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The Tolerancing Engineer Newsletter - April, 2012
...by our client company personnel and James D. Meadows using our ‘GD&T HOTLINE’

2012 PUBLIC WORKSHOPS with James Meadows

 

Course: Geometric Dimensioning &Tolerancing [per the ASME Y14.5-2009 and 1994 Standards and the Differences between them]  

Dates:  December 9 - 11, 2013  (2 ½ days)

Fee: $1,410 per person prepaid [see below for discounts offered]

Location:  Bevill Conference Center & Hotel, 550 Sparkman Drive,  Huntsville, AL 35816, (256) 824-4721

Hours: 8 a.m. – 4 p.m., except for half-day session (includes lunches except on half-day session)


..and/or


Course: Advanced GD&T [per the ASME Y14.5-2009 and 1994 Standards]

Dates:    December 11 - 13, 2013  (2 ½ days)

Fee: $1,410 per person prepaid [see below for discounts offered]

Location:  Bevill Conference Center & Hotel, 550 Sparkman Drive,  Huntsville, AL 35816, (256) 824-4721
Hours: 8 a.m. – 4 p.m., except for half-day session (includes lunches except on half-day session)

Based on course or courses registered for, Attendees Receive:

text Geometric Dimensioning and Tolerancing  - Application, Analysis and Measurement [per ASME y14.5-2009& 1994]  and the Workbook and Answerbook for Geometric Dimensioning and Tolerancing [per ASME Y14.5-2009 & 1994] © by James D. Meadows for the GD&T courses (Basic and Advanced)   

● Certificate of Course Completion

● use of  our invaluable  GD&T 'HOTLINE' after training for answers to student technical questions.

 

Discounts: Government organizations and government contractors = 15% discount per person; any organizations sending 3 or more attendees = 15% discount; any organization sending 7 or more = 25% discount.  Only one discount can apply.

 

 

...these are reprints from a few 'old' emails--has anything really changed?


...reprint from 1997
Dudes

Like what is GD&T? It sounds pretty cosmic. Does it have to do with channeling? I know this chick who does a transformation into a three thousand year old warrior from Atlantis who has lived on in the winds of time and space. He's called Gaga Din Tin or GD&T for short.

Dude, Mississippi

Dude!
Do they let you talk like that in Mississippi?
 



...reprint from 1997
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.
 



... reprint from 2002
Dear ASTE:
We make products that are unique. We don't make hundreds of thousands of parts that have to interchangeably fit into any machine we make. Therefore, it not only seems to me that we don't need Geometric Dimensioning and Tolerancing, but we don't need tolerances at all. When we get a part in from one of our vendors, we just grind it until it fits into the assembly. What benefit does GD&T have for us?

Satisfied in Syracuse

Dear Satisfied:
Just how much time is spent grinding things to fit? Wouldn't it be more efficient if you were able to just take the parts as they come into your facility and assemble them? And what if one of your machines breaks down when your customers are using them? How can you ship them a replacement part? It seems to me that although having parts that fit interchangeably offers many benefits for those making thousands of the same thing, it would beat the heck out of all those "grind to fit" situations you are so satisfied with even if you do make only one of each.
 



...reprint from 2002
Dear ASTE:
I believe that cell phones mark the end of civilization as we know it. People may as well walk around with these things surgically implanted in their craniums. They drive and talk, eat and talk, talk and talk. Talk, talk, talk! Is it really necessary to call someone from the video store and describe every single movie in the store? Do you need to call from the bookstore and read the book jacket to everyone in the house? If you go to lunch with someone, shouldn't you expect to talk to him or her, instead of watching them dial number after number and discuss any inane thought that jumps into their big, old, empty head? These things ring in training classes, in theaters, in malls, in restaurants, and even in elementary, middle and high school classrooms. And no matter who is being disturbed and interrupted by them, these people are compelled to answer these ringing or chirping irritants and say earth-shattering things like, "Not much. What's up wit chu?" These people are so desperate to make everyone around them believe others are in need of their contact that they could be standing next to a real person and refuse to talk to them unless they could call them on the cell phone. It's pitiful and irritating!

