Stackup Tolerance Study. 1

[sxb060411]

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.

 

[KENAT]

Drafting Standards, GD&T & Tolerance Analysis Forum

forum1103

If you don't get the answer you need here, people thrown on double posts though.

 

[40818]

"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...

 

[sigma38]

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

 

[40818]

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

 

[dgapilot]

I haven't used this but IMSI software has this tolerance stack analy

http://www.turbocad.com/Products/PluginsandAddons/ToleranceCalc40/tabid/146/Default.aspxsis

software:

 

[dgapilot]

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

 

[aspearin1]

http://adcats.et.byu.edu/

http://WWW/Publication/87-5/WAM2.html

Aaron A. Spearin
ASQ CSSBB

http://www.Engineering6ss.com

"The only constant in life is change." -Bruce Lee

 

[sxb060411]

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.