How to determint the value of GD&T for different manufacturing processes?

Look up "ANSI Y14.5" on the web.

thanks for the reply,

but my actual question is that is how can we determine tha value of the tolerence of the different features like parallism,cylidricity,concentricity etc of GD&T for different machining processes like grinding,planning,milling etc.?

If any one can explain giving the practical example I would be more thankful.

GD&T is a function of "fit" and/or function. Generally, the difference in size between the mating parts determines how far "off" their respective positions from a "basic" (perfect) location can be. As far as parallelism, cylindricity, perpendicularity, etc. is concerned these are also a matter of function. The function of the part will determine how "tight" these tolerances should be. I strongly suggest you visit the ANSI Y14.5 web site or aquire the book. Mr. Lowell Foster is pretty much the 'Guru' of GD&T and, for the most part, author of "Geometric Dimensioning and Tolerancing" which is the title of the book you must read. In this book all of your questions are addressed, explained and shown how to properly implement them on your drawings so as to correctly produce the required finished product. There is no real "Rule of Thumb". One must take into consideration the function of the item and its assembly with mating parts when determining tolerancing of its dimensions. Is the part/assembly dynamic?(Does it rotate or perform a linear motion function?). Is heat a factor?(will the item(s) expand or contract,etc.) There are many questions that need to be answered before one can realisticly tolerance the items for production.

thank u vry much for the explanation

ya it is obvious that the tolerance depends upon the functionality of the components, but if we have to assign the value of the tolerance for the part that is machined by the perticular process e.g. like planning machine then what would be the range for the tolerance vaules of different features? Is it only depends on the cpk value or else we can find out by any other method?

if u know some practical examples regarding the above question ,please give so it would be easy to understand.

And i refer the tarining program for GD&T by TCI,Al Neumann,

The question you have posed seems a little like putting a cart in front of the horse.

When an article is designed, the necessary clearances and levels of "fit" are determined by the design. Parallelism, runout, flatness and so on are design factors to be supported by the end process.

Once the design requirements are specified

THEN

You look for a supplier who can satisfy those criteria with the equipment and processes that they have at hand. (I'm talking about demonstrated capability.)

The reason to look at demonstrated capability is that two suppliers may have similar equipment, but one may be well maintained and the other poorly maintained and worn out. You need to find the one that can satisfy your tolerances.

For instance, our own toolroom has three lathes. They each have different capabilities (due to age, quality of machine and levels of maintenance performed over their life) so there is no single "magic number" for the ability of a lathe to satisfy GD&T expectations.

As suggested by previous, read the various texts and standards that are out there.

And by the way, welcome to this forum. Don't be shy in asking questions.