Double Maximum Material Condition? 5

[Daekar]

During the inspection process I ran across several features (round slots and holes) which had not one, but two MMC symbols in the position block. That is to say, the second MMC symbol was not for a Datum of size, but in the same segment of the position block as the position tolerance itself:

|TP|DIAM .007(M)(M)|A|B(M)|C|

This appears in several places on the print, so I'm fairly certain it isn't a "typo." Does this mean the design engineer is intending to double the bonus derived from the size of the features?

Thanks for the help,
Adam

 

[dingy2]

Adam:

The feature control frame as described in not in compliance with either the ASME 14.5M- 94 or 2009 standard. I would suggest that you go back to the Designer and ask for an explanation. You will find out that the Designer just doesn't know.

If I were in your posiition (and I was at one time) disregard the second MMC.

Dave D.

http://www.qmsi.ca

 

[Daekar]

Dave,

Thanks for the quick answer! I think the print was drawn by a rookie engineer, and judging by the number of dimensions which were completely omitted in the original rev (added in ECOs later), he probably just needs more practice and constructive feedback. I'll let him know about the problem.... thanks again!

~ Adam

 

[axym]

That's a good one. Double the MMC bonus. Or possibly square it. Maybe it's some sort of "relativistic bonus tolerance" that is only significant if the part is accelerated to near light speed:

B = (MMC)^2

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[fcsuper]

It's possible that the second M was meant to be another symbol?

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[ewh]

"I think the print was drawn by a rookie engineer..." and also checked by the same engineer?

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[KENAT]

Don’t be silly ewh, we know that those in management long ago determined that checking is no longer required since people creating drawings these days are professionals and by checking their own work clearly see the wood despite the trees and don’t make mistakes, no matter how inexperienced or lacking in training. It must have been a computer error.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[ewh]

You're right, my mistake... must be Monday.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[Belanger]

There is a provision where the bonus tolerance can be capped at a maximum value, but this would be indicated by a number and the word MAX. So I suspect that it's just a mistake.

 

[weavedreamer]

And when the computer gets to the point where it blames it on another computer? . . .

 

[powerhound]

Belanger,

Please elaborate on your post. I haven't seen that one in the standard. Where is it?

Powerhound, GDTP T-0419
Production Manager
Inventor 2010
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[Belanger]

The idea of "capping" the tolerance is shown in the new standard in Fig. 6-15, or in the 1994 standard check out Fig. 6-42.

 

[powerhound]

Belanger,

Thanks, that's one I've never noticed.

As far as I'm concerned you get a star for that.

Powerhound, GDTP T-0419
Production Manager
Inventor 2010
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[PaulJackson]

Thanks for pointing that out Belanger! Ihad never noticed that either.

Paul

 

[dingy2]

I agree that Belanger deserves a star. Just something that I never noticed in the standard.

Dave D.

http://www.qmsi.ca

 

[axym]

This is quite obscure. I have a vague memory about seeing the "capping" thing before, but I've never thought it through until now.

Here's the example from the standard:

PRP|dia 0(M) dia 0.1 MAX |A|

So the intent seems to be that we want the surface of the feature to conform to a boundary, but we also don't want it to get too tilted. This really acts like two perpendicularity tolerances for the same feature, one at MMC and one at RFS:

PRP|dia 0(M)|A|
PRP|dia 0.1|A|

I guess the committee thought that having two different orientation tolerances on the same feature would be confusing. Inserting another tolerance value and the word MAX into the FCF, in just this one instance, is much more clear.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca