To GD&T or not to GD&T ??? 2

[dtmbiz]

This forum is a curiosity to me. Over the years it seems as if there are a number of comments that indicate the use of GD&T is only for certain situations . Besides the forum I have encountered many who believe that if the design involves; a “simple part, or a “one off”, or precision tolerances are not required; then GD&T (ASME Y14.5) shouldn’t be used or isn’t necessary; too confusing to manufacturers and/or too time consuming.

Personally, I recommend that it should be used on all components; simple or complex, loose or tight tolerances, prototypes,” one of a kind”, production or whatever the situation.

I have been taught over the years that it is a language which uses a set of symbols, rules and concepts to communicate design function and assembly interfaces by accounting for and applying all geometric characteristic requirements to features and by showing feature relationships to each other and feature datum’s; and allowing inspection to receive more parts that do function, along with costs savings.

Wondering how many forum members are advocates with successful experiences by applying GD&T or if the numbers lean toward the camp who actually don’t really see its value, but are more or less forced to use it?

Not sure if the majority of forum members value the standard or if it is just a nuisance that needs to be dealt with at times?

Yea or nay for GD&T?

 

[ewh]

I'm in the camp that feels it should be used on all components but am limited by the culture of my current workplace. So I'm fighting it one battle at a time.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[TheTick]

Low-skill, low-cost vendors do not like GD&T, since it is difficult to understand and expensive to implement. It is not uncommon for such vendors to charge more for parts with GD&T on the drawings.

 

[swertel]

When applied properly, GD&T can actually reduce the cost of a part. But so few people are familiar with the nomenclature that when they see a feature control frame, they automatically double the cost of the part.

--Scott
www.wertel.pro

 

[JNieman]

I agree with your philosophy. In an ideal world, you're right.

In this world, however, you accommodate the natural forces at work. If your part can be sent out to any John, Dick, or Tom, with a band saw, then make it easier to read. In the USA, it seems, Feature-Control-Frames are only taught in a 'specialty' class, in my experience, though that may have changed in recent history. Machinists are taught that if they go to some manner of trade or post-secondary school. If they go through an apprenticeship, they may never get that education. Some owners will see the use of "GD&T" as a sign that the customer may require more paperwork, more documentation, and be more stringent in their inspection, or have more "overhead work" that keeps them from cutting chips, which is where their money is made. There is more to the price of the part than simply whether or not you allow a .03 square tolerance zone, or a .042 diametric tolerance zone for hole locations. Also note that some think "true position" requires a CMM to inspect, or requires them to sit down and do some math work. So, HOW you call things out can sometimes influence what tools are required to inspect - further limiting your supplier pool, possibly.

In short... if you keep a print dumbed down, you might get quotes from cheaper suppliers rather than a "No Quote" from them, or an inflated price.

I can sympathize with both sides of the conversation.

_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5

 

[MikeHalloran]

I was introduced to GD&T at Ford Motor Company, in 1967.
The company paid for on-site training, of _everyone_ involved in the design, prototyping, inspection, inspection, and tooling processes. ... including secretaries and purchasing agents. ... in short anyone who might ever see a blueprint was invited and paid to attend.
I think that the GD&T rollout goes a lot better if everyone has some exposure to it before drawings with odd symbols start to appear.

At other outfits with less enlightened management, I have done the one battle at a time thing, by borrowing pieces of GD&T symbology and using them for their clarity. For example, it's pretty easy to explain to someone that the slanted arrow for runout is exactly analogous to a dial indicator, or that a vertical arrow in text means depth. I leave the 'bonus tolerance' stuff for pedantics; it's too complicated to explain in a minute or two, and it is very rarely applied correctly anyway.

As for pricing, yes, a shop that hasn't invested in training is likely to overbid, but maybe you don't want to deal with that shop anyway, unless you like spending a lot of time on the phone explaining what you really wanted.



Mike Halloran
Pembroke Pines, FL, USA

 

[ctopher]

It should be on all part drawings.
Unfortunately I see more parts being machined overseas, or cheap shops in the USA, that don't understand or follow GD&T.
The goal these days is to reduce price. One way is to remove GD&T from the drawings. It's backwards IMO.

