Gilson is referenced in the link that 3DDave provided.
Going back to the 2 dim stack. Assume both dims are produced with a process capability Cpk of 1.33. At this Cpk 99.4% of the dims will come within their tolerance. This would mean that the confidence in the 2 stack would be higher that 5...
John-Paul,
You are correct. RSS Theory does not tell us the percentage of the measured values one needs. Knowing the Cpk would allow one to figure out the percentage of measurements. In the example I proposed, with a little quick research after you posting, the 2 dims would require a Cpk of 1 so...
Lets say we have a 2 dimension stack to evaluate. Each tolerance in the stack is the RSS for the dim. That would mean 99.7% of the measured values for the dim would fall with the RSS tolerance. So now we complete a RSS calculation with the 2 dims. The confidence for the result would be...
Thanks for the valuable feedback and comments!
Belanger makes a really good point about caveats. People will often do a RSS calculation without meeting or understanding the assumptions
(I prefer the term "rules") for the analysis. I have observed people changing tolerances from equal bilateral...
Thanks dgallup,
From researching I was inclined to accept that 2 bilaterally toleranced dims would be acceptable. Stats usually generate more reliable results with increased number of reasonable data but one does not always have a lot data to use.
We are working out the standard deviation of nominal dims with equal bilateral tolerances. The RSS sums the variances of the pooled dimensions and the square root of the is the standard dev. of the pooled(assembly. You most likely know that already. My stats books do not state anything about...
When calculating a RSS is there a minimum number of tolerances than can be used? I have seen RSS results with 2 tolerances(the very minimum) used for the calculation and have been told that an RSS should not be used unless there are 5 or more tolerances used in the calculation. Nobody where I...
I agree with Tmoose.
Please explain how a bilateral tolerance is vague and subject to interpretation. I often hear very lengthy discussions in the product design group on how to apply and interpret GD&T. This does not seem to happen when using +/- tolerances.
L. Jones
Hello All,
I am trying to enforce a small displacement on a thin cantilever beam in the horizontal direction, then apply another displacement in the vertical direction.
I was trying using subcases but the subcase manager only allows loads to be managed and not displacements. How can I apply...
3DDAVE,
When you say VSA does the grunt work for you, does that mean it converts bonus and shift tolerances to independent variables?
I have not used VSA and is interested how it prefers the RSS inputs. Where I work we are expected to input bonus and shift tolerances as separate lines in our...
Sometimes when I want to move a component in an assembly the option "By Constraints"
is not available. It is grayed out. How/why does this happen?
L. Jones
NX 7.5.4.4
TC 2007.2.2.3
This is a problem where I work too. We wave link in many standard features in our products. Ever since going to NX 7.5 the only way we could get the files to update was use Edit-Feature-PLayback.