I was standing in line behind several people waiting to rent a car at the Dallas Airport and the guy at the counter could not tear the customer there away from his phone conversation long enough to get the information he needed to get the line moving. A huge southern boy that was behind the "talker" put his hand on his shoulder and offered to shove the phone up his…well never mind. But suffice it to say the rest of us began to spontaneously applaud.

On one of my recent flights, a flight attendant had to rip a cell phone from the ear of a passenger, just so we could take off. He absolutely would not do it on his own.

What's wrong with everyone? Have they lost their collective minds? No one cares very much that you are in the car, three blocks from home, now two blocks from home, now one, now pulling up into the driveway, now opening the door. My God! Give the rest of us a break! I can't take it anymore!

Dear Reader:
I'm wit chu. I've had to take people by the arm and lead them out of seminars I've conducted, and they were so wrapped up in their cell phone conversations that they didn't even realize they were being led out and talking louder than my lecture. And, furthermore, they acted surprised and insulted when they found they were temporarily ejected just so the rest of us could get on with our trivial seminar.

And, yes, they were actually saying things like, "Not much. What's up wit chu?"

Jim
 



...reprint from 2004
Subject: ASME Y14.43-2003
Dear Jim,
I have received a copy of the "Dimensioning and Tolerancing Principles for Gages and Fixtures" (your hard-earned masterpiece). Please accept my most hearty congratulations to you and that 'first team' committee for a magnificent job and in 'finally' providing the methods, rules, guidelines and direction for the gaging community to do its job better than ever before. New horizons have now been supplied and tutorial guidance for all from beginner to expert are there. The new and necessary ground now broken for the benefit of all users and the gaging/manufacturing profession, can better proceed into the future with greater confidence; it now has "a home of its own". The sort of 'guessing game' basis of the past in gaging principles, now has a nucleus of authority and a point of departure for the future. Be prepared, of course, for the dialog, criticism, challenges and maybe changes for improvement forthcoming in the future life of the standard. Such are really a form of flattery and departures for possible new progress with a stronger and more knowledgeable using constituency. A permanent vehicle on the subject is now there for all the world to see. The feeling of a job so well done will give a long lasting good memory.

Enjoy the 'victory', you have all earned "ownership" of a new ASME Standard. That is a real accomplishment! ; with the rewards, as you well know a bit intangible but very real' into the future.
Thanks again and best regards to all,
Lowell Foster

Thanks, Lowell.
We learned a lot. And we learned much of it the hard way. I shouldn't have gotten mixed up with the B89 committee in the first place. Little did I know that they had an agenda from the outset. They wanted to squelch any standard on gages, so that they could pretend like CMM's are the only measurement method acceptable to ANSI and ASME. I always thought both were necessary, each having unique abilities lacking in the other.

But we won. We were going down in flames, however, until you rode to our rescue. I didn't mind for myself so much. I've always had a willingness to dive off a cliff, if I thought a wrong was being done and the only way to alert others was to commit political suicide. But I felt bad for the others on our committee that dove over with me. I was surprised when so many did. Still, we just didn't have the clout to win. We had only the ability to make a lot of noise and make people mad. I was ready to settle for that. Then you started writing letters and opening doors. I thought my letters were stinging, but your letters to B89 were like daggers. I know if it weren't for your influence, we wouldn't be a Y14 standard. It was like suddenly discovering you have a big brother willing to stand up for you. I really appreciate your efforts on our behalf and I'm certain the other Y14.43 members feel the same. There was a phrase I remember from Y14.5 (and you, in particular) in years past. It was, "Fighting the good fight". To me it always meant doing the right thing in the face of adversity. I think this time, a good thing happened, in spite of bad people. And we owe much of our success to you.
Thanks again.
Jim
 

 



New Letters from 2012

Subject: Runout


Jim,
I have a cylinder with an inside diameter of 1.629/1.631 with runout of .005. Is the MMC 1.629 minus .005 which makes it 1.624? (FYI, the outside diameter of datum “A” is 1.800/1.802).


Hubert

Hubert,


The MMC has nothing to do with the Runout tolerance. It is still 1.629. However, if you want something stationary to fit inside of this I.D. while the I.D. is rotating, it will probably have to take the runout into consideration. So, in that case, you would be interested in the “inner boundary” which is 1.624.


Jim
 



Subject: Positional Tolerance and Runout


Jim,


When doing a stack up you have a positional diameter tolerance .010 in your feature control frame, do you convert the true position to a plus and minus to implement into your stack up (Aerospace designs in inches)? Another question, I thought runout had to be within size limits, but on page 488 in your newest textbook, the runout tolerance of 0.2 was added to the OD MMC of 251 which made it 251.2 for an outer boundary. Am I interpreting this wrong?


Bob

Bob,


No, for the methodology I use in my book on Tolerance Stack-Up Analysis, you don’t convert it to a plus and minus tolerance in the way you are thinking. You calculate the outer boundary and the inner boundary using the size and any applicable positional tolerance, then find the mean dimension by adding the outer boundary to the inner boundary and dividing that number by 2, and then you subtract the inner boundary from the outer boundary and divide that by 2. These calculations reveal the mean dimension and the plus and minus tolerance for it that you insert into your stack up analysis.

Runout tolerance is not to be held to within the size limits. It is additive. Size tolerance does not control how far off center diameters can be to one another, so runout is additive in a rotational state.

Jim



Subject: Bonus Tolerance vs. Datum Feature Shift


Jim,


Is it possible in calculating things like wall thickness to implement datum shift and bonus tolerance together, or do you figure each separately? For example, when each carries either a Maximum Material Condition symbol after the positional tolerance or Maximum Material Boundary modifiers on the secondary and/or tertiary datum features? Is there a page in your gray book that identifies this?


John

John,


Both can affect wall thickness, but are different phenomena.

Bonus tolerance, due to the maximum material condition symbol used after a geometric tolerance, allows an increase in the individual (for example, position) tolerance for a feature. If we were talking about a hole pattern with position tolerance, bonus tolerance would allow more movement of the holes away from each other or more movement of the group. In other words, the holes within the pattern would experience more position tolerance that would allow them to spread away from each other or to move as a group away (or toward) the datum (axis or centerplane).

Datum feature shift due to the maximum material boundary symbol after a datum feature in such a position control would not add to the individual position tolerance of the holes within the pattern. In other words, datum feature shift wouldn’t allow the holes within the pattern to spread farther from one another. It would only increase their movement as a group from the datum.

As far as the gray textbook covering this, it covers it over and over again. One of many sections covering this goes from page 142 through 145. Another goes from page 89 through page 92.

As far as how it affects wall thickness, see pages 314 through 320.


There are many more pertinent sections, but that should get you started.


Jim
 



Subject: Profile Tolerance inspection using CMM


Hi James,


I'm really enjoy reading all about GD&T in you books. I'm hoping, one day I could meet you and attend your training course.

Anyway, I need your help to get more understanding as follows:

Our CMM measured the surface profile and the results are shown below:
Point 1:
X nominal=10
Y nominal=20
Z nominal=30

X actual = 10.1
Y actual = 20.1
Z actual = 29.8

X deviation = 0.1
Y deviation = 0.1
Z deviation = 0.2

Profile tolerance call out is 0.5. Actual profile tolerance (software generation) is 0.489.

After checking, the software is using the formulae as: Profile tolerance= 2 times the square root of the deviations of X² + Y² + Z²

Just to confirm, is the above formula generated by our software correct or wrong? If wrong, what is actual formula?

Thanks again for your help…Richard

Richard,


To calculate a point’s deviation from its basic location in space in terms of a total width or diameter (for an equal bilateral tolerance zone), the formula is correct. However, there are other ways to express a profile’s deviation from basic. For example, it could be expressed as a radial deviation from basic, using the worst case for the largest plus deviation and the worst case for the largest minus deviation. The formula would then be the same, but to express each as a radial deviation, the “2 times” portion of the formula would be eliminated. This would tell you the direction of the deviation and the amount of maximum deviation in both the plus and the minus directions reported separately. Also, if the profile tolerance isn’t equal bilateral, but rather unilateral or unequal bilateral, the formula would not show the deviation from the mean profile, since the mean profile isn’t shown.

