GD&T Parallelism Interpretation - Print which has a note: //|0.5 | A.

F

fyu111 - 2005

#1
I have been in discussion with our customer regarding the interpretation of the print which has a note: //|0.5 | A.

A is established as a plane per below.
| -- // 0.5 to A
O
| -- Datum A

It is my understanding that the top plane must fall within 0.5 of the plane Datum A with no respect to the actual physical location.
 
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Jim Wynne

Staff member
Admin
#2
fyu111 said:
I have been in discussion with our customer regarding the interpretation of the print which has a note: //|0.5 | A.

A is established as a plane per below.
| -- // 0.5 to A
O
| -- Datum A

It is my understanding that the top plane must fall within 0.5 of the plane Datum A with no respect to the actual physical location.
I'm not sure what you are asking, but you're correct about parallelism having nothing to do with location, or distance between the two planes. In general, if you're using a CMM, the datum plane is established and then points are taken on the other plane, and the result is simply the parallelism error. On a surface plate you would locate on Datum A and then run an indicator across the other surface.
 

Miner

Forum Moderator
Staff member
Admin
#3
JSW05 said:
I'm not sure what you are asking, but you're correct about parallelism having nothing to do with location, or distance between the two planes. In general, if you're using a CMM, the datum plane is established and then points are taken on the other plane, and the result is simply the parallelism error. On a surface plate you would locate on Datum A and then run an indicator across the other surface.
This is the correct description of parallelism. If this is still unclear, the following link can help explain graphically: GDT Link

When the distance between planes IS important, you would use the PROFILE callout.
 
#4
Hello fuy, and welcome to the Cove :bigwave:
fyu111 said:
It is my understanding that the top plane must fall within 0.5 of the plane Datum A with no respect to the actual physical location.
I agree. What about your customers interpretation? In what way does it differ from yours?

Slightly :topic: , I once had an argument with a designer about this. He refused to put a height figure on a drawing for the very reason that the surfaces in question were to be parallell. I asked him if his desk was parallell with the floor... :rolleyes: Hmmmm.... Was my tounge was sharper in those days? :eek:

Good graphics in that link, Miner

/Claes
 

Jim Wynne

Staff member
Admin
#5
Miner said:
When the distance between planes IS important, you would use the PROFILE callout.
In combination with basic dimensions, of course. Good ol' x-y coordinate dimensioning is usually best for defining distances between planes unless there's a particular reason for using profile, and there almost never is.
 
W

WWilliams

#6
//-.5-a

Your customer seems to think that some sort of basic dimension applies? Not with -//. You are right
 
F

fyu111 - 2005

#7
Yes, there is a basic dimension on the print which they are trying to hold to a tolerance. I have tried to explain that this would not apply using // but applies to a true position callout.

Thank you.
 
B

Bigfoot

#9
fyu111 said:
Yes, there is a basic dimension on the print which they are trying to hold to a tolerance. I have tried to explain that this would not apply using // but applies to a true position callout.

Thank you.
I'm still a little confused by what the question is. If it is about the parallellism callout the correct interpretation has been given. You reference "a basic dimension ... they are trying to hold to a tolerance", are they implying that the // is a basic dimension or is this another dimension that is a subordinate to the feature with the // tolerance applied to it? If you could copy the section (s) of the drawing & attach them for viewing it would be beneficial in our helping interpret what is being applied to what?
 
B

bmccabe - 2006

#10
In a past life I’ve been a designer, and later a technical drawing auditor.

I’m reading between the lines of your question.

The consensus of the group is correct. Parallel not an attribute of location. But, :caution: there may be conditions to your customer’s statements, look carefully at the drawing, and please read the following. :caution:

Rule number 1) Unless otherwise specified: GD&T always supersedes bock or basic dimensioning.

We all agree Parallelism has no relationship to location – So, :caution: both :caution: the orthographic dimension + tolerance of location, and the GD&T tolerance for Parallelism must be within spec (see foot note).

i.e. No point on the plane may exceed the location dimension, and all points on the plane must conform the Parallelism spec.

If your back is against the wall, See rule number 1 (the first three words) :ca: – They’ve saved my bacon more than once.

r/b

foot note – This fact often creates situations where the location constraint is much tighter than the parallelism requirement; negating the necessity to specify parallelism at all.
 
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