To GD&T or not to GD&T ???
To GD&T or not to GD&T ???
(OP)
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?





RE: To GD&T or not to GD&T ???
"Know the rules well, so you can break them effectively."
-Dalai Lama XIV
RE: To GD&T or not to GD&T ???
RE: To GD&T or not to GD&T ???
--Scott
www.wertel.pro
RE: To GD&T or not to GD&T ???
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
RE: To GD&T or not to GD&T ???
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
RE: To GD&T or not to GD&T ???
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
RE: To GD&T or not to GD&T ???
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
RE: To GD&T or not to GD&T ???
thread1103-192933: GD&T part costing more
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: To GD&T or not to GD&T ???
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.
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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.
RE: To GD&T or not to GD&T ???
Now ask them again if they want to take that gamble.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: To GD&T or not to GD&T ???
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.
www.axymetrix.ca
RE: To GD&T or not to GD&T ???
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!
RE: To GD&T or not to GD&T ???
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
RE: To GD&T or not to GD&T ???
Any reason you'd decided to post all in bold lately? Comes across as, let's say a little 'assertive'.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: To GD&T or not to GD&T ???
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
RE: To GD&T or not to GD&T ???
"Know the rules well, so you can break them effectively."
-Dalai Lama XIV
RE: To GD&T or not to GD&T ???
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: To GD&T or not to GD&T ???
Chris, CSWA
SolidWorks '15
SolidWorks Legion
RE: To GD&T or not to GD&T ???
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: To GD&T or not to GD&T ???
_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: To GD&T or not to GD&T ???
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: To GD&T or not to GD&T ???
Chris, CSWA
SolidWorks '15
ctophers home
SolidWorks Legion
RE: To GD&T or not to GD&T ???
FOR THE MERCILESS, NO MERCY
I ACTUALLY THINK THERE ARE LAWS AGAINST YOU GUYS.
FEDERALLY PROTECTED SPECIES
WHINERS
RE: To GD&T or not to GD&T ???
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: To GD&T or not to GD&T ???
got it
but its realyly reallly reali is hard givin up assertivness... exspshially when i
dident evan noe it
RE: To GD&T or not to GD&T ???
Chris, CSWA
SolidWorks '15
ctophers home
SolidWorks Legion
RE: To GD&T or not to GD&T ???
D&T is also about communicating with people - also not a game. And those people may not be well versed in it or see no need for the language choice.
My take is that ASME is driving away from popular adoption in the most effective way possible. The cost of the standard is high, there are errors in the current version that should not have made it past a good editor, the latest version adds significant complexity without also increasing the clarity of explanation, and their certification program is ridiculously expensive. It should be tough and it should be cheap. And it should emphasize outcomes and not vocabulary. It doesn't matter if its a Least Material Boundary - it does matter what the wall thickness might be.
The main ASME failing is not pursuing an inexpensive, unbiased algorithmic program that can provide evaluation of tolerances and the resulting likely variations. With this in place users of the standard at any point in the product chain could evaluate the effect of tolerance choices* in an unambiguous way even if they don't know how to interpret the expected outcomes**. However, some of these programs have been made available by other parties and industry has generally decided that they are doing just fine without quantifiable feedback on the ability of the product chain to control variation in finished products.
*For example, manufacturing should be able to see how their fixturing deviations affect the final part.
**How many can, by hand, calculate the natural log of a number or even know how, yet can press the ln button on the calculator? Why should D&T be any harder to evaluate?
RE: To GD&T or not to GD&T ???
ti wereked,
It worked (see what I mean)
btw
observations demonstrated and this mind set is not uncommon IMO,
such disdain for the the ASME Y14.5 standard? yet you participate in the forum?
what is the draw for you?
RE: To GD&T or not to GD&T ???
So far, in the world of GD&T, one has to hire Certified Road Sign Professional every time one takes car out for a spin.
That's the reason lot of people prefer to walk or stay home (figuratively speaking)
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: To GD&T or not to GD&T ???
Funny CH
splains alot...
RE: To GD&T or not to GD&T ???
I can like a subject and dislike it being handled poorly, both at the same time.
RE: To GD&T or not to GD&T ???
_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: To GD&T or not to GD&T ???
But I always worry a lot when doing it. I work in a weak manufacturing town of a weak manufacturing state of a weak manufacturing country. There is relatively little exposure to what everything means here. But people won't always admit it if they don't know. It's a very difficult topic to breach without making yourself look like an elitist.
By way of example, our company is a production line that probably has around 40-80 floor staff depending on market conditions. Amongst them are 10-20 qualified machinists/fitter turners/toolmakers etc. The most experienced amongst those, when asked if he knew what to do with a print with GD&T tolerances on it, said "Oh I've seen that before, those are what you find on really rough stuff like castings".
RE: To GD&T or not to GD&T ???
You are lucky, in a way, in that your machinists are merely ignorant, and therefore trainable.
I have faced a too-experienced drafting supervisor who really thought he understood GD&T, but clearly did not understand statistical tolerancing, or much else. Under his iron fist, his department came up with a piece of tooling plate that was 'located' with ~28 holes for a corresponding number of machine screws. In order to satisfy his understanding of geometric tolerancing, the clearance holes on the screws were bigger than the biggest dimension of a pan head, and hence field technicians had to be equipped with fixtures to locate the plate, which was R&R'd frequently, and of course if it was located correctly, you couldn't tighten any of the screws, and the plate would lift right off, if you forgot the fender washers.
You can't fix stupid.
Mike Halloran
Pembroke Pines, FL, USA
RE: To GD&T or not to GD&T ???