Datum reference frame for position on thin parts...
Datum reference frame for position on thin parts...
(OP)
Lets say we have a simple part that is a thin round disk with one or more hole patterns. Lets call the bottom surface Datum A and the major O.D. Datum B.
Using position to locate the holes, is it necessary to use Datum A in the FCF?
Using position to locate the holes, is it necessary to use Datum A in the FCF?
lightweight, cheap, strong... pick 2





RE: Datum reference frame for position on thin parts...
John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Datum reference frame for position on thin parts...
RE: Datum reference frame for position on thin parts...
lightweight, cheap, strong... pick 2
RE: Datum reference frame for position on thin parts...
If you omitted datum A, then B would be primary. Think of how that might change the way a fixture or gage grips onto the part.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Datum reference frame for position on thin parts...
If you like more practical point of view, your “thin flat part” is most likely some sort of lid or gasket.
Functionally it is leaning against flat mating surface and your datum framework simulates that condition: lay flat first, make sure bolts are fitting thru holes second.
All of the aspects of this were already discussed here so many times, I am out of convincing examples.
RE: Datum reference frame for position on thin parts...
lightweight, cheap, strong... pick 2
RE: Datum reference frame for position on thin parts...
For datum precedence concept, you may want to take a look to this thread for example:
http://www.eng-tips.com/viewthread.cfm?qid=354287
Just keep in mind that the discussion was about ISO, so don't let the concentricity symbol (shown in my picture posted 29 Oct 13 17:45) scare you.
RE: Datum reference frame for position on thin parts...
And how does the part assemble with the mating parts? Does it not sit flat on Datum A (full area contact)?