Eric,

You are correct on both counts.  There are numerous tolerancing
specifications.  A well documented print will state which tolerancing
specification was used.  Since I am located in North America, it is the
ANSI specification that I see called out the most.

There is quite a bit of confusion about geometric tolerancing -- it is
not as easy to understand as bilateral tolerancing.

Jay Soderberg

Here goes the opinion thing:  They are mine and mine alone.  Others may
reasonably disagree.  These opinions do not necessarily reflect the
opinion of the ownership or management of this establishment.


>    ----------------------------------------------------------------
>
> Subject: Re: TechNet Digest - 3 Jun 1999 - Special issue
> Date: Fri, 4 Jun 1999 07:16:32 -0500
> From: Eric Christison <[log in to unmask]>
> > Adeline,
> >
> > True position can be defined as the exact location of a feature as
> > defined on the print (or some other manner) without taking any
> > tolerances into account.  A bilateral tolerance expresses the
> maximum
> > allowed variation as dimension based on an X-Y coordinate system.
> > Geometric tolerancing expresses the tolerance as zone of allowed
> > variation based on a circle of a defined diameter centered at the
> true
> > position.  The diameter expresses the allowed variation.
> >
> > As Tom Burek pointed out, there are a number of variations possible
> when
> > using geometric tolerancing.  Tom mentioned MMC (maximum material
> > condition), but there are others also (LMC - least material
> condition,
> > RFS - regardless of feature size both come to mind).  These
> additional
> > call outs change how the tolerance is applied.
> >
> > A good reference for all types of dimensioning is the publication
> ANSI
> > Y14.5M, Dimensioning and Tolerancing.
> >
> > Jay Soderberg
>
>
> If you are working outside North America or dealing with customers
> outside
> North America you should refer to the ISO standard whose ref. number I
> have
> forgotten. However, if you are based in the UK refer to BS308 which is
> compatible with the ISO spec and is an excellent document.
>
> It's important not to assume that ANSI drawing and tolerancing
> definitions are
> the same as ISO.
>
> However, if you're ever in any doubt it's best to ask the originator
> of the
> drawing. Twenty years of misunderstandings has taught me that many
> people
> (including those who use it) don't really understand this method of
> tolerancing. That's why I, for one, don't use this method unless I
> really have
> to.
>
> Regards,
>
>
>
>
>
> Eric Christison
>