GD&T

[Jacoolo]

well in general, one can ask - what for use GTOL when tolerance for dims exist?

When You will answer this question You will know what the GTOL is.

Interested?

So - in big assumption - GTOL comes to the scene when replace ability is needed in your parts or assemblies. It plays much more role when same parts are delivered by different suppliers. It can occur that all of parts have right tolerance and dims but they do not fit each other. Why one can ask? Because dims do not say anything about the shape of surfs - i.e you can have shaft and whole with proper dia but they do not fit. It is like that because the dia is ok, but the surf for whole and shaft are not parallel. You can not establish this by dims but You can and You should make it by GTOL.

So when You make i.e valves with rods, o-rings, covers, etc, and you want to be sure that they always will fit each other, put expected GTOL on valid surfs.

 

[sanjeevkar1]

i have got something for jelston


http://www.tec-ease.com/tips/july-02.htm

 

[Jacoolo]

these are my tow eurocents to the "links" topic

http://www.roymech.co.uk/Useful_Tables/Drawing/draw_geom.htm l

 

[jelston]

 

[blumb]

Hi Jelston.


The book Ikeep referring tois from Paul Drake called "Dimensioning and Tolerancing Handbook" ISBN 0-07-018131-4.


[url]http://www.amazon.com/Dimensioning-Tolerancing-Handbook-Paul -Drake/dp/0070181314/ref=pd_bbs_sr_2/104-6163695-1707130?ie= UTF8&s=books&qid=1183041877&sr=1-2 [/url]
The book is in-depth, formal, comprehensive, and an advancedreference manual for understanding GD&T. As a long time student and practitioner of GD&T I use the book to verify my thoughts and to refresh my knowledge on the subject.


Hope this helps.

 

[SrGilberto]

I think the origninal question is: When to use GD&T and when not to. I used to teach GD&T and where I work now I almost never use it, although ocassionally I advise people here on how to apply it.


I now work in R&D and so what I design and build are prototypes and therefore GD&T is not necessary. One great usefulness of GD&T is to be able to repeatably produce acceptable parts with fewer scrap parts. So... having said that, GD&T is great for production parts but my prototype parts can simply have linear dimensions and tolerances as I'm just trying to prove a design concept.


Also remember this: machine shops don't usually build a part according to the GD&T. They will produce the part as accurately as they can. The GD&T is a great tool for inspectors to verify that a part will fit properly.


Also, repeatability and consistent conformityof parts is a real great benefit for GD&T (along with fewer scrap parts).


Best Regards,


SrGilberto