Some Question about GD&T
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Posted by: black16941 ® 09/20/2006, 12:00:10 Author Profile eMail author Edit

Dear all: I read some books about GD&T Any disadvantage of this method existing? Thank you

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Re: Some Question about GD&T
Re: Some Question about GD&T -- black16941	Post Reply	Top of thread	Forum

Posted by: Kelly Bramble ® 11/14/2006, 08:20:27 Author Profile eMail author Edit

See /training_engineering/advantages_geometric_dimensioning_tolerance.htm and /What_Is_GD&T.htm Modified by Kelly Bramble at Tue, Nov 14, 2006, 08:21:01

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Re: Some Question about GD&T
Re: Some Question about GD&T -- black16941	Post Reply	Top of thread	Forum

Posted by: sunnyputu12 ® 11/14/2006, 02:08:40 Author Profile eMail author Edit

I have never come across any dis-advantages . As far as part costs are concerned , GD&T when properly used , ensures low rejection rate . After functionally analysing the parts in an assembly , we give tolerances and GD&T to the part dimensions . This is absolutely necessary to ensure a good result from the assembly

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Re: Some Question about GD&T
Re: Some Question about GD&T -- black16941	Post Reply	Top of thread	Forum

Posted by: Kelly Bramble ® 09/20/2006, 12:09:08 Author Profile eMail author Edit

The only disadvantage I am aware of is the perception of GD&T. I have used and trained GD&T classes for many years. The advantages are too numerous to list within this forum thread. Unfortuantly, many talented designers and engineers whom have not been trained in GD&T techniques tend to have mis-conceptions.. Modified by Kelly Bramble at Wed, Sep 20, 2006, 12:10:31

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Re: Re: Some Question about GD&T
Re: Re: Some Question about GD&T -- Kelly Bramble	Post Reply	Top of thread	Forum

Posted by: black16941 ® 09/20/2006, 22:29:57 Author Profile eMail author Edit

Kelly: Thank you! In fact, I am student living in Taiwan, not engineer. I found some books about ASME Y14.5M in library. Many difference between ASME and CNS dragting stadard. CNS drafting standard, used the reference resource from ASME drafting standard, but many concepts had be canceled Such as Virtual condition, Resultant condition, Pattern-locating tolerance zone framework, Feature-relating tolerance zone framework...etc. I am interesting in GD&T training course. In Taiwan,where is the GD&T training??

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Re: Re: Re: Some Question about GD&T
Re: Re: Re: Some Question about GD&T -- black16941	Post Reply	Top of thread	Forum

Posted by: Kelly Bramble ® Administrator, Administrator 09/21/2006, 08:15:58 Author Profile eMail author Edit

I do not know of any training medians in Taiwan. I can only suggest that you contact any designers or engineers you know and ask them. You should also try your local college or university system. Good luck!

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Re: Re: Re: Re: Some Question about GD&T
Re: Re: Re: Re: Some Question about GD&T -- Kelly Bramble	Post Reply	Top of thread	Forum

Posted by: traingdt ® 09/21/2006, 11:50:41 Author Profile eMail author Edit

Yes, as Kelly said, the disadvantage is the lack of knowledge by many people, both in the actual design and also downstream in the process. Two examples: Some people say that GD&T increases the cost of a part. Not true -- the characteristics that GD&T addresses (size, shape, position, etc.) had to be checked anyway, and may have merely been implied. The GD&T just uses a standardized method to address them clearly. Another example of lack of knowledge is a designer applying something like concentricity without understanding the full meaning of that symbol. Concentricity is nice in theory, but it is difficult to measure and should usually be replaced with position or runout. Hope that helps, John-Paul Belanger

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Re: Re: Re: Re: Re: Some Question about GD&T
Re: Re: Re: Re: Re: Some Question about GD&T -- traingdt	Post Reply	Top of thread	Forum

Posted by: Kelly Bramble ® Administrator 09/21/2006, 12:35:54 Author Profile eMail author Edit

John-Paul, Lately, I have been in several classes where an engineer/designer said that they "know" that using GD&T will get a higher quote from manufacturers. I allways ask if I can see the specific drawings they are reffering to. So far, nobody has produced any drawings and associated quotes. Have you seen any such examples?

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Re: Re: Re: Re: Re: Re: Some Question about GD&T
Re: Re: Re: Re: Re: Re: Some Question about GD&T -- Kelly Bramble	Post Reply	Top of thread	Forum

Posted by: scalarcharge ® 10/04/2006, 12:35:38 Author Profile eMail author Edit

I was taught to use GD&T in school, but once on the job I abandoned it. All quotes were higher with GD&T. The only reason I can think of is lack of familiarity. When my professor toured a local workshop and asked how often they had prints using GD&T and how they handled them, the machinist said, "Ahh, we just know to be reeaal careful when we see those." I'm betting that the callouts are just interpreted as tighter tollerances or they just work at tighter tollerances to cover all their bases.

