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Stackup Tolerance Study.

Stackup Tolerance Study.

Stackup Tolerance Study.

(OP)
Hi, I am trying to find a good example of “stackup tolerance analysis.”  For example, parts bolted to each other & the total stackup not to exceed such & such using RSS method.

Thanks.
Al.

RE: Stackup Tolerance Study.

"Root Sum Squared" analysis or sometimes called "the law of propagation of uncertainty" is a method of combining uncertainty components estimated as standard deviations.
If i'm correct then its a method of combining components in a mathematical model, but i dont think tolerances can be simply combined using Root Sum Squared. The maths assume normal distribution and this might be un-conservative as it excludes the possibilites of items being at the max/min end of their tolerance boundaries. It is better suited to a large amount of items where statistically they will follow the standard deviation trend as a whole. However never having carried the process out i'm probably not the best suited to give you full guidance.

Practically speaking though, i would think that the allowable stack-up of a particular group of items would be dependant upon the relative geometric properties of each. I was always told that if it looks good then it probably is, if it looks cr*p then...

RE: Stackup Tolerance Study.

If it matters then take care of your stackup with dimensioning at the assembly/installation level.  

RE: Stackup Tolerance Study.

Well said sigma38, prevent the problem at root, rather than spending time/money trying to prove that it isnt a big problem

RE: Stackup Tolerance Study.

Sorry the previous post link didn't work. Searcg for ToleranceCalc in the turbocad web site.

RE: Stackup Tolerance Study.

(OP)
Thanks for everyone’s input.

I have recently purchased a book, “Mechanical Tolerance Stackup And Analysis” by Bryan Fischer & would take me a little bit to go thru all of it, it has lots of examples from aerospace.  Also, the last post is very informative.

We’ll talk more soon...

Al.

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