Question regarding True Position Callouts

[brandnew1]

Hi,

i have a question regarding the attached pdf.

i'm uncertain about the true position call out for Datum D. Datum D is a plane and has to be .010 to Datum B (.50 Ref) and Datum C (diameter). Is this asking for the size of the plane to be measured and i get the center point and make sure it's 'centered' to Datum B and C? (based on researching planes to true position it appears that this should be a profile call out but someone indicated that true position of a plane is legal under ISO)

2nd question relates to the the diametrical true position call out. The way i'm viewing this is that the center of the diameter has to be within the .005 diametrical true position and there is a bonus if as the diameter moves away from MMC. What i'm not certain about is the call to Datum D again...

any help would be appreciated...thank you

 

[Belanger]

You're right. If D is a plane, then it illegal to apply a position tolerance to it. (If this were ISO that would be OK, but the datum feature symbol clearly indicates that it's ANSI style.)

Same for the second question: the datum reference to D adds no value to that position tolerance.

It looks like an older print ... is there any pushback you can have on the designers/engineers to straighten them out?

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

http://www.gdtseminars.com

 

[brandnew1]

Thanks Belanger...

This is actually a customers drawing and says copyright 1997 and i don't see anything related to what format to go with, thus i wasn't sure if this was based on ISO as well. (i'm not familiar with ISO since i just look at the Y14.5 standards).

i'm not an expert but if anything a novice at GD&T, so when i look at this and its from 1997 i'm wondering if the true position call out is for something else but accidentally attached to Datum D and since its from 1997 why no change all this time?

So i'm kind of stuck, i'll just let my GM know about the issue and see what happens from there...

 

[Belanger]

Yep ... that sounds like the best plan. One question: is the 1.25 dimension boxed on the actual print? If so, they were most likely trying to control the length of the threaded bolt/stud with the position tolerance (1.245 min and 1.255 max).

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

http://www.gdtseminars.com

 

[brandnew1]

Yeah that's what i was looking at first as well...i figure with TP call outs to feature control frames there would be BASIC dimensions, but it that dimension is not boxed and because it carries a two place dimension it ends up having a tolerance of +/-.030 (inches).
So i don't think a true position call out to .010 will tie into this dimension =)

 

[fsincox]

I am with JP.