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Re: Re: Re: Re: Re: Re: Some Question about GD&T
Re: Re: Re: Re: Re: Re: Some Question about GD&T -- Kelly Bramble	Post Reply	Top of thread	Forum

Posted by: black16941 ® 09/21/2006, 22:42:22 Author Profile eMail author Edit

Thanks for you reply As John-Paul said, I think the positonal tolerance can be used to control symmtrical relationship and coaxiality. The concepts of symmtry and concerntricity different from potional tolerance, symmtry and concerntricity use the median point, I don't know the suitable time for choosing location tolerance. I found many problem when I read these books. Maybe, I need experience to distinguish these concept, reading is not enough. Next week, I will participate in Geometracal Tolerancing course about CNS. I will share my experience to you. But, it may let people down. Thank you.

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Re: Re: Re: Re: Re: Re: Re: Some Question about GD&T
Re: Re: Re: Re: Re: Re: Re: Some Question about GD&T -- black16941	Post Reply	Top of thread	Forum

Posted by: traingdt ® 09/21/2006, 23:36:59 Author Profile eMail author Edit

I too have heard those stories, Kelly. One fellow said he used to work with a manufacturer that basically took their baseline price quote for a similar part, and then multiplied it by a certain factor for each GD&T callout on the customer's print! I don't know if that's really true -- but I tell designers/engineers that if your suppliers are jacking up the price because you have used GD&T, then they don't understand today's manufacturing standards and you might want to shop around.

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Re: Re: Re: Re: Re: Re: Re: Re: Some Question about GD&T
Re: Re: Re: Re: Re: Re: Re: Re: Some Question about GD&T -- traingdt	Post Reply	Top of thread	Forum

Posted by: black16941 ® 09/22/2006, 01:25:28 Author Profile eMail author Edit

I have a question from your reply. In my mind, the GD&T method should be universal in your engineering field. But your reply message appears some manufacturer doesn't use GD&T.

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Re: Re: Re: Re: Re: Re: Re: Re: Re: Some Question about GD&T
Re: Re: Re: Re: Re: Re: Re: Re: Re: Some Question about GD&T -- black16941	Post Reply	Top of thread	Forum

Posted by: rjbeng ® 09/22/2006, 22:59:08 Author Profile eMail author Edit

As an engineer and a manufacturer I have seen both sides of the issue and feel that if done correctly GD&T will reduce costs and provide the customer with a more consistent part. Now, if it used incorrectly your costs will go up. The key to GD&T, is ask and inspect to what you need. This way your supplier knows the keys to hit and the rest will follow without driving up cost. Another consideration is the supplier base that does not understand GD&T. They will jack the price just because they see more numbers than they are use to. I have seen a simple machined part with plenty of room, +/- .030, come back with a differential cost of 500%. After talking to the supplier, it became very apparent that they did not know how to read the GD&T call outs. Another point to keep in mind is, know your audience and help them as required to understand the benefits of GD&T. As a final note, if you are looking for a book to help you along. See Geometric Boundaries, Interpretation and Application of Geometric Dimensioning and Tolerancing by Kelly L. Bramble. I have used this to enlighten drafters, designers and engineers to the benefits of GD&T. Sorry Kelly, I had to do it.

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Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Some Question about GD&T
Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Some Question about GD&T -- rjbeng	Post Reply	Top of thread	Forum

Posted by: ravindraspatil1 ® 10/04/2006, 01:26:28 Author Profile eMail author Edit

how to get that book ?? price ?

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Some Question about GD&T
Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Some Question about GD&T -- ravindraspatil1	Post Reply	Top of thread	Forum

Posted by: harshad_friend ® 03/31/2007, 09:44:28 Author Profile eMail author Edit

Dear all, can anybody explain me the meaning of MMC(Max. matl. condition),LMC(Least matl. cond.) & RFS(Regardless of Feature Size) in the context of GD & T? i feel, i'm in the right thread with right people. thanx by n tc

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Some Question about GD&T
Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Some Question about GD&T -- ravindraspatil1	Post Reply	Top of thread	Forum

Posted by: harshad_friend ® 03/31/2007, 09:42:58 Author Profile eMail author Edit

Dear all, can anybody tell me what exactly the meaning of MMC,LMC & RFS in the context of GD & T? i feel, i'm in the right thread with right people.

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