PERFECT ORIENTATION AT MMC NOTE

[ringman]

I am curently checking drawings prepared in accordance with ASME Y14.5-1994. The first note on the format states 'DIMENSIONING AND TOLERANCING IN ACCORDANCE WITH ASME Y14.5M-1994.' and as a part of that note, 'UNLESS SEPARATE TOLERANCES ARE SHOWN, PERFECT ORIENTATION AT MMC FOR RELATED FEATURES IS REQUIRED. GENERAL ANGULAR TOLERANCE DOES NOT APPLY TO IMPLIED 90 DEGREE ANGLES.'

These notes are to be a part of the format and do not consider Coaxiality, nor Symmetry.

My questions are: Are there others who impose this note on the format and is it a consensus that it is any value added to the part definition?
and
Would not this be covered by Rule #1 by default?

 

[ringman]

Kindly disregard the last question, 'Would ot.....default?'
please.

 

[ctopher]

I think most production people will not understand those notes. It is not a common not. I would reword it.

Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 06/08
ctopher's home (updated Apr 30, 2008)

 

[drawoh]

ctopher,

Heck, I don't understand that note.

...PERFECT ORIENTATION ... IS REQUIRED

If there is an implied right angle, there is a maximum allowable deviation from it. ASME Y14.5M-1994 provides this. If the drafter does not like it, they should apply an explicit tolerance.

JHG

 

[powerhound]

ringman,

I don't think this note is legit. What does any of this say that general tolerancing doesn't say? You can't just specify the standard and then add a note such as this. It seems to be a misguided attempt to say everything that good GD&T can say without having to apply it to the drawing. It's not going to work.

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[ewh]

I agree that this is a superfluous note. You have to draw the line somewhere, and if it's covered by the standard, it is redundant to include it in the notes.

Chris, I agree that this may be confusing. The only way I can "interpret" (not "read" unfortunately) "PERFECT ORIENTATION AT MMC" is to consider it a case of a 0.000 positional tolerance at MMC, which is a legit callout, but one that I seldom see used. I was once called to the carpet for using it because the engineering manager couldn't grasp the concept that MMC was not intended to be met, only approached.

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[MechNorth]

Rule #1 only covers Features Of Size, not surfaces. So, if you have a surface shown 90-deg to another surface, what controls it? The statement "Perfect Orientation at MMC" would mean 0@MMC, but again only applies to Features Of Size.

If you are using GD&T on the drawing per Y14.5M-1994, there should be a general surface profile tolerance to cover all non-Features Of Size, and each Feature Of Size should be controlled directly. There is no need for a general angle tolerance when a general surface profile is invoked.

EWH, I get much the same reaction when I teach 0(M). I've found that showing a Normal Distribution curve to represent typical manufacturing results helps a lot.

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

http://www.profileservices.ca

 

[WHITMIREGT]

ASME Y14.5M-1994, PARAGRAPH 2.7.3c the note added to the drawing reads for the relationship between feature "PERFECT ORIENTATION (or COAXIALITY or LOCATION OD SYMMETRICAL FEATURES) AT MMC REQUIRED FOR RELATED FEATURES." Without this note there are no automatic geometric controls relatine one feature to another without GDT controls.

Paragraph 2.1.1.2 states that implied 90° surfaces are controlled by the angular tolerance in the title block.

Please note that the 2008 dimensioning standard is the same as the above.

 

[ringman]

Gary,

I am aware of the contents that you pointed out in the Standard and think I moderately understand and could apply them. However I have problems with the note that I mentioned in my OP and thus far have not found acceptance nor agreement on the interpretation of the note that I listed.

Do you feel the note to be acceptable as stated? Can you provide an interpretation of just what is intended by related surfaces when no feature control frames are used?

Thanks for your unput.

 

[MechNorth]

I believe, by nature of the other sections (a,b,d) that 2.7.3(c) is not intended as a general note, but rather as a note directly applied to the individual features to be grouped / related. In that way, relationships are clearly defined. Again, however, this only applies to Features Of Size, which means that you are controlling the relationship of the center planes or axes, not actual surfaces.

2.1.1.2, further on from the passage cited above, goes on to indicate "The tolerance on the feature associated with these implied 90-deg basic angles is provided by feature control frames that govern the location, orientation, profile, or runout of features of the part." In other words, it allows you to use either method as consistent with your standard methods. Unless you want wedge shaped tolerance zones (as in optics), using the general +/- angle tolerance to control the perpendicularity of surfaces is not the best answer. If you can live with a tolerance zone that grows as you move away from the intersection of the two surfaces, then by all means use +/- angle tolerances.

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

http://www.profileservices.ca

 

[WHITMIREGT]

Ringman,

This note should be pointed to a couple of features, otherwise it would apply to all features related to each other needs to be perfectly orientated etc. that is typically not a design requirement.

To reverse the subject,we could use a general note that state "PERFECT ORIENTATION (or COAXIALITY or LOCATION or SYMMETRICAL FEATURES) AT MMC IS NOT REQUIRED FOR RELATED FEATURES." because the drawing does illustrates perfect orientation etc. that is not really needed. I know the rule stated in Paragraph 2.7.3 "The limits of size do not control the orientation or location relationship between individual features" but not all individuals no all of the dimensioning rules. I know I'm preaching to the choir.

 

[ringman]

My concern is that this IS used as a general note. It nullifies the title block tolerance for implied angles, and does little more than confuse most who come into contact with it.

Without a stated relationship it is pure speculation as to the related features. IMHO

In line behind Kenat