Question regarding starting point to measure based off BASIC dimensions
Question regarding starting point to measure based off BASIC dimensions
(OP)
Hi All,
Is it right or safe to just begin at an arbitrary point (based on basic point) that is marked at a specific distance and measure all other values based on this beginning point?
Attached i have a blueprint for the part and i just want to make sure that i start measuring the part accurately. However these angles and radius' are BASIC which i understand to be 'theoretically' exact, however in manufacturing this isn't realistic and usually i see a FCF tied to these basic dimensions which allows for some tolerance.
So for example can i measure the outer diameter and create a point that is 8.8 from this diameter and then measure other radius' and angle based on this point?
thanks for the guidance
Is it right or safe to just begin at an arbitrary point (based on basic point) that is marked at a specific distance and measure all other values based on this beginning point?
Attached i have a blueprint for the part and i just want to make sure that i start measuring the part accurately. However these angles and radius' are BASIC which i understand to be 'theoretically' exact, however in manufacturing this isn't realistic and usually i see a FCF tied to these basic dimensions which allows for some tolerance.
So for example can i measure the outer diameter and create a point that is 8.8 from this diameter and then measure other radius' and angle based on this point?
thanks for the guidance





RE: Question regarding starting point to measure based off BASIC dimensions
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Question regarding starting point to measure based off BASIC dimensions
Just in addition, sorry for the not so smart question, but when a profile of surface is an Unilateral Tolerance (Outside) does this make the BASIC dimensions +.010 / -.000 (for the O.D.) & +.000/-.010 for more of the ID (8.5 & 8.6 radius')? i see this for just straight dimensions like the radius' however how does this work with angles? How does a tolerance get to the angles or radius to the holes found in the part (i'm just trying to wrap my thought about how the profile of surface is an unilateral tolerance which would make the part larger only in one direction but how the perspective that this is viewed seems to change.
RE: Question regarding starting point to measure based off BASIC dimensions
thank you again
RE: Question regarding starting point to measure based off BASIC dimensions
When it comes to angles, you can really translate the profile's linear tolerance of .010 to an angular tolerance. So while a basic angle helps establish the perfect outline, it's usually better to just think of the tolerance as a bandwidth of .010 splashed all the way around. Keep your thinking in this linear mode and that avoids some of the pitfalls.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Question regarding starting point to measure based off BASIC dimensions
thank you for your answer.
i just wanted to verify that you mean't "can't" instead of 'can' in the following sentence:
"When it comes to angles, you can really translate the profile's linear tolerance of .010 to an angular tolerance". i just want to make sure because the sentence says 'can' but the way it is explained sounds like can't but i could be wrong here.
thanks again
RE: Question regarding starting point to measure based off BASIC dimensions
And this is because a profile tolerance is in inches (or millimeters), not degrees.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Question regarding starting point to measure based off BASIC dimensions
i found an article on the web written by you (Belanger) that indicated, "This means that there is a profile zone imposed around the entire perimeter of the part, but only in the left-hand view. [in the example there are two images and the all-around is pointed to the left image]" (http://gdtseminars.com/blog/)
So with the part drawing i'm dealing with, the profile zone is only dealing with the right-hand view (from previous pdf uploaded in original post) - however the example from the link did not tie the profile to datums.
Here is where i think i may be over analyzing this (based on a simple drawing i attached - this part is a small segment of a larger diameter with this unilateral profile tolerance)
Datum A is the plane with a flatness of .005 and datum B is diameter of .498 +/- .001. Diameter B is theoretically 8.8 from the center point of this large diameter which is only given on the drawing by the radius' which are basic as well.
So the main question i have, does this 8.8 BASIC dimension off of datum B have a tolerance? And also does the unilateral profile tolerance affect all portions of the part (including datum A and B?)
RE: Question regarding starting point to measure based off BASIC dimensions
I'm not sure if your part is a version of a torus, but let me know if I'm getting at the gist of your question.
The other question you had near the end was about the 8.8 basic dim. Based the snippets I've seen, I think the 8.8 goes FROM datum B to the imaginary vertex off to the right. From there the other basic radii travel back to the left to establish the perfect profile that the GD&T will then apply to. So there is no tolerance on the basic of 8.8. It's just a stepping stone to describe the rest of the part, and that's where the real tolerance resides.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Question regarding starting point to measure based off BASIC dimensions