to substitute, as they
want to do, also has its problems. The measurement of subsequently controlled features from only one feature within a pattern datum is subject to the error that one feature may experience in its
relationship to the others within the pattern. In other words, there is an accumulated error with which to deal. This error is not one that is easy to compensate for either. One can use a CMM probe on a
bunch of features within a pattern and ask the computer for an average axis. If the actual pattern of features (the real, flawed surfaces) are probed, the error can be gross, depending on the feature
configuration, orientation and location errors. However, if the part is mounted on a fixture, and the fixture is probed, the error is reduced by the amount that the fixture is better than the pattern it
fixtures (hopefully 10 to 20 times better, according to the gaging standard's recommendation of 5% to 10% of the part tolerance as gage or fixture tolerance). This fixture idea is better because the
fixturing pins represent the virtual condition boundaries (MMC of the hole minus the geometric tolerance).
Sorry about your bleak circumstances, but if the inspection folks begin ignoring the design
requirements and make up their own requirements for part measurement, you will experience a karma akin to being sucked down a black hole in space that spits you out somewhere in the sewers
of New York City. I believe you have only a few "good" choices. You could change the drawing requirements to reflect what they are going to measure anyway (make one feature a datum feature
for location and use another feature as an angular orientation datum feature), but write a drawing note that says you are going to fixture to the entire pattern for all subsequently controlled features for
measurement purposes. This, in a way, employs the concept of Simultaneous Gaging Requirements. It says that since the holes in the pattern not chosen as the datum features are controlled to the same
exact datums as the other subsequently controlled features, they must be treated as a single pattern of features and either gaged as one or fixtured in one set-up for measurement purposes. Another
option is, you could keep the drawing requirement as is and employ the use of the fixture to lessen the problem of accumulated error (by either measuring from one post in the fixture and orienting to
another, or by probing all fixture posts and asking the computer for an average datum axis. I know these solutions aren't perfect, but sometimes measurement is just doing the best you can on a
particular day, under a given set of circumstances. On a different note, you are correct in your overall assessment of life. We go through it being pushed
around, trying to keep what little dignity our morbid childhoods left us with, then at lunch one day, we choke to death on the chicken salad and our co-workers leap over our twisted, lifeless corpse,
trying to be the first to apply for our jobs and office space. It's hard being cool when rigormortis forms your hand into a claw and your "friends" begin to use it as a back scratcher or drink holder to
amuse the rest of the lunchroom crowd. Have a nice day! Your cheerful Pal, Jim Meadows
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