Positon or Surface.

[indkitty]

Hello, I have recently started to study GD&T. I have query , which one should we use positon or surface in this particular sketch.

My senior colleague says, we should use postion. I believe we should surface and we can refine if need be.

Ignore 0.20 tolerance which is with position.

clarification with why we should use positon or surface is much appreciated.

krishna
Beginer

 

[drawoh]

indkitty,

There is no such thing as a surface tolerance. The term is profile. That is what I would use. The positional tolerance locates features of size.

JHG

 

[MechNorth]

Assuming you are using ASME GD&T, you must use profile. Position can only be used on a feature of size (directly opposed points and a size limit; these surfaces are not directly opposed). In ASME, position locates a center plane, axis or center point, NOT a surface. In ISO, position can be used to control a surface location, but not in the way indicated as I recall.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[indkitty]

My apologies with the term surface, I meant profile.

 

[pmarc]

Saying shortly, I am with Jim (MechNorth) on that. Regardless whether you work to ISO or ASME, position, as it is applied on your left sketch, does not even control surface which is the case on the right sketch.

Your left sketch is more or less OK, if ASME governs the print. To make the right one in conformance with ISO GD&T, copy the right one and simply replace profile of surface symbol within feature control frame with position symbol.

 

[MechNorth]

Pmarc, the one on the left is a stepped surface, not a fos. Position can't apply there either. Tks for clarifying the ISO position on the right; I was thinking that it was a direct replacement, but I haven't used ISO in a very long time.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[pmarc]

In order not to mislead anybody, there should have been: "To make the left one in conformance with ISO GD&T, copy the right one and simply replace profile of surface symbol within feature control frame with position symbol.

Jim,
Yes, I agree. In this particular case position FCF cannot be attached to size dimension since controlled feature is not a classic FOS. Though one could argue that there is nominally at least on pair of lines opposite to each other. But I do want to start the discusssion about what is and what is not a feature of size again.

 

[pmarc]

Another edit: "Your right sketch is more or less OK, if ASME governs the print. To make the left one in conformance with ISO GD&T, copy the right one and simply replace profile of surface symbol within feature control frame with position symbol."

Oh, I should have not posted anything today. It is better to stay quiet than make such communication noise. My apologies.

 

[fsincox]

pmarc,
I was thinking the same thing as you per our last discussion on this issue. I have been following here to see if it still was true, position can be used under ISO to locate the surface but is would be shown as the the profile was above, with the leader to the suface and basic dimensioned, as far as we know?
Frank

 

[CheckerHater]

Frank,
You are right,
Position FCF aligned with dimension like on the left sketch refers to derived feature like centerline.
Since on the left sketch basic dimension applied to step, the whole call-out is illegal IMHO (where is the center of a step?).
So you may apply position to the surface, but FCF has to be arranged like profile on the right sketch in order to refer to entire surface.

 

[pmarc]

Frank,
Look to attached pdf. There are 2 very similar figures in ISO 1101:2004 and Y14.5-2009 which nicely show the difference of Profile and Position application for planar features according to both standards.

As far as I recall there was a statement somewhere that according to ISO profile theoretically could be used too - it would not be a cardinal sin - however it is rather reserved for features of more complex (curved) shapes.

http://files.engineering.com/getfil...c28-46e806f3222a&file=Profile_vs_Position.pdf

 

[fsincox]

Thanks, guys. I find it hard to believe the ISO would not allow profile as an option, thank you for the example, pmarc.
Frank

 

[MechNorth]

If I recall correctly, at one time ISO prohibited the use of profile on anything but an "irregular" surface. They have softened their position a bit, but still don't encourage its use as we do in ASME. One of the ways in which ISO decided to detour from what was already established in ASME; when they started developing the actual ISO standards, they started with the ASME doc and made their own way from there.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[fsincox]

Jim,
Interesting, most of the companies I work with are not too keen on profile either. Just the other day I tried to convince our outside vendor to accept profile on a conical gear as would seem to be the preference here, he said:
"So, You want to put a profileometry (sic) callout on it? we can't measure that."
Profile does not seem to be widely accepted around here, I am pushing it with our people internally now, it is easier when I explain it is just "basically, true position of a surface", they seem to get that better.
Frank

 

[MechNorth]

Yup, Frank. There's still resistance in many pockets when I teach, at least initially. By the time I'm done they are so well versed in Profile that they start to push for its further use. In some instances where other trainers have preceded me, I quickly realize that the previous trainer was not GDTP of any level, and have to undo the damage done long ago. Fortunately I've been uniformly successful.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[indkitty]

Thank you all, for your response, attachments.