The formula you are using is normally used to calculate the deviation from true position of the axis of a sphere. The software writers for your CMM have apparently used it to find a profile of a surface deviation of each point on the surface individually. Again, this would only work if the tolerance of profile was equal bilateral, and you wanted to express the deviation as being out an amount that could be directly compared to what is in the profile feature control frame. This formula is adequate in some cases, but wouldn’t tell you much about the deviation. For example, it wouldn’t tell you which way the point has deviated from basic and to even tell how much it has deviated radially, you’d have to divide the answer by 2.

By the way, there is an ASME standard numbered Y14.45 currently being written to show how variables collected data should be reported. Until it is published, there is no standard rule on the reporting of measurement data.


Hope this helps,


Jim
 



Subject: Composite Surface Profile Tolerance


Hello Mr. Meadows,


I have a little question concerning a composite surface profile tolerance. We have 2 of your excellent books, but I can’t find the answer in there, neither can I find it in ASME Y14.5 – 2009.


We have the following tolerance in the CAD-model:





The lower level control frame indicates a surface profile to control the form on a unit basis, but how should we interpret this?
Does it mean the tolerance has to be evaluated in zones of 5” X 5” (a) or is it in zones of 5” on the whole width of the part (b)?
a) Tolerance evaluated in zones of 5” by 5”


b) Tolerance evaluated in zones of 5” over the whole width (8.37”) of the part, this means zones of 5” by 8.37”


Thanks in advance,


Marc

Marc,


This is a really interesting question. Years ago, Y14.5.1 (the math committee) pointed out to the Y14.5 committee that straightness of a surface had the problem of not specifying the angle that the control applied in. It relied instead on the control being applied in the plane of view it was shown in. In essence, it was argued, that this constituted an implied datum and wasn’t legal. It was suggested straightness of a surface be allowed to reference datums to give us the orientation of the control. The Y14.5 committee was against straightness referencing a datum and suggested that if we wanted more clarity of the orientation of the measurement, we use profile of a line which allows datum references.

If this was straightness and we applied that interpretation, we could say that the control applies in the plane of the view that it is shown in. But, this isn’t straightness. It’s profile.

What I can say is that, since this is profile of a surface, this is more like flatness on a unit basis. In a flatness of a surface control, whether it has one level of control only, or it has two levels (one an overall large tolerance and then a smaller tolerance for a unit basis control), the orientation of the application is in any and all directions. Since this is profile, they should have given the unit basis control datum references, so that we know what orientation to use when the part is measured. Lacking that, I would say that the plane of the view the control is shown in is your only guide as to their “intent”. The problem is that it could easily be argued that it applies in any orientation of measurement. Also, they didn’t say 5.0 X 5.0. If they wanted it to apply in areas of 5.0 X 5.0, they should have specified that. I would assume they wanted it to apply over 5.0 increments (beginning anywhere) and extending over the entire part.

Still, I would feel a lot more comfortable saying what they intended if they had included datum references to control orientation. What makes this even more interesting is that there is no example in Y14.5 of profile of a surface using a unit length control (two levels of control sharing one geometric characteristic symbol-the upper level controlling overall form and the second level controlling form over a unit length). Still, that doesn’t make it illegal. There are, however, provisions allowing profile of a surface composite controls (one symbol sharing two levels of control). In these, like composite position controls, any datum references used beyond the first level of control is, by definition, incapable of location and can control only the orientation of the measurement. In these composite profile controls, the upper level tolerance usually locates and orients the profile of the surface to the datums, while the lower level (smaller) tolerance refines the form of the surface and tightens the orientation to any datum references (if any) that are used.

As I said, this is interesting stuff.


Jim

 

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