Profile and MMC
Profile and MMC
(OP)
Would it be acceptable to have the profile of a surface as "zero" at MMC?
Then as the size devates from the MMC the profile tolerance would increase.
Then as the size devates from the MMC the profile tolerance would increase.





RE: Profile and MMC
In a copy of the standard or your textbook, look up unilateral profile tolerances. You do not call up MMC, but you accomplish the same thing.
RE: Profile and MMC
M can be only applied to feature-of-size elements while profile of surface as it is called controls surfaces only.
However M can be put in a datum portion of profile of surface feature control frame as long as referenced datum feature is a feature-of-size.
RE: Profile and MMC
RE: Profile and MMC
RE: Profile and MMC
Also, in Y14.5'09, a surface (planar, or irregular boundary) can now be used as a datum feature, and the resulting datum can be referenced in a drf at MMC. Of course, the tolerance within the profile fcf still cannot have an MMC or LMC modifier There are some good figures in the book.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Profile and MMC
Where does specifying a surface profile tolerance without a DRF leave us in terms of inspection of a complex surface?
Also is this explicitly stated somewhere in the '94 version of the standard? I'm on my 20+ time perusing section 6 and I only see section 6.5.6.1, Fig 6-20, & 6-21 where a surface profile without a DRF is applied to planer surfaces (similar to how a flatness tolerance my be applied).
I'm also aware of no DRFs being specified in the 2009 version when it comes to composite profile and combined tolerances, but I'm getting ahead of myself.
RE: Profile and MMC
Getting to the use without DRF is an exercise. 6.5.1 says that it is used to control form or combinations of size, form, location and orientation. Form is not related to datums, therefore in the absence of a drf, all you get is form ... the next extension then is to recognize that "form" for an enclosed boundary is essentially a size control as well. 6.5.4 Indicates that in most cases, Profile requires a drf. (i.e. not always required).
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Profile and MMC
RE: Profile and MMC
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Profile and MMC
RE: Profile and MMC
I believe I know the fellow in Minnesota that taught your class. He certainly does have some strong opinions about profile.
It's true that many characteristics in Y14.5 can be thought of as special cases of profile. The tolerance zones for flatness, perpendicularity/parallelism/angularity of a planar surface, cylindricity, and total runout can be duplicated using permutations of surface profile.
Some people find the idea of a reduced set of characteristics to be simpler, others find it more complicated.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: Profile and MMC
I like profile tolerances a lot, however, your comment is extremely general. We would have to write out some problems, and see how everybody would solve them.
RE: Profile and MMC
As Evan indicated, many of us on this forum will know the instructor you indicate. He presents some very interesting questions about profile in particular that are glossed over in the committee and standards so far. As more people and companies evolve in their use of profile, things change and improve wrt the definition of the control.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Profile and MMC
RE: Profile and MMC
I suppose that you could replace all of the Flatness and Perpendicularity symbols with Surface Profile and achieve the same tolerance zones and constraint behaviors. I'm not saying that I recommend doing that, but you could.
There are other characteristics that can be converted into a variant of Surface Profile, but it gets more complicated. Parallelism and Angularity for planar surfaces can be expressed as Surface Profile, but you need to make sure to relieve the location constraint. This can be achieved by using a composite FCF (the lower tier only orients the tolerance zone to the DRF and does not locate it) or by combining the Surface Profile FCF with a plus/minus tolerance.
It is also possible to express Cylindricity or Total Runout as variants of Surface Profile, but this is even more obscure and controversial. The Surface Profile FCF must be combined with a plus/minus tolerance.
When characteristics are "simplified" into variants of Profile, the drawing reader must have a much deeper understanding of degree of freedom constraint concepts to derive the proper meanings.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: Profile and MMC
Your design requirements.
I have frequently done a composite FCF with a profile tolerance and either a parallel, perpendularity or angle specification. Typically, the profile tolerance is sloppy. The second feature is what I am really concerned with.
Don't forget that the profile controls more stuff than flatness and perpendicularity. The whole point of GD&T is to control the stuff you need, and to not control the stuff you do not need.
RE: Profile and MMC
Combining Profile with another characteristic is a great idea, that allows the largest functional tolerances. I hate to be the terminology police but that's never stopped me before ;^). If you combine a Profile FCF with a Perpendicularity, Parallelism or Angularity FCF, then it's called a multiple single segment FCF. Not a composite FCF.
You're right that Profile is capable of controlling more than just the form (e.g. Flatness) and orientation (e.g. Perpendicularity) of a planar surface. It is also uniquely capable of controlling the location of the surface. But things can be manipulated to make Profile control form only or form and orientation only. If no datum features are referenced, then Profile will control form (Flatness) only. If the only datum feature referenced is nominally square to the considered feature, then Profile will control form and orientation only (Flatness and Perpendicularity).
Again, I don't recommend replacing Flatness and Perpendicularity callouts with Profile, just because we can.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca