Attach surface profile FCF to feature of size dimension?

[JBATX]

At my company we use a lot of surface profile. I will frequently see drawings where the surface profile FCF is attached to the dimension of a feature of size(a width or a diameter). The intent is to control the surfaces of that feature. If it is a width, both surfaces would have the profile applied bilaterally. If it is a diameter the profile would be applied to the circular profile. Is this a valid callout? There are no examples of this in ASME Y14.5M and I haven't seen this application anywhere else.

 

[Belanger]

That would not be a valid way to call it out. What you describe is very common for position, where the feature control frame is placed directly beneath the size callout. But profile should be tagged to the surface.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[drawoh]

jdborchert,

I apply profile tolerances to features of size, especially diameters. This is interpretable. The actual profile must be contained within the width of the profile specification. Everything is located from the specified datum features. Size and position are controlled. Typically, my requirement is for a cut-out, the accuracy is not critical, and my profile tolerance is sloppy.

A profile tolerance applied to a feature of size, probably is not equivalent to a feature of size with a specified size tolerance and a positional tolerance.

Scenario A:
[Ø100] [profile|0.8|A|B|C]

Scenario B:
Ø100.2/100.1 [pos|Ø0.8|A|B|C]

Scenario C:
Ø101.6/100 [pos|0(M)|A|B|C]

The above three examples are not right or wrong. They meet three different requirements.



--
JHG

 

[pylfrm]

jdborchert,

I would say it's invalid, mainly due to the following:

Where an equally disposed bilateral tolerance is intended, it is necessary to show the feature control frame with a leader directed to the surface or an extension line of the surface, but not to the basic dimension.

However, ASME Y14.5-2009 does show another method in Fig 4-4. There, the side of the FCF is attached directly (without a leader) to an extension line from the feature. I've always considered this valid as well, despite what the above quoted paragraph says.

Regardless of validity, I think the method you describe isn't very clear, especially in the case of a width.

Out of curiosity, are the dimensions in question basic or toleranced?

drawoh,

I agree that it's perfectly valid to apply profile of a surface to a feature of size, but the question is about placement of the FCF. For your Scenario A, how would you actually show it on a drawing? What if it were a width instead of a diameter?


pylfrm

 

[drawoh]

pylfrm,

I apply the profile tolerance to my diameter specification. The diameter, obviously, is a basic dimension. Attaching the FCF to the circle works too.

In the case of something with a width, presumably, there is a height too. On a cut-out, I want the profile to apply all the way around. I attach the FCF to one edge and I show the all-round circle.

If I am controlling the width separately from the height, it all depends on why I am doing so. I suppose I would attach the FCF to each side.

--
JHG

 

[jassco]

Hi, jdborchert:

Surface profiles shall not be attached to dimensions. As Belanger indicated, profile should be tagged to the surface. You may attach position FCFs to dimensions as long as they are BASIC dimensions. Although it does not hurt to attach profile FCF to surfaces of a feature of size, it is an overkill. You should consider using a position FCF instead. If you do decide to attach surface profile FCF to surfaces of a feature of size, the size must be BASIC, otherwise, one has redundant definitions.

Best regards,

Alex

 

[JBATX]

drawoh - It's not the application of profile to a feature of size that is the concern, but the placement of the FCF. I am seeing the FCF attached to the basic dimension like a position tolerance FCF. When you say that "I apply the profile tolerance to my diameter specification", do you mean that you attach the FCF directly to the basic dimension like you would a position FCF?

It seems that the consensus is that this is not valid which confirms my initial thoughts. I never liked this notation and don't do it on my drawings but see it all the time. It looks like paragraph 8.3.1.1 pretty explicitly prohibits the notation. Hopefully that will be helpful in convincing others that the notation is invalid.

 

[drawoh]

jdborchert,

I sometimes attach the profile FCF to diameter dimension. As noted above, the diameter is basic. The specification is not ambiguous. The FCF controls the diameter, only, but it controls the entire diameter.

--
JHG

 

[Belanger]

Fig. 8-24 of the standard does show profile and position tagged together, so in that sense I see what drawoh is saying. But in the philosophy of GD&T, profile always applies to the surface itself.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[JBATX]

Just to clarify, here are a couple of examples of what I am seeing.

 

[drawoh]

jdborchert,

Did you delete the datum references, or were they not used?

My concern about that first one in particular is that it is very accurate. An accurate feature of size does not necessarily need to be positioned accurately. Your MMC/MMB condition is Ø.593 clearance exactly at nominal position. Your LMC/LMB condition is Ø.597, again exactly at nominal position. Is that what you need?

The second figure is a weird way to show a hole for a countersunk screw. I take it you have a profile on the countersink itself? The head diameters of flat head screws are not accurate. The countersinks are cut with a countersink tool. The angle you get is whatever the tool cuts. Are you really going to inspect it?

When I call up a countersink for flat head screws, I am either trying to make the screw sit approximately flush so that it looks good, or I am trying to assure a mount face, with the screw always sitting below flush. I use a [±][ ]tolerance, and I fudge the diameter. If my screw sits neatly in the hole, I am happy.

--
JHG

 

[JBATX]

drawoh,

I didn't delete the datum references - there are none (that's a whole different topic of conversation). These examples are not from my drawing. I just pulled them from one of the drawings I have seen recently to illustrate how I am seeing surface profile callouts attached to dimensions. From my understanding this is not a valid notation and most on this thread seem to agree. Do you use surface profile this way?

 

[drawoh]

jdborchert,

I cannot visualize a profile tolerance without datums. A profile applies with respect to something. That second specification showing profiles of .008 and .002, is especially meaningless. The whole point of composite FCFs is that the two specifications use different datums.

If you add datums, the tolerances you show would mean something. I do not know why I would call that up on the drawing.

thread1103-314750

--
JHG

 

[JBATX]

Like I said before, using surface profile without datums is a whole different topic of conversation - with lots of opinions on both sides of that debate.

My particular question had to do with attaching the surface profile FCF to the basic dimension as shown in the examples above. Regardless of the datum references (imagine they are there if it's helpful), is it appropriate to attach the FCF to the basic dimension?

 

[Belanger]

A profile tolerance can certainly have no datum references. In that case it would control form. (And if it applies to a sizable item, such as the images given, it controls size as well as form.)
What I don't get is the composite profile callout: the .008 and the .002 are in conflict. That's where a datum might be helpful, such as referencing one or two datums after the .008.
Since it's 2X, maybe they are trying to align the two holes to each other, and then size them individually, but that's not the right way to do it.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[JBATX]

I understand how surface profile can be used without a datum to control form and size. At my company many engineers use surface profile extensively to control form, size, and location. The idea is based on invoking the rule of simultaneity - since all of the surface profile callouts have the same datum structure (i.e. - no datum references) they are to be interpreted as simultaneous requirements, therefore controlling the size, form, and relative location of every feature. The composite profile callout is interpreted to control the location in the upper segment with a refinement to the size/form in the lower segment. I understand the premise but there are varying opinions on whether it is "legal" and how to interpret the use of surface profile in this way. I think it is poorly understood, frequently overused, and often imposes very strict requirements that are unnecessary but it is definitely accepted and promoted in some circles. But again, that's a different topic of conversation than what I am specifically asking about here.

I'd like to get further clarification on my original question - is it appropriate to attach the surface profile FCF to the basic dimension? Most of those that responded said no but, drawoh said: "I sometimes attach the profile FCF to diameter dimension." Does anybody else do this or have an opinion and/or reference as to whether this is an acceptable notation?

Here is another example with a datum reference. In this example datum A is the axis of the larger diameter. Regardless of the datum structure or the tolerance, the question is: Is it appropriate to attach the surface profile FCF to the basic dimension?

 

[drawoh]

jdborchert,

I have no objection to the format. If datum[ ]A is a diameter further down the shaft, the profile controls the size and the position of the Ø.313[ ]feature. The specification can be interpreted and inspected.

Would I do that? Usually, I specify the feature size, and the position, separately. Usually, they are not of the same importance to me, and one will be tighter than the other. If positioning of this thing is critical, maybe it is less critical when the FOS is at LMC/LMB, something you would account for in a separate positional tolerance.

Maybe the specification shows what they really need.

--
JHG

 

[Belanger]

As mentioned before, the standard never shows it that way, but I would understand what you are controlling. So I guess that's two votes in the affirmative.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[pylfrm]

jdborchert,

I also think your latest example with the .313 diameter is fairly unambiguous, so I'd like to revise my answer slightly:

Regardless of validity, I think the method you describe isn't very clear, especially in the case of a width.

Changes to:

Regardless of validity, I think the method you describe isn't very clear when the dimension involves more than one surface.​

In your example with the .595 width, I don't think it's completely clear that the profile tolerance applies to both surfaces. I think it would be even less clear if the dimension line arrowheads had been on the outside of the extension lines instead of on the inside.


pylfrm