Chris, CSWA
SolidWorks '15
SolidWorks Legion

 

[CheckerHater]

I do believe that we need "a language which uses a set of symbols, rules and concepts to communicate design function and assembly interfaces by accounting for and applying all geometric characteristic requirements to features and by showing feature relationships to each other and feature datum’s; and allowing inspection to receive more parts that do function"

I also believe that it hasn't been created yet.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[KENAT]

I generally make fairly full use of GD&T though I will avoid some of the more esoteric options.

thread1103-192933

Posting guidelines faq731-376

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

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

 

[dgallup]

I'm certainly not of the camp that thinks everything should be fully dimensioned in GD&T. For instance, I never use basic dimensions for the outline of a part and give it an overall profile tolerance. I like to dimension features of size so they can be inspected with a simple caliper or micrometer. On the other hand, where it is appropriate for the function of the part I make extensive use of true position, flatness, straightness, profile, etc. I've only had one case in recent memory of a vendor fighting over a GD&T symbol and they were German, not some low cost 3rd world supplier.

Paradoxically, when I need something highly precise made in our tool shop I tend to give them very little in the way of any kind of tolerances. Those guys are highly skilled machinists with tremendous experience and I just sketch something out and explain how it should work and I get back a piece of art. But those are one off items that won't be repeated and there is no purchasing or quality department involved.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[Belanger]

Keep in mind that a drawing is a legal document. So for those who say GD&T might not be needed on a simple part, I could explain a situation where their print is ambiguous (think datums) and thus they may be on the hook for thousands of dollars' worth of scrap/rework after the case is hauled through a courtroom or arbitrator.
Now ask them again if they want to take that gamble.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[axym]

dtmbiz,

I'm not sure what kind of answers you were expecting with this question. It's kind of like asking whether or not CNC machining should be used to make parts, or whether or not 3D CAD should be used to design them. There isn't a simple yes or no answer.

Having seen many GD&T successes as well as many failures, I would say that it should not be used on all drawings. There are many situations in which GD&T does not add value over plus/minus tolerancing. I often say in my classes that bad GD&T can be much worse than none at all.

If specified in accordance with the standards, the meaning of GD&T specifications will be more well-defined than plus/minus specifications. But there is more to it than that. If the design function has not been analyzed or defined, the assembly interfaces are not utilized, if the geometric requirements and feature relationships have not been researched, if the drawing tolerances are never fully inspected and verified, then the costs associated with the GD&T drawing can outweigh the benefits. The others have brought up other reasons, and there are many more.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[dtmbiz]

Thank you all for taking your time to answer.

It is actually a yes or no question.

Not surprised at the response ratio; just affirmed my experiences.

I was not trying to reconsider my view just an assessment of the forum site.

I have noticed over time that many responses to answer a GDT question wind
up going down the path of “don’t use it”.

If I go to a chess club to play chess, I don’t actually want to have a substantial number
the members tell me not to bother with chess, checkers is simpler and more widely accepted.

I am okay with the opinions from the forum, everybody has them.

Thank you again for your sincere responses!

 

[CheckerHater]

I hope you are sincere comparing GD&T with chess.

More like D & D - too many rule-books.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[KENAT]

dtmbiz - off topic but...

Any reason you'd decided to post all in bold lately? Comes across as, let's say a little 'assertive'.

Posting guidelines faq731-376

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

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

 

[dtmbiz]

Kenat,

Not trying to be assertive, simply helps me see better

maybe we could be a little more empathetic with those that dont have 20/20.

Do it for emails, and Word processng too.. and I like it

 

[ewh]

I have to admit, it is easier to read and not as assertive as if also all caps.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[KENAT]

Fair enough.

Posting guidelines faq731-376

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

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

 

[ctopher]

My optometrist uses all caps, and I still can't see it!


Chris, CSWA
SolidWorks '15
SolidWorks Legion

 

[axym]

So should I use bold font when I type something on the computer, or should I not use it? Simple yes or no answer please. ;^)

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca