Positon or Surface.
Positon or Surface.
(OP)
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
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





RE: Positon or Surface.
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.
RE: Positon or Surface.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Positon or Surface.
RE: Positon or Surface.
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.
RE: Positon or Surface.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Positon or Surface.
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.
RE: Positon or Surface.
Oh, I should have not posted anything today. It is better to stay quiet than make such communication noise. My apologies.
RE: Positon or Surface.
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
RE: Positon or Surface.
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.
RE: Positon or Surface.
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://f
RE: Positon or Surface.
Frank
RE: Positon or Surface.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Positon or Surface.
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
RE: Positon or Surface.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Positon or Surface.