ASME Y14.5-Next may be better for nubies...

[ptruitt]

Perhaps some of us come to GD&T with too much baggage. I am hoping that ASME Y14.5-Next will take away some of the redundant symbology and hand out datums only when simultanaity is insufficient. Less is often better, in my opinion. A thread 100 posts long with many very capable minds in turmoil is not something to allow in the next Y14.5. The more nubies we can save from such a grim future, the better.

Peter Truitt
Minnesota

 

[MechNorth]

Fair enough, J-P. Unfortunately I've tended to not use 0(M) as much as I could/should have because too few people understand it; arguably a poor reason, but a reality that we all live with.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[fsincox]

I think we all understand the theory; we all don't use it as much as we should. That is directly related to the issue here, the screaming shop. It also makes the point that those of us who do understand it, know it is an education problem not a tolerancing problem. Just like my issues with RFS or MMC on threads, they want MMC, when I say just put a fastener in it and measure it, No they don’t want to take the trouble to do that either, but, it is right in the book and generally what we want!
Frank

 

[ptruitt]

I get what you guys are saying with the 0(M)perpendicularity. Nevertheless, I find the concept of composite profile tolerancing to be more straightforward. I doubt that nubies would get the idea of 0(M)perpendicularity quicker. I do understand that using 0(M)perpendicularity facilitates bonus tolerance.

Peter Truitt
Minnesota

 

[fsincox]

Peter,
Do you mean to apply as an "all around" thing, or just the holes. Isn't part of the problem the implication of prefection the envelope principle trys to invoke also?
Frank

 

[ptruitt]

I am refering to using a composite profile tolerance for the holes, Frank. If simultanaity is not sufficient to orient the holes with respect to to top and bottom of thin sheet material, then make one side of the sheet Datum A and orient the hole to it in one or more fcfs.

Peter Truitt
Minnesota

 

[MechNorth]

Peter,
You won't get any argument from me about using Profile in this scenario. The shop ... well, that's another story.

On the topic of 0(M), though, education is, indeed, the issue. Depending on the group, I teach it different ways. I often show one of our training slides with 0(M) on it and go ... "well that's not right, is it!...Or is it? What are they asking for here?", and then lead them thru the exercise. Gets'em every time, doesn't matter if it's design, shop or inspection (and even management gets it too!!!). After that, they're converts. Problem still arises when I don't have the entire food chain in my classes ... bogs down when one of the groups is missing.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[fsincox]

Peter,
As a flat sheet or as formed?
Frank

 

[ptruitt]

At the moment, I was thinking of a constrained-to-a-flat profile. (Possibly constrained by gravity, if we are talking about a film.) In the case of formed sheets, spelling out orientation with a datum structure (if rigid) and/or notes limiting a datum to a perimeter around the hole pattern (if flat, but flexible) could be required.

Peter Truitt
Minnesota

 

[KENAT]

Does the standard need to be simpler, or does the training and certification environment need adjusting?

I've long wondered if there should be another lower level of GD&T certification, not one that focuses on esoteric aspects or trick questions... but one that covers the typical day to day basics.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[ptruitt]

Jim,

Do you think that my example would be a problem for shops mainly due to a lack of the tools needed to inspect parts or mainly due to their lack of understanding of the profile callouts?

Ken,

My last week of GD&T training (2010) pushed profile tolerancing very hard. Some of the students were in college and barely even had blueprint reading skills. By the end of the training, they seemed to fully comprehend composite profile applications with and without datum structures. So it seems to me that some of the other methods, such as 0 (M), get in the way of what seems to me to be a better, comprehensive way to bring new students up to speed.

Peter Truitt
Minnesota

 

[MechNorth]

Peter,
The problem is composite of both issues. What I've seen too often is that shop doesn't have the ability / knowledge to check a profile tolerance because they have never been trained adequately, or more specifically because some instructor told them it requires a big expensive CMM. I've taught people how to do open setup inspections for exactly this sort of thing without issue. Also taught them how to do it with a CMM, with an optical comparator, with a vision system, ... you get the idea.

I find that college/university students seem to accept the material easily enough, but few understand what it means in the "real world" of metal, plastic, etc. Another example of "theory is great, but what what do I do with it".

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[powerhound]

Jim,
A few posts back you mentioned that if you specify a tolerance on a drawing then you should be able to measure it. Are you saying that legally, as in court, it is incumbent upon the customer to prove that a part is NOT to spec as opposed to the supplier proving that a part IS to spec?

If that's the case then some people here where I work are really going to have to re-evaluate how they spec parts. These guys regularly tolerance parts to values that we cannot verify such as a cylindricity tolerance of .001 mm.

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[ptruitt]

Maybe. A prosecuting attorney may show you a drawing and ask you what the drawing means and how you verified that the product met the spec's. If Jim is working for the prosecuting attorney, you may be in trouble. You might show why the need to meet it is not relevant, but you might still look incompetent and compromise the outcome. Of course, 0 (M) is not the same as +/- zero, but you would need Frank to stand up to Jim. I think that .001 mm cylindricity would not look good in court unless your measurement uncertainty and bias compensation are accurate and reproducible...

Peter Truitt
Minnesota

 

[MechNorth]

Interesting question, Powerhound. If I understand the judicial process correctly, the claimant (customer, assuming they are suing over bad parts; supplier if they are suing for payment for parts) would have to establish that they have a legitimate case as a first step. A situation of point/counter-point, I think. So, if the customer is suing, then they'd have to prove that the parts don't meet their spec. If the supplier is suing, then they'd have to prove that they do meet spec.

As Peter indicates, it's GDTP-S's & P.Eng's (P.E.'s)that tend to be called as expert witnesses to determine the meaning of the print and whether or not something is inspectable by nature of the geometries, materials, and whatever other factors.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[ptruitt]

In a liability case, be prepared to defend the drawing, design, traceability, and quality of fabrication.

Peter Truitt
Minnesota