default profile callout

[DesignBiz]

For drawings that might have a default profile callout, how is the specification in section 6.5.1 para. (a) reconciled?

(a) "An appropriate view or section is drawn showing the desired basic profile."

I take it that this is in reference to the 1st sentence of the 1st para. in 6.5.1;

"The profile tolerance specifies a uniform boundary along the true profile within which the elements of the surface must lie."

DesignBiz

 

[KENAT]

Are you talking about true drawings or hybrid drawing/MBD?

For a true drawing then you need a view that shows the desired basic profile. Just instead of having an FCF attatched to that geometry in that view, you rely on the general note.

Or am I missing a trick question here?

For MBD you'd have to also apply 14.41.

(Please note, I'm not completely sold on the idea of routinely having a default profile on drawings, but I don't see your above question as the deciding factor on why you can't)

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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

What is Engineering anyway: faq1088-1484

 

[DesignBiz]

KENAT,

This is not a trick question, however I would like to consider comments from others. From what you write,
I think we are in the same camp.

Our drawings callout tolerance of position for holes. All other features are claimed to be the master and basic based on the math data (CAD model). A general profile callout is used to default to everything else. Sometimes inexperienced folks dont even bother to identify Datums A, B, and C which are referenced in the default profile note.
I have found out that if the drawing doesnt define the datums, then it is suppposed to be defined in the model with 3D GDT (Ungrahics here). It isnt. I question on how the callouts are suppposed to be interpreted. This falls on deaf ears.

I say as you have that at a minimum the view on the drawing representing true views of profiles left to default should be present.

I believe this a decision to save time by not having to actually spend time dimensioning. However in the effort to save time I see many times that even part functionality is not thought about. In the long run just more "hybrid" drawings that have little to no meaning.

Just wondering what folks do with these drawings when they are used to create parts. Astonishingly as I have asked "who" inspects and "how" is it inspected, more often than not nobody seems to know who or how? Sad for a Fortune 100 company.

DesignBiz

 

[KENAT]

So you are talking about at least partial MBD? Definitely look at Y14.41-2003 if you haven't already, I can't seem to find much now but 6.2.6 does mention that general notes may include tolerances for the entire model and 10.1 mentions general geometric tolerance.

I thought it said more somewhere about default surface profile notes but I can't find it now. You've got me doubting myself.

In Y14.5M-1994 look at 6.5.4, it appears that datum references aren't always required. However, in this case, I share your concerns about repeatable inspection etc.

I have found out that if the drawing doesnt define the datums, then it is suppposed to be defined in the model

Could you cite a reference for this, as I believe it may conflict with 6.5.4 in 14.5 above, unless 6.5.4 is only allowing for use of surface profile without datums in coplaner controls (like flatness for multiple surfaces). I did work on a hybrid model/drawing MBD with a surface profile but no datums a few months back, it was an interim drawing until we could get some datum features cast in for use to reference.

However, my comment about having a view showing the profile was talking about stand alone/fully dimensioned drawing not MBD.

I had a thread recently thread1103-239768 which may have some relevant info, but I think you already posted there.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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

What is Engineering anyway: faq1088-1484

 

[DesignBiz]

KENAT,

There is not a Y14.5m standard that I am aware of regarding the datums attached to 3d models. This is internal to this company and refers to the capability to attach GDT datums to features of the actual 3D model. These datums can be viewed if the correct software switches are turned on independently of the drawing.

As to my initial question regarding partial dwgs that reference the Y14.5 standard,as I have described, and what do the profile defaults apply to. Considering that this line of thinking eliminates drawing views that desfine a particular profile, is this legal and understandable according to your knowledge of the standard?

Section 6.5.4 does mention use of datum reference for profile callouts that control orientation and/or location.
This is the case for us. No features, except for holes are defined on a drawing. Additionally we do not reference Y14.41 and unfortunately I dont have access to a copy at this time.

DesignBiz

 

[KENAT]

Doing partial MBD without invoking Y14.41 and relying on the 94 version of 14.5 sounds problematic. Fundamentally Y14.5-94 isn't set up to support that and I suspect you'll find quite a few issues like this if you look close enough.

However, you mention an internal company standard, if well written it's entirely possible this company standard covers these types of issues.

Without knowing what your internal company standard says it's difficult to give much input.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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

What is Engineering anyway: faq1088-1484

 

[JLang17]

I'm going to jump in here and ask a question. On the drawings I've been working on I would like to apply a note that controls flatness of all surfaces. Is there any preference to flatness vs profile when doing this? I assume a profile callout without referencing datums accomplishes the same thing as a flatness callout.

 

[DesignBiz]

KENAT,

Unfortunately this isnt even a company standard. Nothing is written anywhere. It is a verbal edict.



DesignBiz

 

[KENAT]

DBiz, then you have my sympathy. I actually want to update our in-house DRM to try and give guidance on hybrid MBD as at the moment, most people do a crummy job of it. I do intend referenceing 14.41 for what it's worth - it doesn't answer all the questions and seems aimed more at CAD developers than actual users as I think fcsuper has put before.

Jlang, might be better for a new thread but simplistically. For a single surface, flat to itself, arguably either would probably work but flatness would probably be better understood by the masses and this is it's intended application. If you have coplaner surfaces you want flat 'to each other' then you need to use surface profile see 6.5.6 of ASME Y14.5M-1994.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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

What is Engineering anyway: faq1088-1484

 

[DesignBiz]

JLang,

I personally dont like general defaults as a shortcut. If you are going to take the time to label a surface and then reference that surface to a note; then why not just add the GDT flat control while your at it and eliminate possible confusion? If its important enough to identify a surface for a tolerance that is typically associated with flatness, and the associated costs of that tolerance, why not take the time to identify it?

