Tolerance for Valve seat

[BlueV]

Hi,
Im new to GD&T and getting to grips with the usage and understanding. So I was going through this Link . Here (page 14) it says valve seat is controlled using circularity and cylindricity.

Why not use total runout ?

Thanks and Regards,
Blue_V

 

[CheckerHater]

Blue,
First, It is generally agreed that total runout is well defined for cylindrical surfaces and not so well for conical, giving ways for misinterpretations (one may argue about that).
Second, on the page 14 it says VALVE GUIDE and not the valve seat is controlled by cylindricity.
And third, the authors of the brochure say that "Traditional measuring means are not sufficient to precisely control valve seats and valve guides" because they are trying to sell the machine to measure just so: "circularity, concentricity, run out, cylindricity, segment linearity, angles, surface finish..." Fair enough?

 

[BlueV]

Sorry, not valve seat obviosly. Thanks for the reply. Do you know of any links for practical applications of geometrical tolerances with examples?

 

[CheckerHater]

Your question is larger than life obviously.

The best sources are paid-for sites like this:

http://www.draftingzone.com/

Some may offer a bit of basic knowledge for free, like this one:

http://www.etinews.com/gdt_glossary.html

This place:

http://www.tec-ease.com/gdt-terms.php

used to be free but now offers premium services (premium is not so high though).

This place:

http://www.mechsigma.com/

offers some free insight, but was not updated for years and based on 1994 standard. Click "Newsletters" button.

And there always are books in your local library.

Good luck!