Profile of a Surface : Can I use "per unit area"?
Profile of a Surface : Can I use "per unit area"?
(OP)
Hi All,
First post, so go easy on me! ;)
I have a part with six nominally co-planar mounting bosses over a total area of approximately 450mm x 450mm.
I have received feedback from the supplier that they can hold the "flatness" of these bosses (their terminology, not mine) to ±0.05mm per 100 x 100mm area. Thus they propose an overall "flatness" tolerance of ±0.2mm for the faces of these bosses. This (just about) acceptable to us, so we would like to capture this on our piece part drawing.
I would prefer to use Profile of a Surface in place of a flatness tolerance for a couple of reasons; the ability to control position (using a basic dimension) within the same tolerance and also, most importantly, the implicit inclusion of co-planarity provided by Profile of a Surface (Sec. 8.4.1.1 of ASME Y14.5)
I am proposing setting a datum plane (Z) to be co-planar with all six boss faces and then applying one of the attached geometric tolerances to the surfaces. (please see attached image)
The issue that I am having is that ProEngineer only offers "per unit length" as an option for Profile of a Surface, not "per unit area" (which is offered when creating a flatness tolerance, for example).
Is "per unit area" not an acceptable modifier to a Profile of a Surface tolerance?
Logically I think it should be allowed, but can find no explicit reference to it in ASME Y14.5 (which does mention per unit length in 8.3.2.2.).
I have seen it used in other places (http://www.tec-ease.com/gdt-tips-view.php?q=112 for example), but wanted to come here and solicit some other expert opinions.
Thanks in advance for any help you are able to provide! :)
First post, so go easy on me! ;)
I have a part with six nominally co-planar mounting bosses over a total area of approximately 450mm x 450mm.
I have received feedback from the supplier that they can hold the "flatness" of these bosses (their terminology, not mine) to ±0.05mm per 100 x 100mm area. Thus they propose an overall "flatness" tolerance of ±0.2mm for the faces of these bosses. This (just about) acceptable to us, so we would like to capture this on our piece part drawing.
I would prefer to use Profile of a Surface in place of a flatness tolerance for a couple of reasons; the ability to control position (using a basic dimension) within the same tolerance and also, most importantly, the implicit inclusion of co-planarity provided by Profile of a Surface (Sec. 8.4.1.1 of ASME Y14.5)
I am proposing setting a datum plane (Z) to be co-planar with all six boss faces and then applying one of the attached geometric tolerances to the surfaces. (please see attached image)
The issue that I am having is that ProEngineer only offers "per unit length" as an option for Profile of a Surface, not "per unit area" (which is offered when creating a flatness tolerance, for example).
Is "per unit area" not an acceptable modifier to a Profile of a Surface tolerance?
Logically I think it should be allowed, but can find no explicit reference to it in ASME Y14.5 (which does mention per unit length in 8.3.2.2.).
I have seen it used in other places (http://www.tec-ease.com/gdt-tips-view.php?q=112 for example), but wanted to come here and solicit some other expert opinions.
Thanks in advance for any help you are able to provide! :)





RE: Profile of a Surface : Can I use "per unit area"?
One comment though to your profile FCF's:
Single common 'Z' for sure is not allowed per Y14.5. I would suggest splitting it into both segments similarly to fig. 7-50 in Y14.5-2009.
I hope you know the difference between having and not having 'Z' in bottom segment of profile FCF
RE: Profile of a Surface : Can I use "per unit area"?
If I understand you correctly, you want to make the six coplanar surfaces the common primary datum feature for datum Z. You want (or will accept) 0.4mm coplanarity overall between all 6 pads. You want 0.05mm flatness on each pad individually. Correct? If so, then you don't need per unit area; the first level of the composite control would be 0.4mm, and the second level would be 0.05mm, with INDIVIDUALLY added behind the fcf of the second level. The profile control needs a 6X (for '09) or 6 SURFACES (for '94) with the feature control frame, and preferably with 6 leaders or a phantom line showing the relationship between the surfaces.
If I have misunderstood the intent, pls restate for me.
Pmarc, pls explain why you feel a single common Z datum is not allowed. The use of multiple datum features resulting in a single datum is well understood in the standard.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Profile of a Surface : Can I use "per unit area"?
RE: Profile of a Surface : Can I use "per unit area"?
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Profile of a Surface : Can I use "per unit area"?
Taking an extract of Jim's post:
"If I understand you correctly, you want to make the six coplanar surfaces the common primary datum feature for datum Z. You want (or will accept) 0.4mm coplanarity overall between all 6 pads. You want 0.05mm flatness on each pad individually. Correct?"
Not totally correct.
My intention was to keep the 0.1 Profile of a Surface over the 100x100mm area that the supplier states they can hold this within.
The reason I want to retain this is that a couple of the bosses are within 100mm of each other so I want these two boss surfaces to be more tightly controlled with respect to each other than the 0.4 overall tolerance (to avoid any significant "step" over a relatively small distance).
I hope I have explained myself correctly.
Thanks again.
RE: Profile of a Surface : Can I use "per unit area"?
The problem is that unless your pads are actually large enough, you don't have a 100x100 surface area and therefore it wouldn't be understood (beyond your single supplier) what it means.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Profile of a Surface : Can I use "per unit area"?
Please look at attached picture - hope this explains what I meant.
http://fil
RE: Profile of a Surface : Can I use "per unit area"?
It also has the advantage of avoiding me having to try and achieve something that ProEngineer's geometric tolerancing configuration is preventing me from doing! (Apply a per unit area tolerance to a Profile of a Surface).
RE: Profile of a Surface : Can I use "per unit area"?
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Profile of a Surface : Can I use "per unit area"?
I never knew where that symbology came from (not the std) I have allways assumed it was just a CAD package issue and therefore would have to be allowed. I realize most packages now are updated but I run into this all the time when the standard changes, like right now SW does not allow the "all around" symbol on dimension leaders only note leaders and it doesn't even support "all over". I have to ask, where does it say it can't be done that way?
Frank
RE: Profile of a Surface : Can I use "per unit area"?
Paragraph 3.4.4 of Y14.5-2009 says: "A composite feature control frame contains single entry of a geometric characteristic symbol (position or profile) followed by each tolerance and datum requirement, one above the other".
Don't know if this is sufficient for you but for me is.
Additionally some figures in the standard somehow supports my point of view (7-42, 7-43, 7-44, 7-50).
The only thing I do not like in 3.4.4 is that it seems to exclude composite flatness or straightness FCF's as shown in fig. 5-4 and para. 5.4.2.2 for instance. Unless these FCF's should not be called composite...
RE: Profile of a Surface : Can I use "per unit area"?
Frank
RE: Profile of a Surface : Can I use "per unit area"?
Frank
RE: Profile of a Surface : Can I use "per unit area"?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Profile of a Surface : Can I use "per unit area"?
If flatness and/or straightness FCF's with per-unit length or area refinements would not be called composite, then can profile of a surface with per-unit area refinement in the lower segment be called composite? If it should not be called composite too, then maybe 3.4.4 does not apply here? Hmm...
But seriously, coming back to the main topic, I do not think that even if there was a single common datum reference for both segments of profile FCF in OP's question it would create any confusion. I believe the intent would still be clear.
It is only a matter of how legal one wants to be in using this particular concept of GD&T.
RE: Profile of a Surface : Can I use "per unit area"?
I think the difference is because a composite FCF for profile or position implies that the datums in the lower segment have an "orientation-only" role to play. Since flatness and straightness never reference datums, they aren't composite in that sense.
Which brings up your good question: If we are showing a single profile symbol in front, but merely want to use the lower segment for a per-unit refinement, should it really be called composite? Probably not, methinks. But this terminology question is a very small aspect of the discussion.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Profile of a Surface : Can I use "per unit area"?
Frank
RE: Profile of a Surface : Can I use "per unit area"?
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Profile of a Surface : Can I use "per unit area"?
I do not have 1982 version so cannot say.
Also cannot find it in any of existing ISO GD&T standards.
RE: Profile of a Surface : Can I use "per unit area"?
A single datum reference for multiple lines was legal per first edition of ISO 1101 issued back in 1983. Figure 43 in clause 9.2 shows this. The most recent edition of this document (2004) does not show this practice any more.
RE: Profile of a Surface : Can I use "per unit area"?
Frank