If it is flatness that you want to control, then why not keep it simple and specify flatness.

Obviously there is more ways to control a feature than just one and it would be up to the individual when it comes to a preferred way, not withstanding that functionality be considered foremost.

DesignBiz

 

[DesignBiz]

Thanks for your inputs KENAT !

DesignBiz

 

[JLang17]

My intention isn't to add a note to the surface and reference that to a flatness control. My intention is to place a flatness control under "Unless otherwise specified..." or something similar.

But ya, I was just curious if there was a preferred way in the GD&T world. Flatneses it is.

 

[KENAT]

Be carefull applying a default flatness unless you really need it, it may add cost. Also remember that by definition you get flatness within size tolerance anyway.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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

What is Engineering anyway: faq1088-1484

 

[fcsuper]

DesignBiz,

You don't by any chance happen to work at a company who's name is a delicious fruit, do you?

In any case, a general Profile FCF has to be associated with said datums. From what I've seen of drawings that rely on a general Profile callout, orientation of the part to the datums is almost always NOT considered, which makes the callout pretty useless, even when datums are placed on the print. Even when invoking 14.41, this is an issue.

Each orthogonal view should have its own profile fcf. These can be generically stated in the notes, but you'll need at least 3 Profile FCFs to account for each view fundamental orientation of the part (Front, Right, Top). You don't need any more than this because those three covers both direction for each orientation.

Without somethimg more sophisticated like this, you'll have a nearly unenforcable general spec.





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

 

[DesignBiz]

fcsuper,

I agree with your comment and would gladly have 3 basic views for orientation which these drawings commonly do not have. I have been troubled that most creators of drawings, and most unfortunately checker's at this point, don't understand the need these days. My position is to have the minimum views for part definition. In some cases where the true surface profile shows up in a view other than the basic views, it is necessary to create an appropriately projected view showing the profile.

Notice has been given for the lay-off of about 100 of the senior people here. For this particular group, a college grad, less than 3 months out of school, has been assigned as the checker. I am all for education, however experience doesn’t seem to count for much these days. IMO corporate greed continues to over-ride common sense.

Apologies for the rant (although it felt good) and thanks for everyone's comments.



DesignBiz

 

[axym]

DesignBiz,

Wow, you sure like opening up cans of worms!

To address your original post, I don't think that all of the statements in 6.5 and 6.5.1 can be reconciled when a default profile callout is used. Default profile callouts apply profile (I assume we're talking about surface profile) in a way that is fundamentally different from what was envisioned when the text of Section 6 was written.

If you read sections 6.5, 6.5.1 and 6.5.2 (which it looks like you have), the disconnect between the definition of profile and the way it is commonly applied becomes apparent. A basic profile is defined as a 2-dimensional outline in a given view or section view. Surface profile was intended to apply to surfaces with constant cross section - line profile was suggested for surfaces with varying cross section. However, most of the applications of surface profile that I've seen - and where it is really useful - are on complex surfaces. In these applications, the true profile is a three-dimensional feature and the surface profile zone is a three-dimensional shell around it. This is quite practical with 3D CAD models and 3D metrology systems, but one could argue that it goes against the definitions in Section 6.

The default profile tolerance approach takes this idea of the 3D shell and applies it to the entire part. The true profile is the CAD model - an integrated set of surfaces. The profile zone is a three-dimensional shell around the entire CAD model - an integrated set of zones if you will.

Regarding datum references, most default profile tolerances I've seen had datum references but some didn't. If there are no datum references, then the zone is still a 3D shell but it doesn't have to be aligned to any particular feature. It's kind of like the all-around profile tolerance in Fig 6-12, but without the datum reference.

Verifying these general profile tolerances can be a pain, but it is possible. It used to be done on flat, thin parts using a template method, where a 1:1 plot is made of the nominal part geometry and the offset profile zone, and the part is laid on the template. If you can get all of the edges to fit within the zone simultaneously then the part passes the profile tolerance. In 3D, this can be done using coordinate metrology, where points are scanned on the part and then the software fits the point cloud to the model.

Like it or not, you're going to see default profile tolerances more and more.


Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[KENAT]

"For this particular group, a college grad, less than 3 months out of school, has been assigned as the checker."

Wow, I'm glad I took of my old signature line of "probably the least qualified checker you'll ever meet", I think this guy gets to use that now.

Your management clearly doesn't have a clue, much like mine, which is why I have a feeling that if our sales don't pick up I'll be out the door soon.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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

What is Engineering anyway: faq1088-1484

 

[DesignBiz]

Axym,

You're right; I like to hear the comments of more or less controversial topics that pertain to Y14.5m standard. "opening cans of worms makes wince, while "stirring the pot" makes me smile, as your comment did.

I particularly find your point of view from quality engineering's perspective interesting. Mainly because I have had the least input from the quality people in my environment. Thank you for your well written comments!

KENAT,
I hope you're not "out the door" soon, unless it’s your choice. I find it increasingly difficult to work in an environment moving towards stupidity.

Ignorance is okay, it's curable, unfortunately stupidity is forever.


DesignBiz

 

[ewh]

And I thought KENAT was having a hard time of it...
Can this recent grad even create a legitimate drawing?

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

 

[DesignBiz]

Funny you should ask. Short answer...no.

First design of flexible tube looked like a bow; like when you tie a shoe string. The first drawing, not so good.... lots of stuff crossing each other. I confusing looking drawing at best.

Nice young man with potential... just no experience yet.


Makes you wonder about how leadership can justify these decisions.

DesignBiz